Animals that lack a backbone
Sponges; simple, sessile animals that lack true tissues
Corals/Jellies/Hydras; animals with a distinctive body plan including a gastrovascular cavity with a single opening, serving as both mouth and anus.
A single invertebrate species that consists of a few thousand cells arranged in a double-layered plate, able to reproduce by fission or budding.
A microscopic animal consisting of thirteen segments covered in plates, with a retractable, spine-tipped mouth.
Flatworms with bilateral symmetry and a central nervous systems, though lacking a body cavity or circulatory organs.
Microscopic animals with specialized organ systems, including an alimentary canal, that feed microorganisms suspended in water.
Bryozoans; sessile animals that live in colonies and are covered by a tough exoskeleton.
Marine worms that live in tunnels in the seafloor, extending tentacles outside to trap food particles.
Lamp shells; mollusc-like animals with a unique stalk that anchors them to their substrate.
Proboscis/ribbon worms; worms that extend a unique proboscis to catch prey, and, like flatworms, lack a true coelom, though they also possess an alimentary canal
Worms possessing curved hooks located on the proboscis at the anterior end of the body, whose larvae develop in arthropods and adults live in vertebrates, some manipulating their hosts in certain ways.
Diploblastic, early-diverging animals similar to cnidarians that possess a set of eight distinctive 'combs' of cilia that propel them through water, with the unique method of covering prey with sticky threads derived from specialized cells on the tentacles.
Animals possessing a soft body that in most species is covered by a hard shell.
Segmented worms that are distinguishable by their unique body segmentation.
Microscopic animals that inhabit the deep-sea bottom, able to telescope its head, neck, and thorax in out of a lorica, a pocket formed by six plates surrounding the abdomen.
Worms with a large, rounded proboscis at the anterior end, that were possibly the major predators of the Cambrian period.
Roundworms; Enormously abundant parasitic worms with a tough cuticle that coats the body.
The vast majority of known animals, possessing a segmented exoskeleton and jointed appendages.
A tiny, vase-shaped species with a unique body plan and reproductive cycle, in which males impregnate developing female embryos, who escape and settle on a lobster, releasing their offspring.
"Water Bears"; Microscopic animals with a rounded shape, stubby appendages, and a lumbering gait, that can survive extremely harsh conditions through entering dormancy.
Velvet worms; Humid-environment worms originating in the Cambrian explosion, possessing a fleshy antennae and several dozen pairs of saclike legs.
Deuterostome animals similar to chordates, possessing gill slits and dorsal nerve chord, and known widely as 'acorn worms'.
Aquatic animals that display radial symmetry as adults, moving and feeding by using a network of internal canals to pump water to different parts of the body.
Animals possessing a backbone, though three species (tunicates, lancelets, and hagfishes) are exempt.
Animals that capture food particles suspended in the water that passes through their body, which typically resembles a sac perforated with pores.
A central cavity of suspension feeders into which water drawn.
A large opening into which water from the spongocoel flows.
Collar cells that line the interior of the spngocoel or internal water chambers, generating a water current using flagella and then trapping food particles by phagocytosis.
A gelatinous region separating the two layers of a sponge.
Pseudopodia-using cells that wander the mesohyl and are responsible for digestion of food, manufacturing of tough skeletal fibers, and other jobs.
An individual able to function both as a male and female in sexual reproduction, by producing both sperm and eggs.
Cylindrical cnidarian forms that adhere to the substrate by the aboral end of the mouth and extend their tentacles, waiting for prey.
A flattened, mouth-down version of the polyp, able to move freely in water by a combination of passive drifting and contractions of its bell-shaped body.
Unique cells that function in defense and the capture of prey in cnidarians.
A class of cnidarian alternating between a colonial polyp and medusa form.
A free-swimming class of cnidarian with a reduced polyp stage.
A box-shaped class of cnidarian with complex eyes
A sessile, colonial class of cnidarian with no medusa stage.
A solid ciliated larval stage of the hydrozoan life cycle.
The best-known turbellarians, abundant in unpolluted ponds or streams.
A free-living, marine class of platyhelminthe that can reproduce asexually by regeneration.
A parasitic class of platyhelminthe with a simple life history where ciliated larva starts infection on the host, usually on the external surface of fishes.
Flukes; a parasitic class of platyhelminthe that possesses two suckers to attach to a host, usually a vertebrate, with an intermediate host as part of the life cycle.
Tapeworms; a parasitic class of platyhelminthe possessing a scolex that attaches to the host, proglottids that produce eggs and break off after reproduction, no head or digestive system, and a life cycle with one or more intermediate hosts.
A muscular organ extending from a turbellian's ventral side, that sucks small pieces of food into gastrovascular cavity.
A dense cluster of nerve cells located at the anterior end of the worm.
A digestive tube with a separate mouth and anus.
A type of reproduction in which females produce more females from unfertilized eggs.
Closed Circulatory System
An anatomical feature found in the phylum Nemertea in which the blood is contained in vessels is therefore distinct from the fluid in the body cavity.
The part of a mollusc that contains most internal organs.
A fold of tissue in molluscs that drapes over the visceral mass and secretes a shell.
A water-filled chamber that houses the gills, anus, and excretory pores of a mollusc.
A straplike rasping organ used by molluscs to scrape up food.
A free-swimming, ciliated larval stage of many worms and some molluscs
A class of molluscs that have a shell divided into eight overlapping plates, a foot used for locomotion, a radula, and no head.
A class of molluscs with an asymmetrical body, usually with a coiled and reduced or absent shell, using a foot for locomotion and possessing a radula.
In gastropods, a developmental process in which the visceral mass rotates up to 180°, causing the animal's anus and mantle cavity to be positioned above its head.
A suspension-feeding class of molluscs with a shell divided into two halves, hinged at the mid-dorsal line, with no distinctive head or radula, paired gills, and whose mantle forms siphons.
A class of molluscs with a head surrounding by grasping tentacles, usually with suckers, and locomotion via jet propulsion using a siphon made from the foot.
Shelled cephalopods that were the dominant invertebrate marine predators until their extinction at the end of the Cretaceous period.
A class of annelids with a reduced head, no parapodia, and chaeta.
A pair of paddle-like appendages covered with setae found in annelids that provide more surface area for respiration by diffusion
A stiff chitinous seta or bristle found on annelids.
A tube-dwelling, free-living class of annelids with a well-developed head, and parapodia with chaetae on each segment.
A flattened class of annelids, parasitic, predatory, and scavenging, with reduced coelom and segmentation, absent chaetae, and suckers at both ends.
A type of tubular excretory system that has internal openings that collect body fluids, found in most annelids.
Early arthropods with pronounced segmentation, but little variation between segments.
A protein- and chitin-constructed cuticle covering the body of an arthropod.
Ecdysis; an energetically expensive process undergone by arthropods that shed their exoskeletons and produce a new one.
Open Circulatory System
A circulatory system found in arthropods that allows the blood to flow out of the blood vessels and into various body cavities so that the cells are in direct contact with the blood
Arthropods with a one- or two-part body and six pairs of appendages
A terrestrial class of arthropods with a distinct head bearing antennae and chewing mouthparts, divided into millipedes and centipedes.
A class of arthropods with a body divided into the head, thorax, and abdomen, possessing antennae, with mouthparts modified for chewing, sucking, or lacking, three pairs of legs, and usually two pairs of wings.
Arthropods with a one- or two- part body, possessing antennae, chewing mouthparts, and three or more pairs of legs.
Clawlike feeding appendages possessed by cheliceriformes
Water scorpions; the earliest cheliceriforms
An excretory organ that is unique to insects, empties into digestive tract and removes nitrogenous wastes from the hemolymph, also plays a role in osmoregulation.
A network of breathing tubes that extend throughout the body of most terrestrial arthropods
One of a pair of nerve cell clusters that serve as a primitive brain at the anterior end of some invertebrates, such as annelids
A type of development in certain insects, such as grasshoppers, in which the young (called nymphs) resemble adults but are smaller and have different body proportions. The nymph goes through a series of molts, each time looking more like an adult, until it reaches full size.
A type of insect development in which the larvae look and act nothing like their parents and also feed in completely different ways
A member of one of the largest groups of crustaceans, which includes terrestrial, freshwater, and marine species. Among the terrestrial isopods are the pill bugs, or wood lice.
A group of large crustaceans that includes shrimp, lobster, and crabs.
Minute shrimp-like crustaceans that are the most common zooplankton in estuarine waters
Water Vascular System
A network of hydraulic canals unique to echinoderms that branches into extensions called tube feet, which function in locomotion, feeding, and gas exchange
Extensions of echinoderms water vascular system that stick out from the body and function in movement and obtaining food
A sievelike structure through which the water vascular system of an echinoderm opens to the outside
A class of echinodermata possessing a star-shaped body with multiple arms and a mouth directed to the substrate.
A class of echinodermata with a distinct central disk, long flexible arms, and whose tube feet lack suckers.
A spherical or disk-shaped class of echinodermata lacking arms, and possessing five rows of tube enabling slow movement, and a mouth ringed by a complex, jaw-like structure.
A class of echinodermata possessing feathered arms surrounding an upward-pointed mouth
A class of echinodermata possessing a cucumber-shaped body, five rows of tube, additional tube feet modified as feeding tentacles, a reduced skeleton, and no spines.
A class of disk-shaped echinodermata ringed with small spines, possessing an incomplete digestive system, and living on submerged wood.