(updated August 15, 2002)

 Course Description:

This course is a survey of the taxonomy, ecology, evolution, morphology, and physiology invertebrate phyla. In both lecture and lab, you will be examining living and preserved specimens. An integral part of the course is participation in two field trips. The first one is to the Gulf Coast Research Lab, located at Ocean Springs, MS, where we will collect and examine living specimens.

 To the Course Description for the Lecture and Lab
Specimen List

 Index of phyla 

Supplemental Information

Sarcomastigophora (Amoeba and flagellated protozoa)


 Apicomplexa (aka Sporozoa, Protists endowed with an apical complex)


 Ciliata (ciliated protists) 


Porifera (Sponges)




Introduction to Hydroskeletons






















Natural History Museum in London offers the following web site on echinoid anatomy and life history:


 Nonvertebrate Chordates


  • Internal transport
  • Respiration
  • Excretion
  • Reproduction

 Ecology & Evolution



 Special Topics:


 Miscellaneous Groovy Web Sites


 Biodiversity of:









A stroll through the phyla


Sarcomastigophora - includes amoebae and flagellates.

 Dinoflagellida - typically have two flagella, some are photosynthetic.

  • Ceratium

Euglenida - typically photosynthetic, but will ingest smaller organisms like a heterotroph. Typically freshwater. Have two flagellae.

  • Euglena

Volvocida - includes colonial species. Demonstrates sexual reproduction, as in Chlamydomonas

  • Volvox.


Kinetoplastida - Parasites in invertebrates and vertebrates, endowed with flagellum and/or undulating membrane for movement

Diplomonadida - bilaterally symmetrical, parasitic in vertebrates.

Trichomonadida - Entirely symbiotic. Includes many species living in the gut of termites. Some are parasitic.

Hypermastigida - present in the gut of wood-eating insects.

  • Trichonympha

Gymnameobia -Freshwater, movement and capturing prey mediated by pseupodia.

  • Amoeba proteus

Foraminiferida - Secrete a test, generally calcareious.

  • Elphidium -Typically marine. Feed on microorganisms such as bacteria & diatoms.

Radiolarians - strictly marine, nearly all planktonic, abundant in open ocean. Hard skeletons consist of silica or strontium sulfate. Feed on diatoms, algae, protozoans.

  • Heliosphaera

Groovy web sites:

University of California-Berkeley




Apicomplexa - undergo alternation of generations with sexual and asexual reproductive phases. Entirely parasitic in at least one phase of life cycle.

Order Coccidea - internal parasites that live in the gut epithelium and other tissues of both vertebrates and invertebrates. Can cause serious disease among humans and domesticated animals.

Order Haemosporida - requires two hosts, definitive host is invertebrate (often an insect). Blood parasites among vertebrates.

Groovy Web sites:

University of California - Berkeley


 Ciliata (Ciliophora)

Ciliophora - Cilia used for both movement and the capture of food particles. Demonstrate both asexual & sexual reproduction

Subclass Hymenostomatia - well defined buccal cavity is located in anterior third of body.

  • Paramecium

Opalinata - Considered to be ciliates. Found in rectum of frogs and toads.

  • Opalina

Groovy web sites:

University of California - Berkeley 


Review slides:

Types of cells found in Porifera

  • Choanocytes have a flagellum to entrap food.
  • Pinacocytes - Cells at base produce material that affixes sponges firmly to substratum. Generally flattened, enable limited internal movement.
  • Porocytes - Doughnut shaped cells which allow water to enter the sponge.
  • Amoebocytes - mobile cells, involved in transport of gametes & food.

Other features of Poriferans

  • Mesohyl = gelatinous matrix between cell layers. Rich in collagen. Collagen found in bath sponges is concentrated into coarse but supple fibers, called spongin. Living components in mesohyl are mostly amoebocytes.
  • Spicules - spines consisting of either calcium carbonate or silica. Originate in mesohyl.


Types of Sponges: Internal morphology is basis for designation of sponge type.

  • Asconoid - Simplest type - forms mats of whitish tubes that are 2-3 mm in diameter. Central cavity = spongocoel. Fuzzy appearance of Leucosolenia is due to spicules sticking out between the pinacocytes. Spicules consist largely of calcium.
  • Syconoid - Body wall is pushed out into hundreds of fingerlike projections. Radial canal in each projection is lined by choanocytes and leads to central cavity - has calcareous spicules.
  • Leuconoid - More elaborate than other two. Choanocytes line small chambers located between the outer surface. Most have silicious spicules. In almost any marine habitat, silicious leuconoid types predominate.


Sponge physiology - Water velocity affects movement of H20 through sponge.


Sexual reproduction & Development

  • Most are hermaphroditic. A particular specimen produces one type of gamete at any particular time.
  • Sperm-producing cells undergo normal meiosis.
  • Oocytes usually do not undergo meiosis until they have been penetrated by sperm.
  • Cleavage of fertilized egg takes place is mesohyl. Swimming larva is produced & released with exhalant current.
  • Early embryo turns "inside out" to expose flagellae.
  • Asexual reproduction & gemmule formation is accomplished by budding in which groups of cells, mostly amoebocytes differentiate into small sponges that are released from surface or through oscula. Gemmules are derived from mesohyl, found in spp. of freshwater family Spongillidae. Capable of surviving cold and desiccation.


Regeneration & Reconstitution

  • Capacity to reconstitute is so great that if a sponge is squeezed through a fine-meshed cloth, individual cells will group & form >= sponge.
  • Some may accept grafts from other individuals.



  • Calcaria - marine & mostly restricted to shallow water.
  • Demospongiae - 95% of known spp. belong here. Includes bath sponges & all freshwater sponges. Have Leuconoid structure.
  • Hexactinellida - Strictly marine. Large. "Choanocytes" lack nuclei, called collar bodies.


Fossil sponges

  • Fossils found in Cambrian period.
  • Greatest diversity during Cretaceous.
  • Choanoflagellates = precursors to choanocytes. 

 Groovy web sites:

University of California - Berkeley



Review slides:

General Features

  • Includes 10,000 living spp., and numerous species of corals are found in the fossil record.
  • Gut is a sac - gastrovascular cavity, functions as a kind of circulatory system. Feeding by ciliated cells in gastrodermis.
  • Two life forms - Polyp, attached to substrate; Medusa, free-swimming. Some species show both life forms as part of serial polymorphism.
  • Orientation - along oral -aboral axis. Show radial symmetry.
  • Tissues: Includes epidermis and gastrodermis. The mesoglea lies between the epidermis and the gastrodermis. It is composed of mucopolysaccharides and collagen. The function of the mesoglea is to provides support for movement, especially for medusa forms, e.g. Jellyfish.
  • Nematocysts are cells which shoot out a thread that engages prey or predator, by penetration, entanglement, or adhesion. These cells are secreted or produced by nematocyte. Stimulus may be chemical or tactile. The three types of nematocysts include penetrants, volvents, and glutinants.
  • Bioluminescense showed by some spp. May be for defense, communication.
  • Skeleton: May be hydrostatic, as is case with sea anemones & hydra, or may include hard skeleton, made of sclerotized protein or calcareous material.
  • Sexual Reproduction: Sexes are almost separate. Fertilization may take place while eggs are still in the ovary or in the gut. Blastula stage is absent.

Hydra as an example

  • Found only in polyp form.
  • Myofilaments in the myoepithelial cells of the epidermis are parallel to oral-aboral axis, allow for shortening & thickening of the column. Gastrodermal counterparts are at right angles to those in epidermal cells. Contraction allows for column elongating.
  • Generally reproduce by asexual budding - extension of column to the side, eventually reaches size large enough to separate.
  • Sexes usually separate with spermaries forming closer to oral opening. Sperm released from opening at the tip of each spermary. An egg becomes exposed to sperm when a portion of the epidermis that covers it ruptures.
  • Hydras have all three functional types of nematocysts.



Class Hydrozoa

  • Most show serial polymorphism.
  • 3,000 living species, includes hydra & some jellyfish. Some have external calcareous skeletons.
  • Typical example is Obelia. Marine genus, abundant in littoral zone, attached to floating docks, pilings, each branch has coenosarc & perisarc. The coenosarc includes the gastrodermis, epidermis, and mesoglea, while the perisarc is hardened protein secreted by epidermis.
  • Hydrotheca = feeding polyp, gonozooid = reproductive polyp. Obelia medusae have 16 tentacles, promenent extension to which mouth is located, & 4 radial canals. Feeds on crustaceans & other small organisms. Have 4 compact gonads, sexes are separate. The Suborder Thecata (Leptomedusae) includes Obelia, Aglaophenia, which grows in featherlike pattern. The Suborder Athecata (Anthomedusae). Perisarc is usually present, but it either stops short of the hydranths or encloses only the lower portion. Gonozooids have no perisarc at all. Examples include Tubularia and Hydractinia. Freshwater hydras included here.
  • Suborder Limnomedusae, includes Gonionemus. Each tentacle has a sticky "knee" used for attachment to eelgrass or algae. Polyp phase is minute and has ~4 tentacles.
  • Order Siphonophora - includes Physalia, Portuguese man-of-war. Pneumatophore may be >15 cm, floats above water surface. Gastrozooids lack tentacles, also includes dactylozooids (batteries of nematocysts) & gonophores. Tentacles of dactylozooids may be several meters in length. Prey = fish.

Class Scyphozoa

  • Jellyfishes which lack a true velum and whose gonads originate from the gastrodermis.
  • Aurelia as an example of the Scyphozoa. Medusae = 10 to 20 cm in diamter. Most of animal consists of firm mesoglea, uses ciliary method of feeding. Sexes are separate. Sperm discharged into sea. Eggs fertilized in stomach and undergo early development in pockets on the oral lobes. Within 2-3 days, embryo becomes a type of polyp called a scyphostoma. Develops 16 tentacles. May undergo asexual budding to form additional scyphostoma, but eventually it divides eventually it divides transversely into a number of prospective medusae. Young medusae are called ephyrae.

Class Anthozoa

  • No medusa stage in life history. Gonads derive from gastrodermis. Fertilized eggs develop into planulae, which become new polyps. Sexes are separate.
  • Metridium is included in the Order Actinaria.
  • Symbiotic associations w/crabs or snail shells occupied by hermit crabs, may provide protection from predators of hosts, which give organisms a free ride.
  • Order Scleractinia: Cup corals & Stony corals. Colonial scleractinians predominate in coral reefs. New polyps produced by budding. Living tissue restricted to surface portion. All reef-building have zooxanthellae in their gastrodermal cells, differ in degree of dependence.
  • Coral reefs have high productivity, comparable to terrestrial farmland, 20 g/m2/day, as opposed to 0.2 g/m2/day in open seas.

 Three types of coral reefs:

  • Fringing - extend as platforms from edges of volcanic islands.
  • Barrier reef - Follow shoreline but separated by lagoon.
  • Atoll - reef that encircles a lagoon.

 Gorgonians - includes sea whips & sea fans. Stiffened by protein-collagen mixture and/or calcareous spicules.

Groovy web sites:


Review slides:  

General characteristics

  • Includes about 100 spp., all of which are marine and are predators.
  • Superficial similarity to medusa forms of Cnidaria, with an outer epidermis, inner gastrodermis, and thick, gelatinous middle mesoglea layer.
  • Ctenophora have radial symmetry, with oral and aboral surfaces. (See )
  • Incomplete digestive system, in which main gastrovascular canal diverges into 4 canals, two of which are "blind alleys" and two are connected to apical anal pore.
  • Locomotion, which is mouth forwards, is via comb rows of partially fused cilia. These comb rows account for Greek name.
  • Tentacles are "armed" with colloblasts. They have a bulbous, sticky head connected to a long filament. Tentacles are retracted to bring food to the mouth. Tentacles can be 100x length of body.
  • Prey include small crustaceans, larval stages of fish & shellfish.
  • Nearly all species are bioluminescent.


  • Simultaneous hermaphroditism is characteristic of this phylum.
  • Embryo usually looks like miniature adult (= cydippid larva)
  • Details of embryonic development differ significantly from Cnidaria.
  • Some species can undergo asexual reproduction through fragmentation.

Groovy web sites:



Review slides:

General Characteristics

  • 11,000 spp., about 3/4 are parasitic
  • These organisms are organized at the organ level, with discrete reproductive & digestive organs. They are all acoelomate, in which the body cavity is filled with parenchyma. Most are hermaphroditic, and it is the first phylum showing evidence of cephalization.


  • Class Turbellaria - Mostly free-living, ventrally flattened. Ventral surface is ciliated. Complete digestive system.
  • Class Digenia - Entirely parasitic, require >= 2 hosts. Complete digestive system. First intermediate host MUST be a mollusc, usually a snail. One miracidium penetrates snail, changes morphology to a sporocyst. Sporocyst undergoes polyembryony, a type of budding, to generate numerous sporocysts. Polyembrony occurs in sporocysts to produce redia. Polyembryony also occurs in redia to produce cercariae, which are the larval form which emerges from the snail. Cercariae may be infective to definitive host or they may encyst on a second intermediate host, forming a metacercarial stage.

Clonorchis sinensis life cycle: Adults reside in bile duct. Produce eggs which are eliminated with feces. Ciliated larva (miracidium) hatches, & is ingested by appropriate sp. of snail. Larva loses cilia, becomes a sporocyst. Sporocyst undergoes polyembryony to generate redia. Redia reproduces asexually to produce cercariae which emerge from snail. Cercariae penetrate cyprinid fish (especially carp) to form metacercariae. People become infected by eating inadequately cooked fish.

  • Class Monogenea - require only one host for entire life cycle. Many are parasites of fish -- gills and skin. Organisms are equipped with hooks and suckers for adhering to skin.
  • Class Aspidogastrea - may be ancestral worms, from which Digenia evolved. Aspidogaster conchicola is found in pericardial cavity of freshwater unionid clams. Eggs reach the mantle cavity by way of renal organs & are swept out with the exhalant water current. How worms penetrate pericardial cavity is unknown.
  • Class Cestoda: Entirely parasitic. Adults live in the intestine and bile ducts of vertebrates. They have no digestive system. All nutrients are absorbed directly through the tegument. Lengthening of animal from scolex (holdfast organ) is by strobilization = development of segments, each of which has complete male and female reproductive systems. As segments are moved further away, they mature, and male rep. system deteriorates to provide protein for developing eggs. Gravid (egg-laden) segments either fall off intact or get sheared off.

Echinococcus granulosus: useful as demonstration organism because it consists only of a scolex, one immature segment, one mature, and one gravid segment at any one time. Adults live in intestines of dogs. Eggs laid in feces. Sheep, pigs & ungulates ingest eggs with food, larva develops in musculature. Dogs acquire infection by eating meat. The larval stage causes severe disease in humans.

Groovy web sites:

 Introduction to Hydroskeleton

  Functional definition of a skeleton

  • A solid or fluid system permitting muscles to be stretched back to their original length following a contraction. Such a system may or may not have protective and supportive functions as well.
  • Other types include endoskeleton and exoskeleton

Requirements for a hydroskeleton

  • The presence of a cavity housing an incompressible fluid that transmits pressure changes uniformly in all directions;
  • That this cavity be surrounded by a flexible outer body membrane, permitting deformations of the outer body wall to take place;
  • That the volume of fluid in the cavity remain constant;
  • That the animal be capable of forming temporary attachments to the substrate, if progressive locomotion is to occur on or within a substrate;
  • Generally, these types of animals have at least 2 pairs of musculature oriented in different directions, i.e. longitudinal and circular muscles.

Phyla whose species have hydroskeletons:

  • Nematoda (have longitudinal fibers only)
  • Acanthocephala
  • Annelida

Groovy web sites:






  • Most are marine
  • One genus is freshwater, and several species across several genera are terrestrial

Nemertines superficially resemble free-living Turbellaria (Phylum Platyhelminthes)

  • Are ciliated externally and secrete mucus.
  • Flattened dorsoventrally and posess circular, longitudinal and dorsoventral muscles.
  • Nervous system resembles that of turbellarians.

Nemertines differ from flatworms in a number of ways

  • Nemertines possess a circulatory system. Their circulatory system lacks a heart, and blood vessels lack one-way valves.
  • Nemertines also possess a complete digestive system.
  • Nemertines also possess a proboscis which can be everted explosively. In most species, the proboscis is used to trap prey. Some species also have a stylet, with which they stab their prey and inject a paralytic toxin.
  • Most species species are dioecious, although a few are protandric, in which younger individuals are male, and then become female as they get older.
  • Most have larval stages that resemble a juvenile worm, but the order Heteronemertea develop into pilidium larvae. These are "long-lived, ciliated, swimming feeding individuals resembling football helmets with earflaps. Juvenile worm develops from fusion of imaginal discs.

Groovy web sites:

University of California - Berkeley



  Defining Characteristics:

  • Highly muscular pharynx containing jaws (trophi) for grasping, crushing, or grinding prey;
  • Toes with adhesive glands.
  • Possess a ciliated surface called the corona. Cilia on the corona beat metachronally, thus giving the illusion of rotation.


  • Most of the 2,000 species live in freshwater
  • 5% are found in shallow-water marine environments, and a few of them a parasitic in invertebrates.

Digestive system

  • Is complete among Rotifers
  • Possess a prominent, muscular modification of the pharynx called a mastax. Within the mastax, there will be rigid structures called trophi, which are used to grind food following ingestion.


  • Free-living rotifers use coronal cilia, others use spines.
  • Still others, such as Philodina roseola will use looping locomotion to move across substrate.
  • Some are sessile as adults, planktonic as juveniles.


  • Class Seisonidea are dioecious, while Bdelloidea and Monogononta are parthenogenetic.
  • Most individuals which are collected at any time of the year will be female.

Groovy web sites:

University of California - Berkeley



Review slides:  

General characteristics

  • Parasites found in the gut of vertebrates
  • Body shape is cylindrical, small
  • Large pseudocoel which serves as gonads & uterus in females.
  • Sexes are separate
  • Lack specialized excretory system.
  • Unlike nematodes, they have circular muscles
  • They lack a digestive system, so nutrient acquisition is via the tegument.

The name for this phylum is derived its retractable proboscis

  • Proboscis has hardened hooks and spines.
  • Morphology used in species identification.
  • The spines are used to maintain position in small intestine of its definitive host.

 Acanthocephalans require an arthropod intermediate host and sometimes a "transport" host.

  • Larvae inside eggs develop into acanthor stage within pseudocoel of female. The larvae are passed in the feces of the definitive host, and are ingested by or penetrate 1st intermediate host, an arthropod. The arthropod is usually an insect in terrestrial habitats, and a crustacean in aquatic habitats
  • Larvae develop to infective acanthella stage.
  • Infective acanthella stage often modify host behavior to facilitate capture of intermediate host by definitive host. An example of this is the modification of gammarid behavior by Polymorphus paradoxus. The behavior of the intermediate host (Gammarus sp.) to make it more conspicuous to the definitive hosts, which are predators of gammarids. *From Holmes, John C.; Bethel, William M. 1972. Modification of Intermediate Host Behaviour by Parasites. Behavioural Aspects of Parasite Transmission, E. U. Canning & C.A. Wright, editors. Supplement No. 1 to the Zoological Journal of the Linnean Society, Vol. 51:123-149. (See Figure 1.)
  • 1st intermediate host may be ingested by transport host, which facilitates passage to definitive host, but in which there is no physiological development.


 Groovy web sites:

Ohio State University


General Characteristics

  • General characteristics: Bilateral symmetry, lack of segmentation. Body organized into four main regions: head, foot, visceral mass, mantle.
  • The head has the mouth & accessory structures. Most notable is the radula, a ribbon with cutting teeth. As teeth wear off, they are replaced.
  • The foot is muscular and used for crawling, burrowing, clinging.
  • The visceral mass contains a proportionately large part of the body. The gut & digestive gland, latter consisting of diverticular of the stomach. Intestine, at least in gastropods, is small. Visceral mass also contains the excretory organs, heart, pericardial cavity, gonads, and other components of the reproductive systems. The derivatives of the embryonic coelom are the pericardial cavity (which surrounds the heart), the renal organs, and gonads and gonoducts.
  • Mantle, composed of soft tissue, covers the visceral mass. Its epidermis, which secretes the shell (when present), is continuous with that of the foot and head region.
  • Sexes are separate.
  • Torsion characteristic of gastropods. During development, a combination of muscle contraction and differential growth brings the posterior portion of the mantle cavity cavity forward, above the head. Hence, the epithet of "shithead" is perfectly appropriate for gastropods.
  • Gastropods includes snails, slugs, nudibranchs, and opisthobranchs.
  • Bivalves include clams and muscles. They have a two-piece shell. Valves hinged together dorsally. Ctenidia have enlarged ctenidia which serve as gathering organs for food particles. Food gets caught on mucous layer covering ctenidia, food is swept forward to mouth.
  • Cephalopods include squids and octopuses. Adapted to capture small prey and for rapid swimming. Unlike the open circulatory systems of the other molluscs, these organisms have closed vessels for transporting blood.

Class Gastropoda

  • Constitutes the largest molluscan class, with marine, freshwater & terrestrial representatives, and includes snails and slugs.
  • Snail consists of visceral mass on top of a muscular foot. The visceral mass is protected by a shell, which is typically coiled, leans left, but coiled dextral.
  • A separate process is torsion, anticlockwise, a twisting of the body. Twisting through 180o occurs during early development. Nervous & digestive system become twisted, while the mantle cavity moves from rear to above head. Asymmetry is due to asymmetric development of retractor muscle. Retractor muscles attach head foot of embryo to shell. Torsion can take as little as a few hours or minutes.
  • Adaptive significance of torsion is obscure. Advanced species show reduction of degree of torsion, while some spp. show detorsion.
  • Movement by pedal waves of muscle contraction
  • Subclass Prosobranchia. This is the largest of 3 gastropod subclasses, mostly marine. They are generally free-living & mobile, and include herbivores, omnivores, carnivores and deposit feeders. They are considered the most primitive of gastropods. They have a rigid disc called operculum, closes animal in shell for protection. Gill cilia move H2O into mantle cavity across gill sheets. A portion of mantle may be extended into siphon.
  • Subclass Opisthobranchia. This subclass includes sea hares, sea slugs, & bubble shells. Approximately 1,100 spp. Described. They are characterized by reduction or loss of shell, operculum, mantle cavity, ctenidia. The function of gas exchange is taken over by mantle extensions called cerata. Some opisthobranchians use unfired cnidarian nematocysts for defense.
  • Subclass Pulmonata. This includes approximately 20,000 species, most of which are freshwater or terrestrial. It includes slugs, snails & escargots. The shell may be reduced, internalized, or lost. The mantle cavity is highly vascularized to function as lung. Flow of air/water is through pneumostome.

Class Bivalvia: Includes 25K contemporary spp. of clams, scallops, & oysters.

Major characteristics include

  • Hinged shell, with 2 valves joined by springy ligament
  • Lateral compression of body & foot
  • Virtual absence of head & assorted sensory structures.
  • Spacious mantle cavity
  • Absence of radula-odontophore complex
  • Shell opens ventrally
  • Foot projects ventrally & anteriorly
  • Siphons, when present, project posteriorly.


  • Most are marine, few freshwater, no terrestrial. The Class includes includes two subclasses
  • Subclass Protobranchia are considered more primitive & are entirely marine. Gill filaments divide mantle into two chambers, incurrent (ventral) & excurrent (dorsal). Most food collection is by palp proboscides, which are long thin muscular extensions of tissues. The extensions surround mouth and food is trapped by surface mucus brought to labial palps
  • Subclass Lamellibranchia includes most bivalves. All freshwater bivalves are included here in the Unionidae. Water enters incurrent siphon, and passes dorsally between gill filaments. Water then exits via more dorsally-located excurrent siphon. Gills, which are thin and greatly elongated are involved in both gas exchange & nutrient acquisition. Some lamellibranchs have symbiotic bacteria, which undergo chemosynthesis, in which energy is derived from sulfides, HS-, or methane. The presence of these symbiotic bacteria is associated with reduction of bivalve digestive system. Some bivalves live on hard substrates, anchored by byssal threads, which are proteinaceous secretions. Most bivalves burrow into soft substrate.

 Class Cephalopoda 

  • Fast-moving active carnivores, all marine.
  • Entire body of nautilus is found in outermost chamber of shell.
  • Nautilus is a type of cephalopod, with a shell divided by septa. The septa are penetrated by a siphuncle which has blood supply. The siphuncle also regulates gas content, hence buoyancy. Animal moves by jet propulsion, expelling water -- water emerges from siphon or funnel.
  • Other cephalopods lack an external shell. Among these, the mantle then plays a major role in movement. In squid, shell is internal, reduced in size, called a pen. In octopus, shell is absent.
  • Loss of shell associated with alternative defense strategies. Chromatophores cause change of color, thus allowing camouflage. Some cephalopods also secrete ink from an ink gland.
  • Cephalopods have a closed circulatory system. The oxygen-carrying protein is hemocyanin, which is found in the liquid fraction of blood, not in cells.
  • Have a large, highly differentiated brain.
  • Cephalopods do not show responses to sound stimuli.
  • Squid and octopi have VERY advanced visual systems, representing an example of convergent evolution with vertebrate eye. They can perceive shape, color intensity & texture. The eyes are image-forming, similar to vertebrates Eyes have structures analogous to those of a vertebrate eye -- Cornea, lens, iris, diaphragm, retina. Unlike vertebrates, focusing is by moving lens relative to retina, unlike vertebrates.

Miscellaneous Classes

 Class Polyplacophora, common name: chitons.

  • All are marine, close to shore, in the intertidal zone, ~800 species.
  • Shell has 8 overlapping & articulating plates on dorsal side.
  • Nervous system is reduced
  • Feeds on algae scraped off rocks.

 Class Scaphopoda, common name: Tusk shells

  • Considered an evolutionary young group, "a mere 450 million years old."
  • 300-400 spp., live on sand or mud substrates, deep water.
  • Shell is linear, holly curved tube, hence common name.
  • Shell has openings at each end, water enters at narrow end.
  • Ciliary action causes water movement.
  • Several organ systems are lacking, including ctenidia (for gas exchange), and a heart & circulatory system. The foot's rhythmic movement circulates blood. Blood moves through hemocoel.
  • Burrows into substrates for food, uses captacula to snare food.

Class Monoplacophora

  • Known only in fossil record prior to 1952.
  • ~12 spp. named, all from deep marine water.
  • Single unhinged shell.
  • Mantle cavity takes form of 2 lateral grooves
  • 5-6 pairs of gills hand down within mantle groove
  • Important group, since they may be ancestors to others.

 Class Aplacophora

  • Worm-shaped, found in deep marine water.
  • Most are small, several mm in length, rarely > few centimeters
  • Body is unsegmented, no true shell.
  • No conspicuous foot.
  • <300 spp. many based on 1 or 2 spp.

 Groovy web sites:

University of California - Berkeley

Information about Cephalopods



Introduction & General characteristics

  • All 12 described species are marine.
  • Densities can reach several thousands/m2.
  • Some live in shallow waters, 20-25 m depth.
  • Most live in depths of hundreds to thousands of meters.
  • Most of pogonophoran body does not indicate close evolutionary relationship with annelids.
  • Anterior region bears a cephalic lobe. There is also a "beard", consisting of one to thousands of ciliated tentacles, and a glandular area which secretes a chitinous tube, within which animal spends its life. The tubes are always longer than worms residing in them. Each tentacle is served by 2 blood vessels, hence tentacles are primary gas exchange surface. The longest part of body is the trunk, which contains a pair of uninterrupted coelomic cavities. The body wall has both circular and longitudinal muscles. The trunk is unsegmented, and is often marked by papillae (small bumps). The body cavity is not septate
  • Major organs include gonads and trophosome. The trophosome is tightly packed with bacteria. The posterior body region is the opisthoma which has conspicuous (~6-25) segments, each containing a coelomic cavity. Each segment of opisthoma bears annelid-like setae.
  • 18S ribosomal RNA shows affinity between annelids & pogonophorans
  • No digestive system observed in adults, although some larval forms have complete digestive systems. Experimental evidence suggests that pogonophorans depend on DOM (Dissolved Organic Matter) from sea water. Active uptake drawn from very dilute seawater. Concentrations of DOM in water can be as low as 1 x 10-6 moles/liter.
  • J. Most pogonophorans, e.g. Perviata, are 6 cm to 36 cm long, ~1 mm wide.

Vestimentiferans are an unusual group.

  • Some can be up to 2 m in length, 25 mm to 40 mm wide.
  • Found at or near hydrothermal vent, where water temperature can range from 2oC to near boiling, & is rich in hypersaline sulfide & methane. The trophosomes have numerous bacteria which can oxidize H2S or methane. Sulfides and methane diffuse into the blood.
  • CO2 + H2S + O2 ® [CH2O] + H2SO4
  • Host either ingests bacteria or liberated soluble carbohydrates.
  • Such chemosynthetic bacteria are also found in several mollusc and at least one polychaete animal.
  • Vent & seep pogonophorans differ from others, by possession of a long collar called a vestimentum, just posterior to the plume of tentacles and a large anterior structure called the obturaculum.

Other Aspects of Pogonophoran Biology

  • Reproduction & Development: Species are dioecious. Offspring develop for a time within parenteral tube. Early vestimentiferan larvae have complete digestive tracts. Larvae appear to be trochophore type.
  • Circulation: The Circulatory system is well-developed with a distinct heart anteriorly. Tentacles serve as gas exchange surfaces. Blood circulates through trophosome, supplying bacteria with sulfides, methane, and with oxygen. Blood & coelomic fluid contain 2 extracellular hemoglobins.



 General characteristics

  • Segment worms, where the segments are divided by sheets of mesodermally derived tissue (septa) Mesodermally derived tissue is called peritoneum.
  • Excretion is through body surface and via nephridia.
  • Most have a closed circulatory system. The dorsal vessel carries blood anteriorly, while the ventral vessel carries blood posteriorly. There is no specialized heart. Instead, the blood vessels themselves contract. The blood circulatory system is reduced or absent in the Hirudinea.
  • Most species have oxygen-carrying blood pigments. The most frequently-encountered blood pigment is hemoglobin. Chlorocruorin, an iron-containing molecule, and Hemerythin is also found.

Class Polychaeta

  • Includes 70% of all annelid species, most of which are marine.
  • Sensory organs include eyes and at least one pair of sensory appendages.
  • In some species, the body wall extends into thin outgrowths called parapodia. These parapodia function in gas exchange, and may function in locomotion. Setae may be present on parapodia. Parapodia may be reduced or absent in sedentary species.
  • Sedentary species have threadlike or feathery outgrowths & anterior end for gas exchange and/or food capture, e.g. Nereis.
  • Epitoke formation preceeds sexual reproduction. Epitokes = sexually mature being that is highly specialized for swimming and sexual reproduction, and fertilization is internal.
  • Polychaetes form a trochophore larva, which is free living, and has a digestive system with 2 rings. The larva adds segments as it gets older.
  • Some species can reproduce asexually by fragmentation and regeneration of missing body parts.

Class Oligochaeta

  • Includes 3,000 species, most of which live in freshwater or terrestrial habitats.
  • Parapodia are lacking, and the anterior part of the body lacks conspicuous sensory structures, such as eyes.
  • Setae are present, but are scattered.
  • Respiration is across most of the body wall.
  • Species are simultaneous hermaphrodites, in which there is simultaneous exchange of sperm by both individuals. Miniature worms emerge from the cocoons -- there is no larval stage. In Lumbrucus terrestris, the clitellum is the region where the cocoon develops for embryo development.

Class Hirudinea

  • Includes 500 described species, found mostly in freshwater and marine habitats.
  • Parapodia and head appendages are absent.
  • Species are simultaneous hermaphrodites, and fertilization is internal.
  • Species are endowed with a clitellum.
  • Gill structures are absent.
  • Most lack setae.
  • There is no compartmentalization with septa. Instead, the continuous coelomic space is largely filled with connective tissue, i.e. mesenchyme. Channels and sinuses within tissue, and coelomic fluid serve a blood transport function.
  • Anterior and posterior sucks are present.
  • Most are ectoparasitic, feeding on blood, mostly on vertebrates.


The exoskeleton is a characteristic feature of this phylum

  • Secreted by epidermal cells.
  • Outermost layer is a waxy epicuticle, which is composed of lipoprotein underlain by layers of lipid. The cuticle is water-impermeable and gas impermeable.
  • Bulk of exoskeleton is chitin, a polysaccharide associated with proteins, and it is strong, non-allergenic and biodegradable.
  • The presence of an exoskeleton necessitates periodic molting. The new cuticle forms underneath the old one. The old cuticle is enzymatically degraded & split, and the animal "crawls" out of old cuticle.
  • Ecdysis and formation of new exoskeleton under neural & hormonal control.

Neural control of muscles is different than in mammals.

  • Strength of contractions proportional to pulse frequency
  • Muscle fibers can be innervated by up to 5 neurons.
  • Musculature is entirely striated. As a result, muscles are more responsive, and the reaction time reduced. This allows for coordination of flight.

Circulatory system is open.

  • Blood leaves heart by arteries
  • Blood enters heart via ostia.


Arthropods constitute the largest phylum in Animal Kingdom

Subphylum Trilobytomorpha has one class, the Trilobita

  • No living representatives, 4K spp. in fossil record.
  • They were common 500 Million years ago, and were extinct by 250 million years ago
  • Trilobytes showed a varied life style, including burrowing, walking, and swimming

Subphylum Chelicerata lack antennae

  • Class Merostomata These animals are mostly extinct, represented by only 4 living spp., including the horseshoe crab. They are entirely marine, with a limited distribution.
  • Class Arachnida. Early forms were marine, but most of the 70K living spp. are terrestrial, and they include spiders, mites, and ticks. The head & thorax are fused into a prosoma which may have 0 - 4 prs. of eyes. The anteriormost pair of appendages on prosoma are chelicerae, whose function is to tear apart food. The next pair of appendages = pedipals, which have multiple functions, including grabbing, killing, and reproducing. The abdomen and prosoma are generally distinct. Respiration of more primitive types is with book lungs, with openings at surface called spiracles. Small spp. have trachea

Characteristics of spiders:

  • have 4 or less prs. of spinnerets
  • Abdominal appendages
  • Produce silk protein

Mites and ticks belong to Order Acari

  • Niches of mites & ticks are varied. They include omnivores, carnivores, herbivores, fungivores, and parasites
  • Feed exclusively on fluids
  • Can live in freshwater, marine, terrestrial, sand
  • Numerous organisms serve as hosts for parasitic forms
  • Class Pycnogonidae: This group, the "sea spiders", have long legs, and includes 1 K spp. They lack specialized respiratory & excretory systems, but they have complete digestive systems

Subphlum Uniramia

Class Chilopoda (Centipedes)

  • Fast moving carnivores
  • Live in moist soil, humus, under logs.
  • Most are terrestrial, cuticle is unwaxed.
  • Chilopods have a single pair of antennae, a pair of first & second maxillae, and a pair of maxillipeds, which are modified to subdue prey
  • Lack eyes, but oceli, or eyespots may be present
  • Chilopod head followed by 15 or more leg-bearing segments

Class Diplopoda (Millipedes)

  • 10 K spp.
  • Slow moving, plow through soil & decaying organic matter
  • A few carnivores
  • Pairs of segments have become fused, each new segment has 2 pairs of legs and 2 pairs of spiracles.
  • Covering is impregnated with calcium salts, which makes more protected. This covering is not waxy
  • Ocelli are present

Class Insecta

  • Found in all habitats except deep sea
  • Nearly 1 million spp. Named, 3x that to be named.
  • Success due to several factors, including feeding specializations, dispersal capabilities, predator-avoidance possibilities, and flight

Insect visual systems

  • Ocelli are small cup with light-sensitive surface. The surface is backed by light-absorbing pigment. This type of visual system is found in many phyla, including Platyhelminthes, Annelida, Mollusca, and Arthropoda. They are often covered by a lens, and each insect head usually has 3 ocelli. Ocelli are NOT image forming.
  • Compound eyes are image forming. The individual units are called ommatidia, and each one has a non-focussing lens. They have fewer receptor cells than in mammal eye. The image that is produced by the ommatidia has a very wide angle visual field, and is coarse-grained image is produced.
  • Components of ommatidium include a fixed lens with a high depth of focus, a crystalline cone, retinular cells, shielding pigment, and a neural cartridge.
  • Insect eyes are sensitive to polarized light, which can be used for navigation. Some are sensitive to UV & Infrared light

Other insect characteristics

  • Head bears 4 prs. of appendages, including one pair of uniramous antennae, 3 pairs. of mouthparts (mandibles, maxillae, and mandibles.)
  • Gas Exchange by tracheal system. Spiracles are paired on segments, spiracles can be closed to prevent H2O loss.

Uric acid is primary nitrogenous waste.

  • It is excreted in nearly dry, solid form.
  • Formed by Malpighian tubules
  • Up to 250 prs. of tubules in hemocoel.

Insect flight

  • Wings are thin, lightweight, outfoldings of body wall.

Subphylum Crustacea

Class Malacostraca contains 75% of all described spp.

  • Includes decapods, euphausiids, stomatopods, isopods
  • Typical head is tripartite: head, thorax, abdomen. The head & thorax typically fused & covered by carapace
  • Appendages are biramous, i.e. 2 branches.
  • Many spp. Have chromatophores, leaving to a variety of colors. More than 1 pigment can be in 1 chromatophore Since pigment dispersion is due to hormonal control, color change is slow.

Order Decapoda is the largest & best known

  • Includes 10 K spp.
  • Lobsters, crayfish, hermit crabs, true crabs, shrimp

Order Euphausiacea is commercially important

  • Includes krill
  • < 12 spp. Described
  • Comprise major food source for marine animals
  • Generally appear like decapods, but the difference difference is in # of thoracic legs. Euphausiids have 8 prs. of legs, and the thoracic appendages have gills.
  • Krill are bioluminescent. The light -producing organs are photophores, and photophore distribution is species-specific

Order Stomatopoda are rather large (up to 35 cm)

  • Bottom-dwelling carnivores
  • Abdominal segments have gills
  • Common name is mantis shrimp
  • Most are tropical, some in temperate zone
  • Typically life in burrows in shallow water.

Order Isopoda has 10 K spp.

  • Most are marine, some freshwater, terrestrial.
  • Some marine forms are parasitic
  • Isopods lack a carapace
  • Have only 1 pair of maxillipeds
  • Small, 0.5 - 3 cm in length
  • Compound eyes are NOT stalked
  • Respiration is by flattened pleopods
  • Terrestrial forms have trachea
  • Amphipods are flattened laterally. There is no carapace, and they have a single pair of maxillipeds. There are 5,000 species, mostly marine, although some freshwater & terrestrial forms exist. Gills are found on thorax

Class Branchiopoda

  • Predominantly small freshwater group
  • Coxae involved in locomotion & gas exchange
  • Includes largest # of shrimp, e.g. fairy shrimp, for which an example is Brine shrimp, Artemia salina
  • About 800 spp. are in order Cladocera, water fleas, which dominate zooplankton of freshwater lakes

Class Copepoda has 7.5 K spp.

  • Most are marine, some freshwater & parasitic forms
  • Free-living types feed on phytoplankton
  • Usually 1-2 mm long
  • Major food source for animals
  • Most have a single, median eye on the head, in which the eye has 3 ocelli
  • Lack gills & abdominal appendages

Class Cirrepedia include barnacles, about 1 K spp.

  • Exclusively marine. Most adults free-living, residing on solid surfaces, but some are parasitic.
  • They represent a radical departure from typical crustacean body plan. Although the larvae are planktonic, the adults are sedentary and sometimes stalked. The head is greatly reduced, with the first antennae reduced, and the 2nd antennae absent.
  • The shell consists of plates -- Carna, rostrum, scuta & terga. Certain of scuta & terga are movable. Feeding appendages are called cirri, which are modified thoracic appendages, which are used to filter food from water. There are neither gills nor abdominal segments.
  • Circulatory system is open, and blood circulates by movements of body

Other Features of Arthropod Biology

  • Most are dioecious w/internal fertilization
  • Some branchiopods and insects are parthenogenetic
  • Marine spp. Often have a free-living larval stage. The nauplius larvae of several groups, such as Copepoda, Branchiopoda, and Cirripedes, look similar.
  • Nauplius morphology include triangular shape with a prominent carapace and single median eye of 3 ocelli. As the nauplius molts, the larva becomes larger, and appendages are added. In copepods, nauplius molts into copepodite stage, which appears similar to adult. In barnacles, nauplius molts into cypris stage, which is mobile and planktonic, following ocean currents. When a barnacle cypris finds a suitable substrate, it will undergo a series of changes. First, glue is secreted from anterior cement glands. Then, the head becomes attached to the substrate, and internal reorganization occurs.
  • Decapod crabs & crayfish brood their embryos externally, and advanced stages develop beneath abdomen. Zoeae larvae are released, which subsequently molt into megalopa. Megalopa look like crab, but abdomen is not tucked.
  • Isopods and Amphipods lack larval stages. Instead, the young emerge as miniature adults. The lack of free-living larval stage may be adaptation to land.
  • Internal fertilization is rule among terrestrial arthropods.
  • Females require high protein diet for egg formation. Among parasitoids, e.g. mosquitos, the protein can come from blood meals. In the case of wasps, females may oviposit in larva of another insect, and the larvae eat internal tissue of host.
  • Larvae of spp. which undergo complete metamorphosis are instars
  • Gradual metamorphosis, in which the young resemble the adult, is called hemimetabolous. This is characteristic of dragonflies, grasshoppers, cockroaches. The nymphs may have similar feeding habits to the adults. The gonads don't mature until final molt.
  • Abrupt metamorphosis, in which the immature forms do not resemble the adults, is called holometabolous. This is characteristic of flies, butterflies, wasps & bees. In the larvae of these organisms, imaginal disks are formed which will produce adult organs, and these disks remain quiescent until appropriate time in embryo.
  • Molting and metamorphosis controlled by environment & hormones. Neurosecretory cells in the brain secrete PTTH. PTTH stimates a pair of glands, called prothoracic glands in anterior thorax. The prothoracic glands, in turn, secrete ecdysone, which stimulates. The old cuticle resorbed, the and the new cuticle formed. Juvenile hormone (JH) is produced by corpora allata. High quantities of JH in blood inhibits the molting process.
  • Some insects enter resting state (diapause), which allows survival of insect during harsh conditions. Diapause may be broken by day length and/or temperature.
  • Arthropod gut is divisible into 3 areas -- foregut, midgut, hindgut. All free-living spp. Have a distinct mouth & anus, although it may not be functional system.
  • Excretory organs and nitrogenous wastes differ between aquatic & terrestrial forms. Merostomata have 4 prs. of coxal glands. Arachnida also have coxal glands, while some have Malpighian tubules. The major excretory gland of insects is Malpighian tubules. Some wastes incorporated in cuticle to be shed. Most nitrogenous waste excreted as uric acid. In Crustacea, nitrogenous wastes, mostly ammonia, are excreted through gills via simple diffusion.
  • In Crustacea excretory organs may have other functions, such as resorption of salts, elimination of water. Some have green glands which perform above functions

Major Groups

Subphylum Chelicerata

Class Merostomata

Class Arachnida

  • Order Scorpiones - true scorpions
  • Order Araneae - spiders
  • Order Opiliones - harvestmen or "Daddy Long-legs"
  • Order Acari - mites & ticks

Subphylum Uniramia

Class Chilopoda - centipedes

Class Diplopoda - millipedes

Class Insecta has numerous orders

  • Thysanura - silverfish & bristletails
  • Collembola - spring tails
  • Ephemeroptera - mayflies
  • Odonata - damselfies & dragonflies
  • Blattaria - cockroaches
  • Mantodea - mantids
  • Isoptera - Termites
  • Orthoptera - crickets, katydids, grasshoppers
  • Phasmida - walking sticks
  • Dermaptera - Earwigs
  • Plecoptera - Stoneflies
  • Psocoptera - book lice & bark lice
  • Anoplura - sucking & pubic lice
  • Mallophaga - chewing & biting lice
  • Thysanoptera - thrips
  • Hemiptera - true bugs
  • Homoptera - cicadas, aphids, mealy bugs, leaf hoppers
  • Coleoptera - beetles
  • Siphonoptera - fleas
  • Diptera - True flies
  • Trichoptera - Caddisflies
  • Lepidoptera - moths & butterflies

Subphylum Crustacea

Class Cephalocarida

Class Malacostraca

  • Order Isopoda - woodlice, pillbugs
  • Order Amphipoda - amphipods
  • Order Euphausiacea - krill
  • Order Decapoda has numerous economically imp. spp.

Class Branchiopoda

  • Order Cladocera - water fleas, e.g. Daphnia, Bosmina

Class Ostracoda - seed shrimp

Class Copepoda

  • Order Calanoida - some are freshwater only

Class Branchiura - Argulus, fish louse.

Class Cirripedia - barnacles, most free-living, few parasitic.

 Class Insecta


  • Reported from nearly every habitat except the deep sea.
  • Most are terrestrial, but some are adults or larvae in freshwater or saltwater marshes.
  • A few species are ocean striders

Nearly a million species described

  • Success of species attributable to feeding specializations, dispersal capabilities, and preedator-avoidance possibilities associated with evolution of flight.

Insects diversified before the evolution of angiosperms - surprisingly, not synchronized.

  • Study of mutual interdependence of insects & evolution of those interactions is a burgeoning field.

Insects are also widely studied because they are significant vectors of disease & major agricultural pests.

Body divided into 3 conspicuous tagmata

  • Head/thorax/abdomen
  • 2 pairs of wings are generally carried dorsally on the thorax.
  • Wings are outfoldings of thoracic integument & consists of 2 thin chitinous sheets.
  • Thorax generally bears 3 pairs of legs, oriented ventrally.
  • Legs may be modified for walking, jumping, swimming, digging, grasping.
  • Legs are generally studded with sensory receptors, e.g. taste, smell, touch.

Insect visual systems

  • Ocelli are small cups with a light sensitive surface backed by light-absorbing pigment. Such photoreceptors are found in other phyla. Photosensitive pigment of the ocellus is a vitamin A derivative in combination with a protein. Typically, there are 3 ocelli on an insect head.
  • Compound eyes are capable of forming an image. The component eye consists of many lenses, fewer receptor cells. Individual units are called ommatidia, each of which is very wide-angle. One ommatidium samples only a small part of the complete energy. Each lens has very great depth-of-focus, several mm to several meters, is sensitive to polarized light & to UV, and produces coarse-grained image.

Other Insect Characteristics

  • Insect head bears 4 pairs of appendages.
  • One pair of antennae, which are always uniramous, or single branched.
  • 3 pairs of mouthparts, including a mandible, Maxillae, and a pair of second maxillae that have fused to form a labium.
  • Mandibles are shielded anteriorly by a downward extension of the head called the labrum.
  • Gas exchange surfaces have been internalized into a tracheal system. One pair of spiracles opening into the trachea system is found in thorax, with additional pairs of spiracles located on many of the abdominal segments. Spiracles can be closed, deterring evaporative loss. The trachea is lined with cuticle, which is shed and resecreted by underlying epidermis each time the insect molts. Gas is exchanged between tissue and environment without involvement of the blood circulatory system. Some insects lack a tracheal system - these insects are restricted to moist habitats.
  • Water conservation is another correlate of a terrestrial lifestyle. Uric acid is primary end product of protein metabolism among insects, and is excreted in a nearly dry, solid form. The major excretory organs are Malpighian tubules, up to 250 pairs in insect hemocoel. Water is resorbed at rectum.
  • Insect flight: Wings are lateral outfoldings of the body wall, and first appeared 300-400 million years ago. There is considerable controversy as to how and why they evolved -- to regulate body temp, stabilize body during jumping, or from gills used in locomotion?
  • Insect social systems are characteristic of Hymenoptera and Isoptera. Colonies include sterile workers & one or more reproductive queens, multiple generations within a colony. Males are all haploid & do no work, & are winged. Males die shortly after mating. (If you are female and have read this, I don't want to hear any snickering in class!)


 Characteristics and habitat

  • Common name is "water bears"
  • Uncertain phylogeny
  • About 400 spp. are named. All of them are small, between 50 - 1200 um in length.
  • Most live in surface films of fresh water on terrestrial plants, e.g., mosses & lichens. Some are marine, living between sand grains.
  • Cuticle is molted, but is made of protein, not chitin
  • Gas exchange occurs across body surface.
  • 4 prs. of clawed appendages, none jointed.
  • No specialized larval stage
  • Some characteristics suggestive of nematodes, such as possessing a pseudocoel, rather than a hemocoel and having constancy of cell numbers in cuticle (eutely).
  • Tardigrades are capable of cryptobiosis, in which they can dehydrate and reduce metabolic rate on exposure to low temperature or desiccation stress. They can remain viable in the cryptobiotic stage up to 10 years. (See Putting Proteins Under Glass, Science 267:1922-1923, March 31, 1995 issue). Interaction of sugars with proteins are protective. There are potential commercial application in increasing shelf-life.


Characteristics and Habitat

  • All are terrestrial, about 100 spp. named
  • Most are in moist habitats and are found in Southern temperate regions, e.g. New Zealand. This restriction to moist habitats may be due to their thin & non waxy cuticle, which permits H2O loss.
  • All are noctural, some carnivore, some herbivore, some omnivores.
  • Carnivores shoot proteinaceous glue from oral protuberances. The prey is entagled in this glue, and the onycophoran bites thru any protective covering. The onychophoran then secretes a poison into the prey, which kills it and then liquifies its tissue.
  • Can grow to 15 cm

Onychophorans share some characteristics with annelids

  • Body wall musculature is smooth, with 3 types of elements -- longitudinal, circular, diagonal
  • Single pair of jaws present
  • All appendages are unjointed
  • Hydrostatic skeleton involved in locomotion, and the outer body wall is deformable.
  • Light receptors are ocelli.

Some characteristics are arthropod-like

  • Jaw musculature is striated
  • Cuticle contains chitin
  • Main body cavity is hemocoel
  • Gas exchange accomplished through spiracles, which open into a tracheal system.
  • Mouth appendages are mandible-like
  • Heart bears ostia
  • Excretory organs resemble green glands of crustacea

Some characteristics are unlike either group

  • Head appendages include one pair each of antennae, jaws, and oral papillae
  • Pairs of unjointed leggs are unlike annelid parapodia.
  • Locomotion dynamics are unlike annelids and arthropods.


General Structure

  • Slender, glassy or shiny appearance.
  • Epidermis secretes a tough but flexible cuticle. Becomes a major factor in treatment of parasitic worms.
  • There are no circular muscles in the body wall. Longitudinal muscles work against the hydrostatic skeleton.
  • Digestive system is complete: food enters mouth and is processed. Wastes eliminated through anus.
  • Body cavity is a pseudocoel.


  • Diecious, females tend to be longer than males.
  • Female reproductive system usually has two ovaries, each continuous with an oviduct and uterus. Male system has a single testis, a seminal vesicle and sperm duct. One or more spicules are present for widening the genital pore of the female.

Parasitic representatives.




Free-living representatives

Vinegar eels


Many characteristics are similar to nematodes

  • Pseucoelomate
  • Sexes separate
  • Worm-like.
  • Eggs fertilized internally.
  • Several molts
  • Possess only longitudinal muscles

Some characteristics are different than nematodes

  • Excretory system is lacking.
  • Details in nervous and reproductive system.
  • No eutely, i.e. constancy in cell numbers.
  • Adults possess non-functional digestive system

 Adults are free-living and aquatic.

  • About 250 spp. are recognized
  • Juveniles are parasitic in insects, absorb dissolved nutrients in the host tissues and fluids.
  • Juveniles penetrate or are ingested by arthropod host

Juveniles can alter arthropod behavior to facilitate transition in life cycle.

  • When ready to emerge from insect, behavior is altered to force insect to 'dive-bomb' into body of water.
  • Insect is drowned & fungi attack cuticle, after which a very long adult emerges.

 Gordius is major species. 


 Generally 1 mm or less in length.

  • Commonly found in marine and freshwater environments. They live interstitially in the spaces between sediment particles.
  • Acoelomate organisms.
  • They feed on detritus, bacteria, diatoms or protozoans, and possess a linear digestive system.
  • There are no specialized respiratory or circulatory systems.
  • The excretory system consists of protonephridia.



  Defining characteristics

  • A series of curved, chitinous, grasping spines on both sides of the head for seizing prey;
  • Lateral stabilizing fins, composed of ectodermal derivatives


  • Free-living marine carnivores
  • Several centimeters in length, not exceeding 15 cm.
  • Most are planktonic, and exhibit diurnal vertical migrations. The reason(s) for the migrations is (are) unknown, but may be for avoidance of predators, increasing the energetic efficiency of feeding and digestion, reducing competition, or achieving dispersal.
  • About 120 species are known.

Nervous system

  • Several ganglia surround the anterior part of the intestine, while there is one posterior ventral ganglion. Sensory and motor nerves extend from ganglia to sensory and muscular systems.
  • Chatognaths bear a pair of small eyes, each composed of 5 pigment-cup ocelli, probably functioning for detection of motion and of changes in light intensity.


  • Chaetognaths are commonly called "arrow worms" because they are substantially longer than they are wide and they possess 1 or 2 pairs of lateral fins and a terminal caudal fin which help stabilize the animal.


  • All individuals are simultaneous hermaphrodites.
  • Self-fertilization has been documented.



 General Characteristics and Habitat

  • Includes "lampshells"
  • Shell valves are dorsal/ventral, unlike Bivalvia (ventral).
  • Superficially resembles bivalved molluscs.
  • Body protected by a pair of convex calcified shells
  • 300 living spp. and almost 20 K in fossil record
  • Lophophore larva is drawn into 2 arms, thus providing increased area for food collection & gas exchange
  • One or 2 metaphridia serve as excretory organs.
  • Blood circulatory system present. There is a well developed heart and one to several contractile vessels. Among brachiopods, hemerythrin is the oxygen-carrying protein, and it is found in the fluid fraction of blood.

May live permanently attached to substrate or in sediment.

  • Attachment organ is pedicle.
  • Protrudes through notch
  • Stalk can be quite long.


 General Characteristics and Habitat

  • Phylum Bryozoa = moss animal.
  • All are colonial spp., in which a single individual will reproduce itself. A colony can consist of up to 2 x 106 zooids. Each zooid in the colony will be small, usually < 1 mm each.
  • All secrete a house around the body. The body is called polypide and the house is called cystis.
  • Bryozoan body wall can regenerate new zooid.
  • Entire polypide periodically degenerates into brown body, which is a dark-pigmented mass. A new polypide will then be produced from cystid. Zooids may go through 4 or more such cycles during life.
  • Lophophores are used for feeding and gas exchange.
  • Funicular cords connect zoiids together.

Number of species:

  • 4 K living spp. are marine.
  • 50 living spp. in freshwater.
  • About 15 K spp. in fossil record.

There are two classes in the phylum.

Class Phylactolaemata (about 50 spp.)

  • All are in freshwater
  • Zooids in a colony are monomorphic.
  • Statoblasts are forms which overwinter.

Class Gymnolaemata

  • Includes most marine spp.
  • Are preyed upon by numerous organisms.
  • Polypides essentially share a common metacoel
  • Zooids are polymorphic. Some are feeding, while others serve to clean or defend colony.

Other Features of Lophophorate Biology

  • Asexual reproduction is common in Bryozoa. It is rare in Phoronida and absent in Brachiopoda
  • Most Brachiopods are dioecious, while a few are monoecious. Sperm & eggs are released, usually out nephridiopore. Fertilization is external.
  • In Bryozoa, colonies are hermaphroditic, but indivs are 1 sex.
  • Phoronids & Bryozoans have U-shaped digestive tract.
  • Some spp. lack complete digestive system -- no anus.


General Characteristics and Habitat

  • 6 K living spp., mostly marine, few estuarine, no freshwater
  • Another 13 K spp. in fossil record. Most of the 20 fossil classes have no extant representativesL
  • Larvae are bilaterally symmetrical
  • Most echinoderms have an internal skeleton composed largely of calcium carbonate (CaCO3) with lesser amounts of MgCO3. The components are individually manufactured in specialized cells

The Water Vascular System (WVS) is unique to Echinoderms

  • WVS is a series of fluid-filled canals derived from 1 of 3 prs. of coelomic compartments.
  • Canals lead to podia, or tube feet.
  • Linked to outside by sieve plate called madreporite.
  • Leads down stone canal to ring canal.
  • Tube feet have longitudinal muscles, but lack circular muscles. The tube feet are extended by pumping fluid in This extends the feet hydraulically. There more may more than 2,000 tube feet in one individual. Tube feet are involved in excretion, locomotion, respiration, circulation

Circulatory System

  • Instead of a true heart, a hemal system is present.
  • The hemal system may be involved in transporting nutrients to gonads.

Class Crinoidea is the oldest extant class with a fossil record that goes back 600 million years. There are 2 modern groups.

  • Stalked crinoids, whose common name is sea lilies. There are about 80 modern spp.
  • Nonstalked, motile feather stars, of which there are about 550 modern spp.
  • All are suspension feeders.
  • Sea lilies are attached to substrate by a stalk. The stalk is flexible, composed of calcium plates. The digestive system is tubular. Sea lilies may have 5 to > 200 flexible arms. Two rows of tubular pinnules extend outward from each arm. Food gets caught in mucus, and then gets flicked into ambulacral grooves. Cilia then transport food to mouth.
  • Feather stars are also called comatulids. They are similar to crinoids, but cirri are found at base of body. Cirri can grip solid objects.

Class Stelleroidea contains all other armed echinoderms

Subclass Ophiuroidea - Brittle stars

  • about 2 K spp., all motile
  • Flexible arms radiate outwards.
  • Regeneration of lost arms fairly routine.
  • Many are deposit feeders which ingest sediment and assimilate organic fraction. Ophiurids can also capture small animals in sediment. Others are suspension feeders. Generally, they feed nocturnally.

Subclass Asteroidea - sea stars.

  • About 1600 living spp., constituting the second largest group in Echinoderms
  • Locomotion is slow, involving the coordinated movement of tube feet which lie in the ambulacral groove.
  • Sea star mouth is directed downward. Food passes upward into a very short esophagus, and then to a lower, i.e. cardiac stomach, which may be everted out during the process of ingestion, The cardiac stomach is confined to central body disc and responsible for .digestion. Above the cardiac stomach is the upper, or pyloric stomach. The pyloric stomach has extensions, called pyloric caeca into arms. These extensions function to secrete enzymes, absorb nutrients and store nutrients.
  • Asteroids are predators on large invertebrates. They will prey on sponges, gastropods, polychaetes. Some eat fish, bivalves, other echinoderms.
  • Many undergo autotomy when disturbed.
  • Asteroids possess non-calcified papulae, which are outfoldings of outer body wall. These papulae are involved in respiration.
  • Pedicellariae also present. Each pedicellaria consists of 2, sometimes 3 movable carbonate ossicles (valves), and generallyfunction in removal of debris. They are also present in Echinoidea, the sea urchins and sand dollars.

Class Concentricycloidea

  • Newly discovered - 1986, in deep water.
  • Common name is sea daisies.
  • Small - < 1 cm in diameter.

Class Echinodea - Sea urchins, heart urchins, sand dollars, biscuits

  • Lack arms entirely.
  • Spines used for protection and sometimes locomotion
  • Body areas containing tube feet are in distinct strips.
  • Tube feet involved in locomotion.
  • Some have oral structure called Aristotle's Lantern
  • Stomach is not protrusible
  • Coelomic fluid carries both food & waste, = primary circulatory fluid

Class Holothuroidea (sea cucumbers).

  • Body wall is highly flexible
  • Bilaterally symmetrical
  • Calcareous ossicles are minute.
  • Adults range from a few cm to 1 meter.
  • Cephalization not pronounced.
  • Oval tube feet are modified as large feathery tentacles.
  • Most are deposit feeders
  • Endowed with internal respiratory trees.

Other features of Echinoderms

Reproduction & development

  • Asexual reproduction found in several groups. Including Asteroids, Echiroids and Holothuroids
  • Sexes usually separate. Most have 5 or multiples of 5 gonads.
  • Fertilization is external.


  Defining Characteristic

  • A conspicuous dorsal extension of the pharynx forms an anterior buccal tube or stomochord.
  • Common name for class Enteropneusta is "acorn worms"
  • 85 species are known.
  • Deuterostome


  • All are marine

Class Enteropneusta

  • Possess a proboscis, which is highly muscular. It is responsible for burrowing and food collection.
  • Form U-shaped burrows.
  • Most are deposit feeders, while some are suspension feeders.

Class Pterobranchia

  • Most are found in deep water
  • Unlike enteropneusts, pterobranchs possess ciliated, anterior tentacles and a U-shaped gut.
  • They also produce rigid tubes in which they reside. Tube secretions are produced by glands on an anterior cephalic shield.


 Nonvertebrate Chordates

  Defining Characteristics of the phylum Chordata

  • Nerve cord is dorsal and hollow
  • The body is supported in at least some stage of development by a stiff rod (the notochord) formed from the roof of the archenteron and running the length of the animal ventral to the nerve cord, from anterior to posterior
  • The pharynx is perforated with numerous ciliated slits (stigmata)

Subphylum Urochordata (sea squirts)

  • Notochord and nerve cord are found only in the larval stage, being reabsorbed at metamorphosis.
  • Contains three classes, Ascidiacea, Larvacea, Thaliacea, of which Ascidiacea is most common (90%).
  • Marine species, found in both shallow and deep water.
  • Most are sessile, bag-like with a secreted protective tunic composed of protein and a polysaccharide.
  • Pharyngeal basket filters water, food particles put into mouth, while waste water, waste materials, feces, and gametes exit via atrial siphon.
  • Among colonial species, there may be one atrial siphon shared by several animals.
  • Association with Chordates becomes apparent when the larvae, known as tadpoles, are examined.
  • Reproduction is varied. Among solitary ascidians, fertilization is usually external, where gametes or larvae are discharged through the atrial siphon.

Subphylum Cephalochordata (commonly called lancelets or amphioxus)

  • Defining characteristics include a notochord which extends beyond the nerve cord to the anterior end of the animal, and the notochord is contractile, formed as a longitudinal series of flattened discs containing thick myosin filaments.
  • Reside in marine environments, and are usually less than 10 cm long.
  • Feeding involves capture of microscopic food particles on mucous sheets. Captured food then enters the gut as a mucous string. Water flow is created by cilia on the pharynx, not be muscular activity.
  • Notochord persists throughout life.


Groovy Web Sites

Entomology Index of Internet Resources

Integrated taxonomic information system

E-quarium at Monterey Bay Aquarium