5.8.9: Key Terms

amoebocyte

sponge cell with multiple functions, including nutrient delivery, egg formation, sperm delivery, and cell differentiation

Annelida

phylum of vermiform animals with metamerism

archenteron

primitive gut cavity within the gastrula that opens outward via the blastopore

Arthropoda

phylum of animals with jointed appendages

biramous

referring to two branches per appendage

captacula

tentacle-like projection that is present in tusks shells to catch prey

cephalothorax

fused head and thorax in some species

chelicera

modified first pair of appendages in subphylum Chelicerata

choanocyte

(also, collar cell) sponge cell that functions to generate a water current and to trap and ingest food particles via phagocytosis

Chordata

phylum of animals distinguished by their possession of a notochord, a dorsal, hollow nerve cord, an endostyle, pharyngeal slits, and a post-anal tail at some point in their development

clitellum

specialized band of fused segments, which aids in reproduction

Cnidaria

phylum of animals that are diploblastic and have radial symmetry

cnidocyte

specialized stinging cell found in Cnidaria

conispiral

shell shape coiled around a horizontal axis

corona

wheel-like structure on the anterior portion of the rotifer that contains cilia and moves food and water toward the mouth

ctenidium

specialized gill structure in mollusks

cuticle (animal)

the tough, external layer possessed by members of the invertebrate class Ecdysozoa that is periodically molted and replaced

cypris

larval stage in the early development of crustaceans

Echinodermata

phylum of deuterostomes with spiny skin; exclusively marine organisms

enterocoelom

coelom formed by fusion of coelomic pouches budded from the endodermal lining of the archenteron

epidermis

outer layer (from ectoderm) that lines the outside of the animal

extracellular digestion

food is taken into the gastrovascular cavity, enzymes are secreted into the cavity, and the cells lining the cavity absorb nutrients

gastrodermis

inner layer (from endoderm) that lines the digestive cavity

gastrovascular cavity

opening that serves as both a mouth and an anus, which is termed an incomplete digestive system

gemmule

structure produced by asexual reproduction in freshwater sponges where the morphology is inverted

hemocoel

internal body cavity seen in arthropods

hermaphrodite

referring to an animal where both male and female gonads are present in the same individual

invertebrata

(also, invertebrates) category of animals that do not possess a cranium or vertebral column

madreporite

pore for regulating entry and exit of water into the water vascular system

mantle

(also, pallium) specialized epidermis that encloses all visceral organs and secretes shells

mastax

jawed pharynx unique to the rotifers

medusa

free-floating cnidarian body plan with mouth on underside and tentacles hanging down from a bell

mesoglea

non-living, gel-like matrix present between ectoderm and endoderm in cnidarians

mesohyl

collagen-like gel containing suspended cells that perform various functions in the sponge

metamerism

series of body structures that are similar internally and externally, such as segments

Mollusca

phylum of protostomes with soft bodies and no segmentation

nacre

calcareous secretion produced by bivalves to line the inner side of shells as well as to coat intruding particulate matter

nauplius

larval stage in the early development of crustaceans

nematocyst

harpoon-like organelle within cnidocyte with pointed projectile and poison to stun and entangle prey

Nematoda

phylum of worm-like animals that are triploblastic, pseudocoelomates that can be free-living or parasitic

Nemertea

phylum of dorsoventrally flattened protostomes known as ribbon worms

osculum

large opening in the sponge’s body through which water leaves

ostium

pore present on the sponge’s body through which water enters

oviger

additional pair of appendages present on some arthropods between the chelicerae and pedipalps

parapodium

fleshy, flat, appendage that protrudes in pairs from each segment of polychaetes

pedipalp

second pair of appendages in Chelicerata

pilidium

larval form found in some nemertine species

pinacocyte

epithelial-like cell that forms the outermost layer of sponges and encloses a jelly-like substance called mesohyl

planospiral

shell shape coiled around a vertical axis

planuliform

larval form found in phylum Nemertea

polymorphic

possessing multiple body plans within the lifecycle of a group of organisms

polyp

stalk-like sessile life form of a cnidarians with mouth and tentacles facing upward, usually sessile but may be able to glide along surface

Porifera

phylum of animals with no true tissues, but a porous body with rudimentary endoskeleton

radula

tongue-like organ with chitinous ornamentation

rhynchocoel

cavity present above the mouth that houses the proboscis

schizocoelom

coelom formed by groups of cells that split from the endodermal layer

sclerocyte

cell that secretes silica spicules into the mesohyl

seta/chaeta

chitinous projection from the cuticle

siphon

tubular structure that serves as an inlet for water into the mantle cavity

spicule

structure made of silica or calcium carbonate that provides structural support for sponges

spongocoel

central cavity within the body of some sponges

trochophore

first of the two larval stages in mollusks

uniramous

referring to one branch per appendage

veliger

second of the two larval stages in mollusks

water vascular system

system in echinoderms where water is the circulatory fluid

zoea

larval stage in the early development of crustaceans