33: An Introduction to Animals

Question 1

Animals

Answer 1

A member of a major lineage of eukaryotes (Animalia) whose members typically have a complex, large, multicellular body; eat other organisms; and are mobile. All are heterotrophs. All animals other than sponges have neurons (nerve cells) that transmit electrical signals to other cells and muscle cells that can change the shape of the body by contracting.

Question 2

extracellular matrix (ECM)

Answer 2

A complex meshwork in which animal cells are embedded, consisting of proteins (e.g., collagen, proteoglycan, laminin) and polysaccharides produced by the cells. It includes proteins specialized for cell-cell adhesion and communication.

Question 3

phylum

Answer 3

(plural: phyla) In Linnaeus’ system, a taxonomic category above the class level and below the kingdom level. In plants, sometimes called a division.

Question 4

body plan

Answer 4

The basic architecture of an animal’s body, including the number and arrangement of limbs, body segments, and major tissue layers.

Question 5

sessile

Answer 5

Permanently attached to a substrate; not capable of moving to another location.

Question 6

choanocytes

Answer 6

A specialized, flagellated feeding cell found in choanoflagellates (protists that are the closest living relatives of animals) and sponges (the most ancient animal phylum).

Question 7

colonies

Answer 7

An assemblage of individuals. May refer to an assemblage of semi-independent cells or to a breeding population of multicellular organisms.

Question 8

epithelium

Answer 8

(plural: epithelia) An animal tissue consisting of sheetlike layers of tightly packed cells that line an organ, a gland, a duct, or a body surface. Also called epithelial tissue.

Question 9

spicules

Answer 9

Stiff spike of silica or calcium carbonate that provides structural support in the body of many sponges.

Question 10

tool kit genes

Answer 10

A set of key developmental genes that establishes the body plan of animals and plants present at the origin of the multicellular lineages and elaborated upon over evolutionary time by a process of duplication and divergence. Includes Hox genes.

Question 11

tissues

Answer 11

A group of cells that function as a unit, such as muscle tissue in an animal or xylem tissue in a plant.

Question 12

diploblast

Answer 12

(adjective: diploblastic) An animal whose body develops from two basic embryonic cell layers or tissues – ectoderm and endoderm.

Question 13

triploblast

Answer 13

(adjective: triploblastic) An animal whose body develops from three basic embryonic cell layers or tissues: ectoderm, mesoderm, and endoderm.

Question 14

germ layers

Answer 14

In animals, one of the three basic types of tissue formed during gastrulation; gives rise to all other tissues.

Question 15

ectoderm

Answer 15

The outermost of the three basic cell layers (gem layers) in most animal embryos; gives rise to the outer covering and nervous system.

Question 16

endoderm

Answer 16

The innermost of the three basic cell layers (germ layers) in most animal embryos; gives rise to the digestive tract and organs that connect to it (liver, lungs, etc.).

Question 17

mesoderm

Answer 17

The middle of the three basic cell layers (germ layers) in most animal embryos; gives rise to muscles, bones, blood, and some internal organs (kidney, spleen, etc.).

Question 18

radial symmetry

Answer 18

(“spoke symmetry”) An animal body pattern that has at least two planes of symmetry. Typically, the body is in the form of a cylinder or disk, and the body parts radiate from a central hub.

Question 19

bilateral symmetry

Answer 19

(“two-sided symmetry”) An animal body pattern in which one plane of symmetry divides the body into a left side and a right side. Typically, the body is long and narrow, with a distinct heat end and tail end.

Question 20

bilaterian

Answer 20

A member of a major lineage of animals (Bilateria) that are bilaterally symmetrical at some point in their life cycle, have three embryonic germ layers, and have a coelom. All protostomes and deuterostomes are bilaterians.

Question 21

nerve net

Answer 21

A nervous system in which neurons are diffuse instead of being clustered into large ganglia or traits; found in cnidarians and ctenophores.

Question 22

central nervous system

Answer 22

Large numbers of neurons aggregated into clusters called ganglia in bilateral animals. In vertebrates, the central nervous system consists of the brain and spinal cord.

Question 23

ganglion

Answer 23

(plural: ganglia) A mass of neurons in a centralized nervous system.

Question 24

cephalization

Answer 24

The formation in animals of a distinct anterior region (the head) where sense organs and a mouth are clustered.

Question 25

brain

Answer 25

A large mass of neurons, located in the head region of an animal, that is involved in information processing; may also be called the cerebral ganglion.