Annelids' cuticles are made of collagen fibers, usually in layers that spiral in alternating directions so that the fibers cross each other. These are secreted by the one-cell deep epidermis (outermost skin layer). A few marine annelids that live in tubes lack cuticles, but their tubes have a similar structure, and mucus-secreting glands in the epidermis protect their skins. Under the epidermis is the dermis, which is made of connective tissue, in other words a combination of cells and non-cellular materials such as collagen. Below this are two layers of muscles, which develop from the lining of the coelom (body cavity): circular muscles make a segment longer and slimmer when they contract, while under them are longitudinal muscles, usually four distinct strips, whose contractions make the segment shorter and fatter. Some annelids also have oblique internal muscles that connect the underside of the body to each side. COUNT 5
QSN1 How are the layers arranged in annelids' cuticles? ANS1 spiral in alternating directions QSN2 What are annelids' cuticles made out of? ANS2 collagen fibers QSN3 What do non-cuticle annelids use to protect their skin? ANS3 mucus-secreting glands in the epidermis QSN4 What layer is under the epidermis? ANS4 the dermis QSN5 What does 'coelom' mean? ANS5 (body cavity