ch. 27

Question 1

acoelomate

Answer 1

animal without a body cavity

Question 2

bilateral symmetry

Answer 2

type of symmetry in which there is only one plane of symmetry, so the left and right halves of an animal are mirror images

Question 3

blastopore

Answer 3

opening into the archenteron that forms during gastrulation

Question 4

blastula

Answer 4

16–32 cell stage of development of an animal embryo

Question 5

body plan

Answer 5

morphology or defining shape of an organism

Question 6

Cambrian explosion

Answer 6

time during the Cambrian period (542–488 million years ago) when most of the animal phyla in existence today evolved

Question 7

cleavage

Answer 7

cell divisions subdividing a fertilized egg (zygote) to form a multicellular embryo

Question 8

coelom

Answer 8

lined body cavity

Question 9

Cryogenian period

Answer 9

geologic period (850–630 million years ago) characterized by a very cold global climate

Question 10

determinate cleavage

Answer 10

cleavage pattern in which developmental fate of each blastomere is tightly defined

Question 11

deuterostome

Answer 11

blastopore develops into the anus, with the second opening developing into the mouth

Question 12

diploblast

Answer 12

animal that develops from two germ layers

Question 13

Ecdysozoa

Answer 13

clade of protostomes that exhibit exoskeletal molting (ecdysis)

Question 14

Ediacaran period

Answer 14

geological period (630–542 million years ago) when the oldest definite multicellular organisms with tissues evolved

Question 15

enterocoely

Answer 15

mesoderm of deuterostomes develops as pouches that are pinched off from endodermal tissue, cavity contained within the pouches becomes coelom

Question 16

eucoelomate

Answer 16

animal with a body cavity completely lined with mesodermal tissue

Question 17

Eumetazoa

Answer 17

group of animals with true differentiated tissues

Question 18

gastrula

Answer 18

stage of animal development characterized by the formation of the digestive cavity

Question 19

germ layer

Answer 19

collection of cells formed during embryogenesis that will give rise to future body tissues, more pronounced in vertebrate embryogenesis

Question 20

Hox gene

Answer 20

master control gene that can turn on or off large numbers of other genes during embryogenesis

Question 21

indeterminate cleavage

Answer 21

cleavage pattern in which individual blastomeres have the character of “stem cells,” and are not yet predetermined to develop into specific cell types

Question 22

Lophotrochozoa

Answer 22

clade of protostomes that exhibit a trochophore larvae stage or a lophophore feeding structure

Question 23

mass extinction

Answer 23

event or environmental condition that wipes out the majority of species within a relatively short geological time period

Question 24

Metazoa

Answer 24

group containing all animals

Question 25

organogenesis

Answer 25

formation of organs in animal embryogenesis

Question 26

Parazoa

Answer 26

group of animals without true differentiated tissues

Question 27

protostome

Answer 27

blastopore develops into the mouth of protostomes, with the second opening developing into the anus

Question 28

pseudocoelomate

Answer 28

animal with a body cavity located between the mesoderm and endoderm

Question 29

radial cleavage

Answer 29

cleavage axes are parallel or perpendicular to the polar axis, resulting in the alignment of cells between the two poles

Question 30

radial symmetry

Answer 30

type of symmetry with multiple planes of symmetry, with body parts (rays) arranged around a central disk

Question 31

schizocoely

Answer 31

during development of protostomes, a solid mass of mesoderm splits apart and forms the hollow opening of the coelom

Question 32

spiral cleavage

Answer 32

cells of one pole of the embryo are rotated or misaligned with respect to the cells of the opposite pole

Question 33

triploblast

Answer 33

animal that develops from three germ layers