The phylogeny of Halgerda (Opisthobranchia, Nudibranchia) with the description of a new species from Okinawa

This paper proposes a refined hypothesis of evolution for the tropical Indo -Pacific nudibranch genus Halgerda. Numerous specimens from 31 species were examined anatomically and literature from four additional species was revi ewed, bringing to 33 the ingroup taxa. Fifty-three characters were consider ed from these examinations. The outgroup Asteronotus was used to polarize t he characters. The phylogeny obtained from the analysis of the characters s upports the hypothesis that Halgerda is a monophyletic group. A species pre viously placed with the genus Sclerodoris is examined and determined to be a member of the genus Halgerda. Phylogenetic analysis places this species, H. paliensis, as a basal member of the genus. Halgerda paliensis appears to be restricted to the Hawaiian Islands. Specimens previously identified as Sclerodoris paliensis from the Marshall Islands actually represent H. dalan ghita Fahey & Gosliner, 1999. A new species, Halgerda onna, is described an d presented as the sister taxon to a basal member of the genus. A range and depth extension of a previously described species, H. malesso, is presente d. The present phylogeny is then compared to previous studies, in particula r those of Fahey & Gosliner (1999a,b).