A
ampullae of Lorenzini
Skin pores containing receptor cells sensitive to electric fields

B

C
caudal fin
The tail fin.
chemoreceptors
Cells or organs sensitive to chemical stimulation.
chondrichthyes
Fishes that have a skeleton made out of cartilage (sharks, rays, chimaeras).
chondrocyte
Cartilage cell
claspers
A posterior extension on each of the pelvic fins of male sharks that aids in the transmission of sperm during copulation.
cloaca
The common cavity into which the intestinal, genital, and urinary tracts open in vertebrates such as fish, reptiles, birds, and some primitive mammals.
crustaceans
An animal class among the arthropods including lobsters, crabs, shrimps, etc.

D
denticles
Synonymous to placoid scales.

E
ectotherm
An organism that regulates its body temperature largely by exchanging heat with its surroundings.
embryo
The developing young before birth or hatching.
enamel
The hard, calcareous substance covering the exposed portion of a tooth.
endolymphatic ducts
Duct connecting the membranous labyrinth of the ear with the world around.
epidermis
The outer, protective, nonvascular layer of the skin of vertebrates.
estuaries
The part of the wide lower course of a river where its current is met by the tides.
external fertilization
The female ejects the eggs and they are fertilized outside the body by males.

F

G
gestation
The period of development in the uterus from fertilization until birth; pregnancy.
guanine
Light pigment responsible for the reflecting surface of the tapetum lucidum (also the silvery or white appearance of bony fishes).

H
habitat
The area or environment where an organism or ecological community normally lives or occurs.

I
internal fertilization
The female keeps the eggs inside her body where the male fertilizes them, often with the help of copulation organs.
invertebrate
Lacking a backbone or spinal column; not vertebrate.

J

K

L

M
melanin
A group of naturally occurring dark pigments, found in skin, hair, fur, feathers, etc.
mollusk
Marine invertebrates of the phylum Mollusca (cuttlefish, octopus, mussel, clam, snail...).

N
niche
The function or position of an organism or population within an ecological community.

O
olfactory sacs
Part of the olfactory organs (organ for smelling) situated in the front part of the head and lined with epithelium innervated by the olfactory nerves.
operculum
A lid or flap covering an opening.
osteichthyes
Fishes that have a skeleton composed of bone in addition to cartilage.
osteocyte
Bone cell
ostium
Passage between the ovary and the shell gland.
ovary
The usually paired female reproductive organ that produces eggs.
oviparous
Producing eggs that hatch outside the body.
ovophagy
Synonymous to uterine cannibalism.
ovoviviparous
Producing eggs that hatch within the female's body without obtaining nourishment from it.

P
pelvic fins
The pair of fins on the undersurface of the shark body behind the pectoral fins and lying to either side of the external opening of the cloaca.
placenta
An organ that develops in female mammals (and some sharks) during pregnancy, lining the uterine wall and attached to the embryo.
placoid scales
The hard toothlike scales of sharks, skates, and rays.
plankton
The collection of small or microscopic organisms, including algae and protozoans, that float or drift in great numbers in fresh or salt water, especially at or near the surface.
pulp
The soft tissue forming the inner structure of a tooth and containing nerves and blood vessels.

Q

R
retina
A multilayered, light-sensitive membrane lining the inner eyeball and connected by the optic nerve to the brain.

S
sacculus
The smaller of two membranous sacs in the vestibule of the inner ear.
spiracle
A small respiratory opening behind the eye of certain fishes, such as sharks, rays, and skates.

T
tapetum lucidum
An area in the pigmented layer of the eye in many animals, which has an iridescent or metallic luster and helps to make the eye visible in the dark.
testis
The reproductive gland in a male vertebrate; testicles.

U
uterine cannibalism
When the embryo feeds on its unborn siblings, unfertelized eggs as well as unborn embryos.
uterus
A hollow muscular organ located in the pelvic cavity of female mammals in which the fertilized egg implants and develops. Also called womb.
utriculus
A part of the membranous labyrinth of the ear.

V
vertebrae
Any of the bones or cartilaginous segments forming the spinal column.
vertebrate
Animals that have a backbone or spinal column.
viviparous
Giving birth to living offspring that develop within the mother's body.

W

X

Y
yolk sac
A membranous sac attached to an embryo, providing early nourishment.

Z