This is a small sea cucumber, and although there are reports of specimens 5 cm (2 in) in length, most individuals are considerably less than half that size. The body is usually curved, somewhat swollen at the middle, and slightly tapered at the ends. The thin body wall is very stiff, because of a profusion of skeletal
ossicles. Numerous long, cylindrical tube feet are scattered over the body wall, and there is some tendency for the tube feet to be aligned in rows near the mouth and anus. On the ventral surface of the body they are most numerous, longest, and hairlike. They appear incapable of full retraction, probably because of the dense layer of ossicles in the tube foot wall. In juveniles 0.5 cm (0.25 in) long, the tube feet are in double rows along each radius. Surrounding the anus are five small, radial, calcareous teeth, and two small
papillae are situated above each tooth. The mouth is surrounded by eight long, slender, abundantly branched tentacles and two shorter ventral ones about one-third the length of their neighbors. The body wall ossicles are knobbed buttons with four perforations, two large central knobs, and 9-12 marginal knobs. The tables from the tube feet have slender, curved disks and short, robust spires terminating in several small teeth.
P. belli is dirty white with flecks of brown or maroon. In very small specimens, the flecks are gray and quite dense along the upper surface, especially near the ends of the body. These small individuals appear black to the naked eye. The tips of the tube feet are bordered by a brown ring. The tentacles have yellowish tan stalks and orange side branches with black fronds” (Hendler, Miller, Pawson, Kier 268).
