Pentamera trachyplaca is a small species that can grow up to 3 cm long. Its body is straight, and only slightly tapered at the ends. It is whitish or flesh coloured. Tube feet are in five crowded bands, with about four rows of tube feet in each band. The tube feet are cylindrical and bristle with ossicles. The bands of tube feet are about equal in width to the intervening space. It has ten darker tentacles, of which the two ventral ones are the smallest.
Skin ossicles: plates with a complex knobbed surface on one side, often built up into a spire; in side view the plate is curved with the knobbed surface on the convex side.
Similar SpeciesPentamera trachyplaca can be confused with: P. populifera, P. lissoplaca, P. pseudocalcigera, Eupentacta quinquesemita and E. pseudoquinquesemita. The Pentamera species are similar externally, so ossicles should be checked to be certain. The Eupentacta species are usually straight rather than V-shaped, and the tube feet give them a spiky look. The external differences among all the above species are subtle, so ossicles should be examined.