Most members of Phylum Chordata are vertebrates (animals with backbones), however two sub-phyla are invertebrates (having no backbone). These are sub-phyla Urochordata and Cephalochordata.
Subphylum Urochordata:
These animals include the sea squirt or tunicate. The name sea squirt refers to its method of defense: when it is disturbed it shoots a stream of water out of its excurrent siphon at its attacker. Only in the tadpole larva stage to they possess a notochord, nerve cord, gill slits, and a tail. During development it attaches to a hard surface and undergoes metamorphosis, during which the notochord, nerve cord, and tail disappear. It retains only the gill slits as an adult. Tunicate refers to the leathery tunic that surrounds the adult called a house. Tunicate larvae have no house because it would limit mobility. It filter feeds by filtering water through its gill slits. Water and wastes leave the body through an excurrent siphon.
Basic Facts:
1. There are approximately 2000 species identified.
2. All are marine animals.
3. Most common is the sea squirt
4. Eat by filter feeding.
5. Are sessile or stationary as adults.
6. Either live in colonies or as individuals(alone). Subphylum Cephalochordata
Cephalochordates are "fish-like" invertebrates of the chordate subphylum Cephalochordata. Typtical is the lancelet, which has all four chordate characteristics as adults. The notochord never develops into a backbone. They can swim but spend most of their time burried in the sand with their heads exposed. In this fashion they filter feed through their gill slits. The muscles of a lancet are arranged along the body in a V-shaped segments which enables muscle bundles to pull independently against the notochord resulting in smooth side-to-side movements.
Basic Facts:
1. About 200 species of Cephalochordatea have been identified.
2. Live in shallow water along sea coasts.
3. Cephalochordate means "chordate with a head."
4. Has a head, sensory organs, undergoes respiration, and filter feeds.
5. Most typtical is the amphioxus (am-fee-ox-us).
6. Has segmented muscles. Subphylum Vertebrata
Vertebrates, members of Subphylum Vertebrata of Phylum Chordata, all share four main characteristrics. These are a dorsal nerve cord, a notochord, gill slits(or pouches), and a post-anal tail. In most vertebrates the dorsal nerve cord develops into a brain and spinal cord, while the notochord develops into a "bony" backbone. In general, gill slits become gills in aquatic vertebrates and lungs in land vertebrates. The post-anal tail is the only characteristic retained in most adult vertebrates.
Basic Facts:
1. Approximately 40,000 species exist.
2. Have an internal framework called the endoskeletonthat may be made of cartilage or bone or both.
3. All skeletons are built on a similar plan:
a) a skull
b) a rib cage
c) a vertebral column or backbone made of bony segments called vertebrae.
d) the skull, vertebral column, and rib cage make up the axil skeleton.
4. Most vertebrates have two pairs of limbs, attached to the axil skeleton by bones called the pectoral girdle and pelvic girdle respectively.
5. The limb bones (arms, legs, wings, etc) and the two girdles make up the appendicular skeleton.
