12.1 vertebrates

Vocabulary terms and definitions focusing on chordate evolution, the five major chordate characteristics, and the biological features of SubPhylum Urochordata.

Chordate evolution

A history of innovations that is built upon major invertebrate traits such as bilateral symmetry, cephalization, segmentation, and a coelom or "gut" tube.

Adaptive radiations

The development of a variety of forms from a single ancestral group.

Natural Selection

The process by which structures, such as the forelimb of mammals, are specialized to produce a wide range of structural variation.

Notochord

A stiff, flexible rod that provides internal support; it remains throughout the life of most invertebrate chordates but occurs only in the embryos of vertebrate chordates.

Dorsal Hollow Nerve Chord (Spinal cord)

A fluid-filled tube of nerve tissue that runs the length of the animal, present in chordates just dorsal to the notochord throughout embryonic and adult life.

Pharyngeal gill slits

Pairs of opening through the pharynx used to filter food in invertebrate chordates, which develop into true gills in fishes and are vestiges in reptiles, birds, and mammals.

Postanal Tail

A structure that provides motility and stability, working with muscles and the notochord for propulsion; it is vestigial later in some lineages.

Myomeres

Muscle segments that work with the postanal tail and notochord to provide motility.

Endostyle

A mucous secreting structure found in the pharynx floor that traps small food particles.

SubPhylum Urochordata

A group of invertebrate chordates, such as tunicates or sea squirts, that are sessile as adults but motile during larval stages.

Urochordate Larvae

The motile stage of SubPhylum Urochordata that possesses all $5$ chordate characteristics (tail, notochord, muscle segments, and nerve chord).

Urochordate Metamorphosis

A dramatic change where larvae settle head first on hard substrates and the tail, notochord, muscle segments, and nerve chord disappear.

Tunic

An outer envelope that covers the adult body of a tunicate (Urochordata).

Tunicates

Filter feeders whose body encloses a basket-like pharynx perforated by gill slits, where plankton is trapped in a sheet of mucus.

Excurrent siphon

The structure through which water leaves the body of a tunicate.