Psolidium

Ludwig, 1887

29 species

Small forms, sole sharply set off with feet along the edges and a few or many in the mid-ventral ambulacrum. Dorsal side with numerous imbricating scales, and a varying number of tube feet which pass through some of the scales. Spicules in sole plates or buttons smooth to knobbed, usually also an external layer of deep small cups. Feet end plate and supporting plates or rods. Dorsal side usually with an external layer of cups (possibly lacking in some species) besides grain or towers (more or less completely reduced with age). Dorsal tube feet without end plate and supporting rods or plates in the walls. (Deichmann, 1930)