sessile

describes an organism that lives and grows while attached to something else (nonmotile)

endoskeleton

an internal skeleton usually made of bone and cartilage; a characteristic of vertebrate animals

exoskeleton

a system of stiff external plates for support and protection; a characteristic of many invertebrate animals

hydroskeleton

a support structure in many soft-bodied animals consisting of a fluid-filled cavity surrounded by muscles

body plan

the arrangement of physical features in an organism that contributes to its structure and form

bilateral symmetry

a type of symmetry in animals in which an imaginary plane through the centerline of the organism divides it into mirror-image halves

radial symmetry

a type of symmetry in animals that do not have left and right halves. Mirror-image halves can be produced by several imaginary planes through the center of the body

vertebrate

an animal that has a backbone or vertebral column

chordate

an organism in phylum Chordata

invertebrate

an animal that does not have a backbone or vertebral column

endotherm

an animal whose body temperature is internally regulated and whose body heat is derived mainly from metabolism

ectotherm

an animal whose body temperature remains close to the temperature of its environment

blastula

an early stage of embryonic development consisting of a hollow, fluid-filled ball of cells

germ layer

one of two or three primary layers of cells that form early in embryonic development

endoderm

the inner germ layer of an embryo

mesoderm

the middle germ layer of an embryo

ectoderm

the outer germ layer of an embryo

cephalization

the concentration of sensory organs around one end of an organism, usually the head

anus

the opening at the end of the alimentary canal through which solid waste is eliminated

external fertilization

the uniting of sperm and egg cells outside an organism's body

internal fertilization

the uniting of sperm and egg cells inside the body of a female organism

oviparous species

an organism that uses a method of reproduction in which young develop inside eggs that are laid and hatched outside the parent's body

viviparous species

an organism that uses a method of reproduction in which young are born alive after developing inside the female's reproductive tract

ovoviviparous species

an organism that uses a method of reproduction in which young develop within eggs that hatch inside the parent's body

behavior

the way that an animal responds to its environment

instinct

a built-in response to the environment