Biology Chapter 34 Vocabulary

Chordates

Members of the phylum Chordata, animals that at some point during their development have a notochord; a dorsal, hollow nerve cord; pharyngeal slits or clefts; and a muscular, post-anal tail.

notochord

A longitudinal, flexible rod made of tightly packed mesodermal cells that runs along the anterior-posterior axis of a chordate in the dorsal part of the body.

pharyngeal clefts

In chordate embryos, the grooves that separate a series of arches along the outer surface of the pharynx and may develop into a pharyngeal slit.

pharyngeal slits

In chordate embryos, the narrow openings that form from the pharyngeal clefts and open into the pharynx, later developing into gill slits in many vertebrates.

lancelets

Members of the clade Cephalochordata, small blade-shaped marine chordates that lack a backbone.

tunicates

Members of the clade Urochordata, sessile marine chordates that lack a backbone.

neural crest

In vertebrates, a region located along the sides of the neural tube where it pinches off from the ectoderm. Neural crest cells migrate to various parts of the embryo and form pigment cells in the skin and parts of the skull, teeth, adrenal glands, and peripheral nervous system.

hagfishes

Marine jawless vertebrates that have highly reduced vertebrae and a skull made of cartilage; most hagfishes are bottom-dwelling scavengers.

lampreys

Jawless vertebrates with highly reduced vertebrae that live in freshwater and marine environments. Almost half of extant lamprey species are parasites that feed by clamping their round, jawless mouth onto the flank of a live fish; nonparasitic lampreys are suspension feeders that feed only as larvae.

cyclostomes

Members of one of the two main clades of vertebrates; cyclostomes lack jaws and include lampreys and hagfishes.

conodonts

Early, soft-bodied vertebrates with prominent eyes and dental elements.

gnathostomes

Members of one of the two main clades of vertebrates; gnathostomes have jaws and include sharks and rays, ray-finned fishes, coelacanths, lungfishes, amphibians, reptiles, and mammals.

lateral line system

A mechanoreceptor system consisting of a series of pores and receptor units along the sides of the body in fishes and aquatic amphibians; detects water movements made by the animal itself and by other moving objects.

placoderms

Members of an extinct group of fishlike vertebrates that had jaws and were enclosed in a tough outer armor.

acanthodians

A group of ancient jawed aquatic vertebrates from the Silurian and Devonian periods.

chondrichthyans

Members of the clade Chondrichthyes, vertebrates with skeletons made mostly of cartilage, such as sharks and rays.

oviparous

Referring to a type of development in which young hatch from eggs laid outside the female’s body.

ovoviviparous

Referring to a type of development in which young hatch from eggs that are retained in the uterus.

viviparous

Referring to a type of development in which the young are born alive after having been nourished in the uterus by blood from the placenta.

cloaca

A common opening for the digestive, urinary, and reproductive tracts found in many nonmammalian vertebrates but in few mammals

osteichthyans

A member of a vertebrate clade with jaws and mostly bony skeletons.

operculum

In aquatic osteichthyans, a protective bony flap that covers and protects the gills.

swim bladder

In aquatic osteichthyans, an air sac that enables the animal to control its buoyancy in the water.

ray-finned fishes

Members of the clade Actinopterygii, aquatic osteichthyans with fins supported by long, flexible rays, including tuna, bass, and herring.

lobe-fins

Members of a clade of osteichthyans having rod-shaped muscular fins. The group includes coelacanths, lungfishes, and tetrapods.

tetrapods

A vertebrate clade whose members have limbs with digits. Tetrapods include mammals, amphibians, and birds and other reptiles.

amphibians

The clade of tetrapods that includes salamanders, frogs, and caecilians.

amniotes

A clade of tetrapods named for a key derived character, the amniotic egg, which contains specialized membranes, including the fluid-filled amnion, that protect the embryo. Amniotes include mammals as well as birds and other reptiles.

amniotic egg

An egg that contains specialized membranes that function in protection, nourishment, and gas exchange. The amniotic egg was a major evolutionary innovation, allowing embryos to develop on land in a fluid-filled sac, thus reducing the dependence of tetrapods on water for reproduction.

reptile

A member of the clade of amniotes that includes tuataras, lizards and snakes, turtles, crocodilians, and birds.

ectothermic

Referring to organisms for which external sources provide most of the heat for temperature regulation.

endothermic

Referring to organisms that are warmed by heat generated by their own metabolism. This heat usually maintains a relatively stable body temperature higher than that of the external environment.

diapsids

Members of an amniote clade distinguished by having a pair of holes on each side of the skull. Diapsids include the lepidosaurs and archosaurs.

lepidosaurs

Members of the reptilian group that includes lizards, snakes, and two species of New Zealand animals called tuataras.

archosaurs

The reptilian group that includes crocodiles, alligators and dinosaurs, including birds.

Pterosaurs

Winged reptiles that lived during the Mesozoic era.

dinosaurs

Members of an extremely diverse clade of reptiles varying in body shape, size, and habitat. Birds are the only extant dinosaurs.

ratites

Members of the group of flightless birds.

mammals

Members of the clade Mammalia, amniotes that have hair and mammary glands (glands that produce milk).

synapsids

Members of an amniote clade distinguished by having a single hole on each side of the skull. Synapsids include the mammals.

Monotremes

Egg-laying mammals, such as the platypus or echidna. Like all mammals, monotremes have hair and produce milk, but they lack nipples.

marsupials

Mammals, such as a koalas, kangaroos, or opossums, whose young complete their embryonic development inside a maternal pouch called the marsupium.

placenta

A structure in the uterus of a pregnant eutherian mammal that nourishes the fetus with the maternal blood supply; formed from the uterine lining and embryonic membranes.

Eutherians

Placental mammals; mammals whose young complete their embryonic development within the uterus, joined to the female parent by the placenta.

opposable thumb

A thumb that can touch the ventral surface (fingerprint side) of the fingertip of all four fingers of the same hand with its own ventral surface.

anthropoids

Members of a primate group made up of the monkeys and the apes (gibbons, orangutans, gorillas, chimpanzees, bonobos, and humans).

paleoanthropology

The study of human origins and evolution

hominins

A group consisting of humans and the extinct species that are more closely related to humans than to chimpanzees.