THE STRUCTURE OF BODY WALL AND ENDOSKEHON OF STAR FISH.
The body wall of star firsh consists of 1. Epidermis 2. Dermis 3. Muscles and 4. Coelomic epithelium.
1. Epidermis : The epidermis is made by ciliated columnar epithelium. It secretes a thin layer of cuticle. The cuticle and epidermis will cover the tube feet, pedicellariae and dermal branchiae. Neuro-sensory cells are scattered here and there in the epidermis. They are spindle shaped. These cells are connected with network of nerve fibres present below the epidermis. Club shaped gland cells are also scattered here and there in the epidermis. They secrete mucous. It forms a protective layer on the body.
2. Dermis: The dermis is formed of fibrous connective tissue. It is formed from the mesoderm. It is very thick and divisible into outer and inner regions. The outer region secretes ossicles. They form the endoskeleton. The inner region of the dermis contains perihaemal spaces.
3. Muscles : They are smooth muscles. They are outer circular and an inner longitudinal muscles.
4. Coelomic Epitbelim : The coelomic epithelium is made by cubical cells. They are ciliated. It is called parietal peritoneum.
Functions of body wall -.
1. It gives protection to the internal organs.
2. It produces endoskeleton.
3. The cilia and pedicellariae clean the surface and dermabranchiae.
4. The peritoneum secretes coelomic fluied.
Endoskeleton s The endoskeleton is made by calcareous ossicles. They are secretd by dermis. Each ossicle is made by a network of calcareous rods. The
ossicles are connected by connective tissue and muscles. Ossicles are irregularly arranged on the aboral side. They lie in two rows on either side of the ambulacral groove. These ossicles are long. They are called the ambulacral ossicles. The ossicles show notches, two near by ossicles will show a round opening, through this opening tube feet will come out.