Characteristics of Chordates

Chordates are deuterostomes (like the echinoderms). Are you surprised to find out you're closely related to a starfish?

Every animal is a combination of traits. Some traits are conserved from remote ancestors. Other traits are unique to its branch of the family tree.

The phylum Chordata consists of a majority of species that are vertebrates (with a back-bone) and a minority that are invertebrate chordates. All chordates, at some time in their lives, have four distinctive features:

A notochord which is a long rod of stiffened tissue that supports the body. Later in development, it changes to bony units in vertebrates.
A dorsal, tubular nerve cord lies above the notochord and gut.
A muscular pharynx with gill slits is positioned at the entrance to the digestive tract (at least in the embryo).
A tail, or rudiment thereof, exists near the anus (at least in the embryo).

The phylum chordata has three subphyla:

Urochordata (tunicates),
Cephalochordata (lancelets), and
Vertebrata (vertebrates).

This animation (Audio - Important) describes the evolution of chordates.

Urochordata and Cephalochordata and called the invertebrate subphyla. The Vertebrata have a backbone of cartilage or bone and a brain encased in a protective skull.

The vertebrates are divided into eight classes (one of which is extinct).

Agnatha - jawless fishes
Placodermi - jawed armored fishes (extinct)
Chondrichthyes - cartilaginous fishes
Osteichthyes - bony fishes
Amphibia - Amphibians
Reptilia - Reptiles
Aves - Birds
Mammalia - Mammals

REVIEW: Only _____ have a notochord, a tubular dorsal nerve cord, a pharynx with slits in the walls, and a tail extending past the anus.
a. echinoderms
b. tunicates and lancelets
c. vertebrates
d. both b and c
e. all of the above