Chapter 32: The Deuterostomes

Frog embryos

develop into tadpoles, which undergo metamorphosis to become adults.

hagfishes

The , which make up the Myxini, and the lampreys, which make up.

Biologists

classify amniotes in two main groups: diapsids and synapsids.

Jaws

and paired fins are absent in both hagfishes and lampreys.

Tiktaalik

was a transitional form between fishes and tetrapods.

Hemichordates

(acorn worms) are marine deuterostomes with a three- part body, including proboscis, collar, and trunk.

Echinoids

lack arms; they have a solid shell and are covered with spines.

Mammals

have hair, mammary glands, differentiated teeth, lungs with alveoli, completely divided ventricles, and three middle- ear bones.

Eutherians

are more developed at birth than marsupials; they are characterized by a well- developed placenta, an organ of exchange that develops between the embryo and the mother.

Synapsids

The include the therapsids, which gave rise to the mammals.

Class Holothuroidea

consists of sea cucumbers, animals with elongated flexible bodies.

Amphibians

use their moist skin as well as lungs for gas exchange.

Class Asteroidea

consists of the sea stars.

Birds

have many adaptations for powered flight, including feathers; wings; and light, hollow bones containing air spaces.

Vertebrates

have pronounced cephalization, a complex brain, a muscular pharynx, and muscles attached to the endoskeleton.

Class Ophiuroidea

includes the brittle stars, which resemble sea stars but have longer, more slender arms that are set off more distinctly from the central disc.

Lancelets

The are cephalochordates, small, segmented, fishlike animals; their chordate characteristics are highly developed.

Petromyzontida

The , have neither jaws nor paired fins.

Monotremes

lay eggs.

oral surface of crinoids

The is turned upward; some crinoids are sessile.

Neural crest cells

are embryonic cells important in the development of many structures, including the cranium and jaws.

central disc

They have a(n) with five or more arms, and they use tube feet for locomotion.

Chondrichthyes

The comprise the sharks, rays, and skates; they are jawed fishes with skeletons of cartilage.

Hagfishes

are marine scavengers that secrete slime as a defense mechanism.

jaws

They have , two pairs of fins, and placoid scales.

Vertebrates

can be assigned to nine classes.

Shared derived characters include

radial, indeterminate cleavage; the blastopore becomes (or is near the future site of) the anus; and pharyngeal slits at some time in the life cycle

The chordates (Phylum Chordata) include three subphyla

Urochordata, Cephalochordata, and Vertebrata

The extant (living) bony fishes can be assigned to three classes

Actinopterygii, ray finned fishes; Actinistia, coelacanths; and Dipnoi, lungfishes

During the Devonian period, bony fishes gave rise to two evolutionary lines

th Actinopterygii, or ray-finned fishes, and the Sarcopterygii, or lobe-finned fishes

Biologists classify amniotes in two main groups

diapsids and synapsids