Aspidosiphonidae is a family of peanut worms. 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. The family also has two nephridia.[1][2][4][5]