Ch. 27 Key Terms - Biology 2e

Key vocabulary terms from Chapter 27 of Biology 2e covering animal development, symmetry, and geological evolutionary periods.

acoelomate

animal without a body cavity

bilateral symmetry

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

blastopore

opening into the archenteron that forms during gastrulation

blastula

$16$-$32$ cell stage of development of an animal embryo

body plan

morphology or defining shape of an organism

Cambrian explosion

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

cleavage

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

coelom

lined body cavity

Cryogenian period

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

determinate cleavage

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

deuterostome

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

diploblast

animal that develops from two germ layers

Ecdysozoa

clade of protostomes that exhibit exoskeletal molting (ecdysis)

Ediacaran period

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

enterocoely

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

eucoelomate

animal with a body cavity completely lined with mesodermal tissue

Eumetazoa

group of animals with true differentiated tissues

gastrula

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

germ layer

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

Hox gene (also, homeobox gene)

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

indeterminate cleavage

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

Lophotrochozoa

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

mass extinction

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

Metazoa

group containing all animals

organogenesis

formation of organs in animal embryogenesis

Parazoa

group of animals without true differentiated tissues

protostome

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

pseudocoelomate

animal with a body cavity located between the mesoderm and endoderm

radial cleavage

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

radial symmetry

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

schizocoely

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

spiral cleavage

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

triploblast

animal that develops from three germ layers

Acanthostega

one of the earliest known tetrapods

Actinopterygii

ray-finned fishes

allantois

membrane of the egg that stores nitrogenous wastes produced by the embryo; also facilitates respiration

amnion

membrane of the egg that protects the embryo from mechanical shock and prevents dehydration

amniote

animal that produces a terrestrially adapted egg protected by amniotic membranes

Amphibia

frogs, salamanders, and caecilians

ampulla of Lorenzini

sensory organ that allows sharks to detect electromagnetic fields produced by living things

anapsid

animal having no temporal fenestrae in the cranium

anthropoid

monkeys, apes, and humans

Anura

frogs

apocrine gland

scent gland that secretes substances that are used for chemical communication

Apoda

caecilians

Archaeopteryx

transition species from dinosaur to bird from the Jurassic period

archosaur

modern crocodilian or bird, or an extinct pterosaur or dinosaur

Australopithecus

genus of hominins that evolved in eastern Africa approximately four million years ago

brachiation

movement through trees branches via suspension from the arms

brumation

period of much reduced metabolism and torpor that occurs in any ectotherm in cold weather

caecilian

legless amphibian that belongs to the clade Apoda

Casineria

one of the oldest known amniotes; had both amphibian and reptilian characteristics

Catarrhini

clade of Old World monkeys

Cephalochordata

chordate clade whose members possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage

Chondrichthyes

jawed fish with paired fins and a skeleton made of cartilage

Chordata

phylum of animals distinguished by their possession of a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some point during their development

chorion

membrane of the egg that surrounds the embryo and yolk sac

contour feather

feather that creates an aerodynamic surface for efficient flight

Craniata

clade composed of chordates that possess a cranium; includes Vertebrata together with hagfishes

cranium

bony, cartilaginous, or fibrous structure surrounding the brain, jaw, and facial bones

Crocodilia

crocodiles and alligators

cutaneous respiration

gas exchange through the skin

dentary

single bone that comprises the lower jaw of mammals

diapsid

animal having two temporal fenestrae in the cranium

diphyodont

refers to the possession of two sets of teeth in a lifetime

dorsal hollow nerve cord

hollow, tubular structure derived from ectoderm, which is located dorsal to the notochord in chordates

down feather

feather specialized for insulation

eccrine gland

sweat gland

Enantiornithes

dominant bird group during the Cretaceous period

eutherian mammal

mammal that possesses a complex placenta, which connects a fetus to the mother; sometimes called placental mammals

flight feather

feather specialized for flight

frog

tail-less amphibian that belongs to the clade Anura

furcula

wishbone formed by the fusing of the clavicles

gnathostome

jawed fish

Gorilla

genus of gorillas

hagfish

eel-like jawless fish that live on the ocean floor and are scavengers

heterodont tooth

different types of teeth that are modified for different purposes

hominin

species that are more closely related to humans than chimpanzees

hominoid

pertaining to great apes and humans

Homo

genus of humans

Homo sapiens sapiens

anatomically modern humans

Hylobatidae

family of gibbons

Hylonomus

one of the earliest reptiles

lamprey

jawless fish characterized by a toothed, funnel-like, sucking mouth

lancelet

member of Cephalochordata; named for its blade-like shape

lateral line

sense organ that runs the length of a fish’s body; used to detect vibration in the water

lepidosaur

modern lizards, snakes, and tuataras

mammal

one of the groups of endothermic vertebrates that possesses hair and mammary glands

mammary gland

in female mammals, a gland that produces milk for newborns

marsupial

one of the groups of mammals that includes the kangaroo, koala, bandicoot, Tasmanian devil, and several other species; young develop within a pouch

monotreme

egg-laying mammal

Myxini

hagfishes

Neognathae

birds other than the Paleognathae

Neornithes

modern birds

notochord

flexible, rod-shaped support structure that is found in the embryonic stage of all chordates and in the adult stage of some chordates

Ornithorhynchidae

clade that includes the duck-billed platypus

Osteichthyes

bony fish

ostracoderm

one of the earliest jawless fish covered in bone

Paleognathae

ratites; flightless birds, including ostriches and emus

Pan

genus of chimpanzees and bonobos