ampullae of Lorenzini: natural electrical detectors located in the heads of sharks and rays that are sensitive to the electronic signals emitted by potential prey.

Aristotle's lantern: a feeding structure of echinoids that is formed from several calcareous elements and includes the jaws.

baleen: the comb-like fibrous plates hanging from the upper jaw of some whales, that are used to sieve food from seawater, often called whalebone.

barbel: a slender, fleshy protruberance on the lower jaw of some fish and sharks, equipped with sensory and chemical receptors and used to locate food.

benthic: living on or near the seabed or under the sediment

bilaterally symmetrical: animals which can be divided into two equal halves by a line drawn down the centre.

bivalve: an animal with a shell in two parts hinged together e.g. mussels and clams.

bryozoans: minute sedentary aquatic animals superficially resembling coelenterate polyps, usually living in colonies and having a calcareous exoskeleton.

calcareous: rich in calcium salts, usually calcium carbonate, generally hard such as a sea shell.

caudal: pertaining to the tail region

caudal fin: tail fin

chitin: a horny fingernail-like substance usually tough and brown that forms the sucker rings, hooks and beaks of cephalopods, l the trapdoor of a snail shells and most of the hard parts of arthropods.

cirrus (pl.=cirri): a limb of a barnacle that extends and contracts during feeding also a slender jointed appendage that projects from the base of a feather star and is used for attachment or locomotion; hair-like or finger-like tactile or sensory processes on many animals and plants.

claspers: the modified inner edges of the pelvic fins in male sharks and rays, used for the transfer of sperm to the female.

cloaca: a common opening for the reproductive, excretory and digestive tracts.

commensal: living: together for mutual benefit in a less intimate association than symbiosis; a close association between species where one (the commensal) gains benefit while the other (the host) is not adversely affected.

cuttlebone: calcareous supporting plate in the upper side of the mantle of cuttlefish.

cusp: a projection (point) on a tooth; many teeth have just one large cusp but some have additional side cusps.

demersal: found at the bottom or near the bottom of the sea or other aquatic habitat.

denticles: the tooth like scales of sharks and rays.

dorsal: the upper surface of the body or head

dorsal fins: the unpaired fin or fins along the upper surface of the back

endemic species: restricted to a particular geographic region and thought to have originated there.

flagellum (pl.=flagella): a long whip-like process the extends from the surface of the call.

flukes: in cetaceans the horizontally flattened tail.

gastropod: a class of molluscs which includes snails slugs and sea-hares, having a distinct head, with eyes and tentacles and often have a single shell.

hermaphrodite: a plant or animal with both male and female sexual organs.

krill: tiny shrimp-like crustaceans that occur in the open seas and are a major part of the diet of the baleen whales.

larvae: early young that are completely unlike the adults.

mantle: a type of tissue on the body surface, which only occurs in molluscs, which secretes and protects the shell.

medusa (pl= medusae): a free swimming animal shaped like a saucer, with tentacles projecting from the underside.

melon: in many toothed whales the bulging forehead containing oil, muscles and nasal air sacs and passages, believed to be used in focusing sounds for echolocation.

nematocyst: a stinging cell of a cnidarian.

oophagy, oviphagous: egg eating; in some shark species the older embryos feed on unfertilised eggs and smaller embryos within the uterus.

oscule: the exhalant opening of a sponge.

oviparous: egg laying; little or no development occurs within the mother's body, instead embryos develop outside and each egg eventually hatches to a young animal.

ovoviviparous: giving birth to well developed young from eggs that hatch within the mother's body. The young are almost exact replicas of the adult.

pectoral fins: paired fins located just behind or below the gill slits in sharks and used for lift and control of movement. Also called flippers in cetaceans In rays enlarged pectoral fins are attached to the back of the skull and united to form a body disc.

pedicellaria: a stalked pincer like structure projecting from the surface of asteroids and echinoids.

pelagic: of, or inhabiting the water column rather than the sea floor; this term is usually applied to free swimming species;
living in open water away from the bottom, organism that drift are plankton, those that swim actively are nekton.

pelvic fins (=ventral fins): paired fins on the underside of the body in sharks and near the tail in rays.

phytoplankton: small plants which drift in open water and carry out photosynthesis, plant plankton, the basis of the aquatic food chain.

plankton: minute plants and animals that live in open water and are primarily transported by currents.

planula (pl. = planulae): a mobile invertebrate larva that is small, flattened and covered by cilia.

polyp: an individual member of a coelenterate colony having a mouth surrounded by a ring of tentacles

radula: a ribbon of replaceable, chitinous teeth that is found only in molluscs.

rhinophore: a protruding tentacle like structure on the head of opisthobranchs, thought to have a sensory function.

rostrum: a projection that extends forward from the head between the eyes.

sessile: permanently attached to the substrate.

siphon: fleshy tube through which water is pumped for respiration and/or feeding but sometimes also for locomotion (e.g. octopus)

species: a group of animals or plants which are capable of mating and producing viable offspring who are themselves capable of reproduction.

spermatophores: packets of sperm found in cephalopods.

spicule: a calcareous or siliceous structure that provides internal support to an animal; small hard structures of diverse shapes providing skeletal support for a variety of invertebrates e.g. sponges, sea-cucumbers, ascidians.

spiracle: an auxiliary respiratory opening behind the eye in sharks and rays through which water can be taken in when the animal is at rest on the bottom or when the mouth is being used for feeding

spongin: a fibrous protein that is use as skeletal material in sponges.

symbiosis: a relationship between two organisms that results in mutual benefit.

taxonomy: the science of classifying all living things by arranging them in groups according to the relationship of each to the others.

tube foot: an external extension of the water vascular system of echinoderms, generally located in a row and terminating in a suction disc.

tubercle: a small wart-shaped projection on the surface of an animal.

tunic: a tough outer covering over the body of ascidians.

ventral: the lower surface or underside of the body or head.

viviparous: giving birth to live young, the embryo develops entirely within the uterus.

water vascular system: a water filled system of tubes that is used for respiration, location and excretion in echinoderms.

zooid: a member of a joined colony e.g. a coral polyp or individual in a colonial ascidian.

zooplankton: small animals that drift in open water including amphipods, copepods, isopods, krill, polychaetes and pterapods.

zooxanthellae: single celled symbiotic algae, often golden brown in colour, that live in the tissues of many hard and soft corals, providing the host with energy from photosynthesis.