Xyloplax janetae is a flattened disk, from in diameter, and about thick. It has adambulacral spines which are spines that project radially from the margin of the animal, of distinctmorphology. On its dorsal it has many projecting abactinal spines whose morphology is distinct from the adambulacral spines.
Xyloplax janetae is a bathyal abyssal species, meaning it is found in the deepest part of the open ocean. It has only been found clinging to sunken wood.