It is the only family in the monotypic order Aspidosiphonida, which is in the class Phascolosomatidea.

[1][2][3][4][5] The family Aspidosiphonidae is characterized by an oval disk with short tentacles, arranged in a crescent-shape made of an enclosed nuchal organ.

It has a canal of sacs in the coelom, lying in a continuous band.

The anal and caudal shield (at the anterior end) are both made up, not of chitin, but of a horny protein.

It is of note that most, but not all, of the Aspidosiphonidae family has a caudal shield.