Two new species of Musellifer (Gastrotricha: Chaetonotida) from Florida and Tobago and the systematic placement of the genus within Paucitubulatina

Two new species of marine Gastrotricha, Musellifer reichardti sp. nov. and Musellifer tridentatus sp. nov. (Chaetonotida: Paucitubulatina: Muselliferidae), are described from the Atlantic coast of Florida (USA) and the west coast of Tobago (Trinidad and Tobago), respectively. Both new species are peculiar in that they lack a muzzle bearing the mouth, which is a diagnostic character of the genus. They correspond well to the diagnosis of Musellifer in other morphological features, and genetic data from the 18S rDNA gene of M. reichardti sp. nov. further support the inclusion of the new species in the genus Musellifer. Musellifer reichardti sp. nov. is distinguished by the following combination of characters: blunt head with reduced muzzle; dorsal patches of naked cuticle bearing sensory cilia on either side of the head; ventral locomotory cilia restricted to the pharyngeal region; spined scales; caudal furca with naked adhesive tubes. The new species is a simultaneous hermaphrodite with posterior paired ovaries, paired testes located at mid-body length, and a posterior frontal organ. M. tridentatus sp. nov. is the first species within the genus exhibiting two types of dorsal/lateral scales: anteriormost dorsal and lateral trident-shaped scales and smooth strongly overlapping dorsal scales. The systematic placement of Musellifer within the Paucitubulatina is discussed and emended diagnoses are given for Muselliferidae and Musellifer.