aboral Opposite end or side from which the mouth is located.

agar A red algal gum that has many uses including meat packaging and microbiological media.

annulation Marked or formed of rings or segments.

antenna (plural antennae). In polychaete annelids, a slender sensory projection arising from the top, sides or front of the prostomium (head area), often in pairs. In arthropods, the first (and sometimes second) head appendage.

aperture In snails, the opening in the shell from which the animal’s body protrudes.

atrial cavity In tunicates, the central body cavity.

avicularium (plural avicularia). In bryozoans, a specialized zooid that resembles the beak of a bird.

benthic Referring to the sea floor.

bioturbating Reworking and aerating sediments via the activities of living organisms.

branchia (plural branchiae). Structure, usually with blood vessels, that functions as a gill.

carapace Hard shield or section of the exoskeleton on the back of a crab or shrimp that protects the head and thorax.

caudal fin A propulsive and stabilizing structure at the rear of fish.

cerata (singular ceras). In nudibranchs (sea slugs) and their relatives, fleshy processes on the back that contain diverticula (branches) of digestive glands.

cf. Species unknown or new but most closely compared with that listed.

chaeta (plural chaetae). In polychaete annelids, a chitinous bristle emerging from or embedded in the parapodium (appendage). Seta (setae) is an equivalent, outdated spelling.

chaetiger Any segment of a polychaete annelid that bears chaetae (bristles). Setiger is an equivalent, outdated spelling.

cheliped In crabs, shrimps and their relatives, a leg with a pincer at its free end.

chitin A polysaccharide (carbohydrate whose molecules consist of long chains of simple sugars) forming the major constituent of an arthropod exoskeleton, a polychaete annelid worm bristle or some polychaete annelid tubes.

chloroplast A small organelle, containing a green pigment responsible for light absorption, within a cell undergoing photosynthesis.

chondrophore In bivalve molluscs, a spoon-shaped structure, often projecting from the hinge plate.

cilia Microscopic hair-like processes used in locomotion, food gathering and other functions.

cirrus (plural cirri). Soft, fleshy projection ranging in shape from hair-like, finger-like, cylindrical to leaf-like; generally sensory in nature.

cnidocyte (nematocyst). In sea anemones, corals, jellies and their relatives, the microscopic stinging organ usually found on the tentacles.

collar cells In sponges, the flagellate (long lash-like appendage) cells that line the body cavities.

columella In many snails, the central axis of the shell around which the shell and the body of the snail spirals or coils.

commensalism An association between two species that live together, which benefits individuals of one species without harming those of the other.

ctenes In comb jellies (sea gooseberries), the bands of fused cilia that form individual comb plates, which, in long series, form the eight characteristic combs defining the animal.

demersal Being or living near the sea bottom.

detritus Debris containing organic matter, often of decomposed organisms, recycled as a major food source for many organisms.

dorsal fin A stabilizing structure on the back of fish.

elytra (singular elytron). In some polychaete annelids, a shield-like plate on the back of the worm.

elytron (plural elytra). A shield-like scale or plate on the dorsum (back) of scaleworms, polychaete annelids; notably in pairs.

elytrophore A stalk that attaches the elytron to the back of the scaleworm.

epidermis Outer cell layer of the skin.

epifauna Benthic organisms living on or above the surface of the sediment.

epigamy In some polychaete annelids, a structural modification of an entire adult individual into an epitoke or reproductive stage, ready to leave the bottom for swarming and spawning.

epiphyte A plant or alga growing on, but not parasitic on, another.

epitoke In some polychaete annelids, a structurally modified individual, pelagic sexual stage, that leaves the bottom to reproduce; includes epigamous epitokes and schizogamous epitokes.

exoskeleton The chitinous, rigid outer covering of a crab, shrimp or other arthropod.

forma Of a particular morphology but without a particular ecological or genetic rationale or reason.

fucan A sulphated polysaccharide (carbohydrate whose molecules consist of long chains of simple sugars) that is a common structural component of the cell wall of many brown algae.

gamete A mature germ cell, i.e. egg or sperm, able to unite with another cell in sexual reproduction.

gametophyte A gamete producing form of an organism that has alternation of generations with the asexual form.

gonangium (plural gonangia). In hydroids (sea firs), a polyp for production of medusae.

hemoglobin A red oxygen-carrying pigment, containing iron and protein, present in red blood cells or body fluids.

heteromorphic Of dissimilar forms, e.g. existing in different forms in a life cycle.

heteronereid Modified pelagic, reproductive stage or epitoke of a mature sea-nymph, polychaete annelid.

holdfast In large algae, a root-like structure that seaweeds use to attach to the substrate or other solid objects.

holistic Describes the view of an entire system as a whole rather than by its separate parts.

hydranth In colonial hydroids (sea firs), a polyp designed for feeding.

infauna Benthic orgamisms living within the sediment.

introvert In peanut worms, a portion of the body that can be retracted by being pulled inside itself.

lophophore In moss animals (bryozoans), lampshells and phoronids, a circular or horseshoe-shaped fold or ridge on the body wall that bears ciliated tentacles used for respiration and food collection.

mantle In molluscs, the interior sheet of tissue that encloses the rest of its soft body. The shell (or shells), if present in the mollusc, are secreted by the edge of the mantle.

manubrium In jellies, the stalk on which the mouth is located.

medusa A jelly. The free-swimming life history stage of some cnidarians. (The term jellyfish is outdated and considered a misnomer.)

moult In arthropods, the cast-off exoskeleton resulting from a growth increment.

neurochaeta In polychaete annelids, a chaeta (bristle) protruding from the neuropodium.

neuropodium (plural neuropodia). In polychaete annelids, the lower lobe of the parapodium (appendage).

notochaeta (plural notochaetae). In polychaete annelids, a bristle protruding from the notopodium.

notochord Particularly in larval tunicates (sea squirts), a primitive type of skeletal rod.

notopodium (plural notopodia). In polychaete annelids, the upper lobe of the parapodium (appendage).

ocellus A simple eye or eyespot.

operculum In most snails, the trap door attached to the foot, which covers and seals off the shell opening. Present, in modified form, in some polychaete annelids.

oral disc In sea anemones and their relatives, the rounded top, ringed with tentacles, that contains the central mouth/anus.

osculum (plural oscula). In sponges, the excurrent opening by which water is pumped from an individual cell.

ossicle In echinoderms, a calcareous skeletal structure, often plate-like or spine-like.

palea (plural paleae). In some polychaete annelids, a specialized, modified chaeta (bristle), broad and flat or ornate and hooked, located near the head.

palp In some polychaete annelids, one of a set of paired structures arising from the specific areas of the head or prostomium: short, conical or cushion-like sensory structures in some; long, grooved feeding structures in others.

papilla (plural papillae). A tiny, fleshy projection from the body wall or other structures, usually sensory in nature.

papulae In sea stars, the thin-walled, sac-shaped gills that form as out-pocketings of the body wall on the back (aboral) surface of the animal.

parapodium (plural parapodia). In polychaete annelids, the flap-like appendages on each side of most segments, from which chaetae (bristles) arise.

pectoral fins A pair of stabilizing and propulsive structures on the belly, one on each side immediately behind the head of a fish.

pedicellaria In sea stars and sea urchins, tiny pincer-like structures on the body’s surface.

peduncle In lampshells, a stalk that anchors the animal to the substrate.

pelagic Belonging to the water column of the ocean.

pelvic fins A pair of stabilizing structures located on the belly area of a fish.

periostracum In molluscs, the organic material, often fibrous, that coats the outside of the shell.

photosynthesis The process by which the energy of sunlight is used by organisms (especially plants) to synthesize or create carbohydrates from carbon dioxide and water.

plankton Free-floating aquatic organisms whose mobility is essentially controlled by currents.

pleopod In crabs, shrimps and their relatives, a paired, two-branched appendage found on the ventral (under) side of the abdomen.

polybostrichus In some necklace-worms (polychaete annelids), a male version of a stolon.

polyp In cnidarians, an individual, often part of a colony, with one end comprising a mouth surrounded by tentacles and the other end attached to the substrate.

proboscis (plural proboscises). In ribbon worms, an anterior cylindrical sensory, defensive and offensive organ that can evert itself. In some polychaete annelids, the anterior, eversible part of the digestive tract.

prostomium In polychaete annelids, the head, without segments and anterior to the mouth; sometimes bearing eyes, antennae, and/or palps.

proventricle In some polychaete annelids, a muscular, glandular, gizzard-like tube forming part of the digestive tract posterior to the proboscis; involved in food processing.

radiole In sabellid and serpulid tubeworms (polychaete annelids), one of several to many feather-like and spoke-like branches of the tentacular crown.

radula In snails, limpets and nudibranchs (sea slugs), a tooth-like file, located in the mouth, used to rasp food from hard surfaces.

rays In sea stars, the appendages or “arms” radiating from the central disc.

rhinophore In nudibranchs (sea slugs) and bubbleshells, a paired sensory organ located on the head.

rhizome A root-like stem bearing both roots and shoots.

rostrum In shrimps and some other arthropods, the spine-like anterior projection on the carapace.

sacconereis In some necklace-worms (polychaete annelids), the female stolon.

schizogamy In some polychaete annelids, a structural modification of part of an adult individual by budding off sexual epitokes, or reproductive stages (i.e., stolons), that leave the bottom for swarming and spawning.

scyphistoma In some jellies, a sessile polyp that produces and ejects young medusae (jellies).

siphon Either of two tubes in bivalve molluscs and tunicates: the inhalent tube draws water into the mouth and gills; the exhalent tube ejects wastewater. In some snails, the siphon is a single tube that is sensory.

siphonal canal In some coiled snail species, a canal, located at the extreme end of the aperture or opening, from which the siphon protrudes.

sp. Species identity undetermined.

spicule In sponges and some other animals, the skeletal building block that stiffens the body.

sp. nov. A species that is not yet formally described.

spore Specialized reproductive cell of many plants, algae and micro- organisms.

spp. More than one species undetermined.

ssp. Subspecies.

stigmata In tunicates (sea squirts), perforations in the pharynx (internal filtering sac).

stolon In some polychaete annelids, a secondary individual, budded off from a parent individual or stock, that forms a pelagic reproductive, sexual stage.

stylet In some snails and some ribbon worms, a slender pointed structure for piercing prey.

taxonomy The science of classification of living and extinct organisms; in specific terms the identification, describing and naming of species.

tentacular crown In sabellid and serpulid tubeworms (polychaete annelids), the array of feather-like radioles on the head used for feeding and respiration.

tentilla (singular tentillum). In some cnidarians, the contractile branches on a long, hollow feeding tentacle that bear stinging cells.

test In sea urchins and sand dollars, the rigid, calcareous protective container formed from fused ossicles.

tubercle A small bump, or knob-like projection, on the skin of some invertebrates.

tunicin In tunicates (sea squirts), the leathery outer covering of the body.

umbilicus In snails, the hole or opening in the shell that is visible at the base of the columella (central axis). The hole is formed because the whorls are not closely wound against each other at either end of the axis.

var. Variety or subspecies.

villi Numerous short slender hair-like projections on some membranes.

whorl In many snails, a turn or twist of the shell spire. The largest and newest whorl is the body whorl, which provides the aperture through which the foot and head protrude.

zooid In bryozoans (moss animals), colonial tunicates (sea squirts) and hydroids (sea firs), individual members of a colony that are structurally continuous, usually in box-like, cup-like or tube-like units.