Physical characteristics

Body length varies from several millimeters to more than 18 in (45 cm) and corresponds to the extended size, which is generally approximately five times longer than the contracted size. Body diameter varies from 0.006 in (0.15 mm) to approximately 0.2 in (5 mm). Color is generally fleshy, sometimes brownish to black.

The other features are anatomical. Phoronids have at least two body regions in larval and adult forms, each containing its own coelom. A lophophore, defined as a tentacular extension of the mesosome (and of its coelomic cavity, the mesocoelom) embraces the mouth but not the anus. The main functions of the lophophore are feeding, respiration, and protection. The site and shape of the lophophore are proportional to body size, ranging from oval to horseshoe to helicoidal in relation to an increase in the number of tentacles. Phoronids have a U-shaped digestive tract. A nervous center is present between the mouth and anus, as is a ring nerve at the base of the lophophore, and the animal has one or two giant nerve fibers. Phoronids have one pair of nephridia and a closed circulatory system with red blood corpuscles.

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