ANOXIA - a deficiency of oxygen reaching the tissues of the body of such severity as to result in permanent damage

AQUA-LUNG - a diving device consisting of one or more cylinders of compressed air strapped to the diver's back and sometimes a glass mask placed over the eyes and nose (scuba diving gear).

BARBELS - a slender tactile process on the lips of certain fishes

BLOWHOLE - a hole for breathing, in the top of the head of whales, dolphins and porpoises.

BRADYCARDIA - slow heart action, occurring when cetaceans dive.

BROODING - to sit on (eggs) in order to hatch; incubate

CRUSTACEANS - any of a large class of mostly aquatic arthropods that have a chitinous exoskeleton, a pair of often much modified appendages on each segment and two pairs of antennae (lobsters, shrimps, crabs, wood lice, water fleas and barnacles).

DORSAL - of, on, or near the back.

ECHOLOCATION - a SONAR-like mechanism of orientation in the sensory systems of certain mammals (whales, dolphins, bats, etc.), by which they translate their own echoes into directional signals that permit them to explore their surroundings.

FISH - a cold-blooded vertebrate that lives in water and breathes with gills.

FOSSILS - the hardened remains or traces of an animal or plant of a former age.

GESTATION - the act or period of carrying young in the uterus from conception to birth.

GILLS - a part of the body of a fish designed for breathing under water.

HAREM - a group of females associated with one male - used of polygynous animals.

HIBERNATE - to become inactive or dormant.

INVERTEBRATE - an animal without a backbone.

MELON - the bulbous forehead region in a cetacean composed of fibrous and fatty tissue, which is thought to function as an acoustic lens for focusing sound when the animal is using its echolocation sonar.

OFFSPRING - what is born from a parent; a newborn young.

PARASITE - an organism living in or on another organism at the expense of the host organism.

PATHOGENS - a specific causative agent (as a bacterium or virus) of disease.

PECTORAL - of, in, or on the breast or chest.

PLANKTON - small animal and plant organisms that float or drift in water, such as small crustaceans, algae, etc. This serves as an important source of food for fish.

ROSTRUM - the beak-like part or snout of a cetacean

RUDIMENTARY - very imperfectly developed; of a primitive kind

RUMINATE - to regurgitate and chew again what has been chewed slightly and swallowed before

TERRESTRIAL - living on land

VERTEBRATE - an animal that has a backbone

WEANED - to make a changeover from mother's milk to a regular diet (as in a young mammal)