ae of UROCHORDATA metamorphosis into adults after settling down at the bottom of the SEA.

Classification:

Kingdom : Animalia

Phylum : Chordata

Subphylum : Urochordata (tunicates)

Class : Ascidacea (sea squirts)

Larvacea (Larvaceans)

Thaliacea(Thaliaceans)

General characteristics of urochordata :

• Urochordata is sometimes known as tunicates and commonly known as sea squirts.

• Marine animals : some species are SOLITARY and others are colonial.

• Body is covered with cuticular tunics or test in adult stage.

• Notochord is present in larval stage and absent in adult stages

• A NUMEROUS gill slits are present.

• Sexes are united , that is HERMAPHRODITE.

• Heart is ventral , simple and tubular.

• Body has more than two cell layers and includes tissues and organs.

• Has no coelomic body cavity.

• Settles head first on hard substrates and undergoes a dramatic metamorphosis (e.g, Tail , notochord , muscle segments and nerve cord disappear)

• Dorsal tubular nerve cord is present in larval forms while degenerates in the form of small GANGLION in adults.