BRANCHIOSTOMA-SKELETON

has no skeleton. A number of endoskeletal structures are present. They are neither bony nor cartilagnious.

BRANCHIOSTOMA-MUSCULATURE

The muscles lying beneath the skin form the part of body wall. They are thick in dorso-lateral regions.They length of body present ina series of v-shaped myotomes or myomeres. The pointed apex of the vis anteriorly. In B.lanceolatum 60-62 myotomes are present. Myotomes are enveloped in a thin connective tissue layer . Due to their peculiar arragement several myotomes and myocommata . The myotomes help in lateral undulating movements of body as they can be twisted .Their contractions help in driving water of atrival cavity out of the atriopore.

BRANCHIOSTOMA-PERITONEUM

The muscle layer is lined internally by a thin layer of parietal paritoneum. It is not continuous in the pharyngeal region .

BRANCHIOSTOMA-MYOTOMES

The lateral side of body a series of muscle bands,called myotomes or myomeres. Between mouth and atriopore present on either side below the myotomes gonads.

BRANCHIOSTOMA-BODY WALL

The body wall includes from outside- A thin delicate and transparent skin .
A well-developed musculature.
A parietal peritoneum.

BRANCHIOSTOMA-MYOTOMES AND GONADS

On each lateral side of body a series of v-shaped muscle band called myotomes or myomeres  present. Between mouth and atriopore, present on eitherside below the myotomes .A series of gonads also present..

BRANCHIOSTOMA-FINS AND FOLDS

Branchiostoma bears three fins dorsal, caudal and ventral. The dorsal fins runs as a low, mid-dorsal fold along the entire length of trunk. It is contianuous behind with a much broader caudal fin around the tail. The ventral fin runs mid-ventrally from caudal fin upto atriopore. It is slightly wider than the dorsal fin. Fin rays are lacking in the caudal fin.The structure of fins and fin-ray boxes is different from that in fishes. Paired fins are absent.The are two hollow membranous metapleural folds.The two folds are connected by a horizontal fold of body wall, called epipleur, which forms the floor of the body.