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Porifera

Phylum of sponges; simplest multicellular animals with pores, choanocytes, and no true tissues or organs.

Ostia

Tiny pores in sponges where water enters the body.

Osculum

Large opening in sponges where water exits.

Spongocoel

Hollow central cavity of a sponge where water passes through.

Choanocytes

Flagellated collar cells in sponges that create water currents and trap food.

Archaeocytes

Amoeboid sponge cells that digest food, remove wastes, and can form reproductive or support cells.

Spicules

Hard support structures in sponges made of calcium carbonate or silica.

Spongin

Flexible protein fibers that support the body of some sponges.

Calcarea

Sponge class with calcium carbonate spicules.

Demospongiae

Largest sponge class; usually has spongin and/or silica spicules.

Hexactinellida

Glass sponges with six-rayed silica spicules.

Cnidaria

Phylum with radial symmetry, tentacles, cnidocytes, and a gastrovascular cavity.

Cnidocytes

Stinging cells of cnidarians used for defense and capturing prey.

Nematocyst

Stinging capsule inside a cnidocyte.

Gastrovascular cavity

Blind digestive cavity with one opening for both food intake and waste exit.

Polyp

Sessile body form of cnidarians, usually tube-shaped and attached to a surface.

Medusa

Free-swimming bell-shaped body form of cnidarians.

Hydra

Freshwater cnidarian usually seen in polyp form.

Obelia

Colonial cnidarian that has both polyp and medusa stages.

Coral

Cnidarian polyp that secretes calcium carbonate and may form reefs.

Platyhelminthes

Phylum of flatworms; soft-bodied, dorsoventrally flattened, and acoelomate.

Acoelomate

Animal body plan with no body cavity.

Turbellaria

Class of mostly free-living flatworms such as planarians.

Trematoda

Class of parasitic flukes, usually endoparasitic.

Cestoda

Class of tapeworms; endoparasitic and usually lack a digestive tract.

Monogenea

Class of mostly ectoparasitic flatworms found on fishes, amphibians, and turtles.

Planaria

Free-living flatworm commonly used as a representative of Turbellaria.

Fasciola

Liver fluke; a parasitic flatworm under Trematoda.

Schistosoma

Blood fluke; a parasitic flatworm under Trematoda.

Taenia

Tapeworm genus under class Cestoda.

Scolex

Attachment head of a tapeworm with suckers or hooks.

Proglottids

Repeating reproductive segments of a tapeworm.

Nematoda

Phylum of roundworms with a cuticle, pseudocoelom, and complete digestive tract.

Pseudocoelom

False body cavity not completely lined by mesoderm.

Cuticle

Tough protective outer covering of nematodes.

Ascaris lumbricoides

Parasitic roundworm commonly studied as a representative nematode.

Longitudinal muscles

Muscles running lengthwise; the main body wall muscles of nematodes.

Sinusoidal movement

Whip-like side-to-side movement seen in nematodes.

Annelida

Phylum of segmented worms with true coelom and repeated body segments.

Segmentation

Division of the body into repeated sections or segments.

Coelom

True body cavity completely lined by mesoderm.

Polychaeta

Class of mostly marine annelids with parapodia and many setae.

Oligochaeta

Subclass of annelids including earthworms; have fewer setae.

Hirudinea

Subclass of annelids including leeches; usually have suckers.

Setae

Bristle-like structures used by annelids for movement or anchoring.

Parapodia

Fleshy appendages in polychaetes used for movement and gas exchange.

Clitellum

Thickened reproductive band in earthworms and other clitellates.

Metanephridia

Excretory organs of annelids.

Crop

Food storage organ in earthworms.

Gizzard

Muscular grinding organ in earthworms.

Leech

Annelid under Hirudinea with anterior and posterior suckers.

Nereis

Sandworm; a polychaete annelid with parapodia.

Mollusca

Phylum of soft-bodied animals with mantle, muscular foot, and visceral mass.

Mantle

Tissue fold in mollusks that secretes the shell and forms the mantle cavity.

Muscular foot

Main locomotor structure of mollusks.

Visceral mass

Region of mollusk body containing most internal organs.

Radula

Abrasive tongue-like feeding organ in most mollusks, absent in bivalves.

Polyplacophora

Molluscan class including chitons with eight limy plates.

Bivalvia

Molluscan class with two shells; includes clams, oysters, mussels, and scallops.

Gastropoda

Molluscan class including snails and slugs; often has coiled shell and torsion.

Cephalopoda

Molluscan class including octopus, squid, cuttlefish, and nautilus; has arms or tentacles.

Scaphopoda

Molluscan class including tusk shells; shell is open at both ends.

Chiton

Polyplacophoran mollusk with eight dorsal shell plates.

Torsion

Gastropod developmental process where the mantle and visceral mass rotate.

Dentalium

Tusk shell genus under Scaphopoda.

Arthropoda

Phylum with jointed appendages, chitin exoskeleton, segmented body, and molting.

Exoskeleton

External skeleton that supports and protects arthropods.

Chitin

Strong material that makes up the arthropod exoskeleton.

Ecdysis

Molting process where arthropods shed their exoskeleton to grow.

Tagmatization

Fusion or grouping of body segments into functional regions.

Hemocoel

Main body cavity in arthropods containing hemolymph.

Open circulatory system

Circulatory system where blood-like fluid is not always contained in vessels.

Chelicerata

Arthropod subphylum with chelicerae; includes spiders, scorpions, and horseshoe crabs.

Chelicerae

First pair of appendages in chelicerates used for feeding.

Arachnida

Class of chelicerates with four pairs of legs and no antennae.

Myriapoda

Arthropod group including centipedes and millipedes.

Diplopoda

Class of millipedes; usually has two pairs of legs per segment.

Chilopoda

Class of centipedes; usually has one pair of legs per segment.

Crustacea

Mostly aquatic arthropods with two pairs of antennae and biramous appendages.

Hexapoda

Arthropod group with three pairs of legs; includes insects.

Insecta

Class of arthropods with head, thorax, abdomen, and three pairs of legs.

Echinodermata

Phylum of marine spiny-skinned animals with water vascular system and tube feet.

Water vascular system

Hydraulic system in echinoderms used for movement, feeding, and respiration.

Tube feet

Small extensions of the water vascular system used for movement and attachment.

Madreporite

Sieve-like opening where water enters the echinoderm water vascular system.

Stone canal

Canal connecting the madreporite to the ring canal in echinoderms.

Ring canal

Circular canal around the mouth area of echinoderms.

Radial canal

Canal extending into each arm of an echinoderm.

Ampullae

Bulb-like structures that control movement of tube feet.

Calcareous ossicles

Calcium-based skeletal plates in echinoderms.

Pentamerous radial symmetry

Five-part radial symmetry seen in adult echinoderms.

Oral surface

Surface of an echinoderm where the mouth is located.

Aboral surface

Surface opposite the mouth in echinoderms.

Crinoidea

Echinoderm class including sea lilies and feather stars.

Stelleroidea

Echinoderm group including sea stars and brittle stars.

Asteroidea

Subclass of sea stars with arms not sharply distinct from the central disc.

Ophiuroidea

Subclass of brittle stars with long flexible arms and small central disc.

Echinoidea

Echinoderm class including sea urchins, sand dollars, and sea biscuits.

Holothuroidea

Echinoderm class including sea cucumbers.

Aristotle’s lantern

Feeding structure in echinoids used for scraping or collecting food.