Orbit-worms

The orbit-worms (Family Orbiniidae) are active burrowers, although they apparently do not feed while they excavate. The cylindrical, ragged appearance of their mid- to posterior ends is distinctive. The “raggedness” is a result of the increase in size of the paired, lateral branchiae (gills) that almost touch each other across the dorsal (upper) surface. As well, a transition of the parapodia (paired fleshy appendages) from a lateral orientation to a more dorsal position, produces a circular, almost tubular shape to the body in cross-section. About half of the orbit-worm species spawn freely into the seawater and the rest deposit their eggs into gelatinous (sometimes ribbon-shaped) masses or cocoons. For intertidal species, these cocoons apparently provide better protection for the eggs from predators, desiccation and salinity fluctuations.