Asteria Rubens- Starfish
The body wall consists of a thin, outer epidermis, a thick dermis formed of connective tissue, and a thin, inner peritoneum, which contains longitudinal and circular muscles. The dermis contains rather loosely organised ossicles (bony plates). Some bear external granules, tubercles, and spines, sometimes organised in definite patterns and some specialised as pedicellariae. There may also be papulae, thin-walled protrusions of the body cavity that reach through the body wall and extend into the surrounding water, which serve a respiratory function. These structures are supported by collagen fibres set at right angles to each other and arranged in a three-dimensional web with the ossicles and papulae in the interstices. This arrangement enables both easy flexion of the arms by the starfish with the rapid onset of stiffness and rigidity required for actions performed under stress.