Praxillinicola kroyeri

Praxillinicola kroyeri —Type of a new family Praxillinicolidae

M’Intosh (1885) established the genus Praxillinicola for a new species found attached to the maldanid Praxillella abyssorum (M’Intosh, 1885) in the Antarctic Ocean. Having been collected at 3,510 m depth it constitutes one of the deepest records of a copepod associated with a polychaete host (Conradi et al. 2015). M’Intosh (1885) recognized a superficial similarity in body form between Praxillinicola kroyeri M’Intosh, 1885 and Rhodinicola elongata Levinsen, 1878 (he had no access to the description of the closely related and possibly congeneric Donusa clymenicola Nordmann, 1864). Since R. elongata had previously been included in the Clausiidae (Giesbrecht 1895; Wilson & Illg 1955) this misleading assertion led Southward (1964) to assign P. kroyeri to the same family. Rhodinicola elongata is associated with Rhodine gracilior Tauber, 1879 and R. loveni Malmgren, 1865, also maldanid polychaete hosts, but differs substantially (as M’Intosh admitted himself) in the morphology of the appendages and the reduced abdominal tagma. O’Reilly (1995) claimed that Praxillinicola has a caterpillar-like (eruciform) 9-segmented body with only the most rudimentary appendages present. On these grounds he excluded the genus from the nereicoliform group of families (sensu Gooding (1963)). Boxshall & Halsey (2004) considered Praxillinicola inadequately characterized and treated it as a genus inquirendum in the Clausiidae. Conradi et al. (2015) also listed P. kroyeri as a member of the Clausiidae. Redescription of the holotype below revealed some unique characteristics showing that Praxillinicola cannot be included in any of the currently recognized poecilostome cyclopoid families. Consequently, it is here fixed as the type of a new monotypic family.