Hydrolagus

Lewis A. K. Barnett, Dominique A. Didier, Douglas J. Long & David A. Ebert, 2006, Hydrolagus mccoskeri sp. nov., a new species of chimaeroid fish from the Galápagos Islands (Holocephali: Chimaeriformes: Chimaeridae)., Zootaxa 1328, pp. 27-38 : 27-28

[[ Hydrolagus ]]

Introduction

Chimaeroids are the extant members of the subclass Holocephali (living and fossil chimaeras or ratfishes) which, together with the Elasmobranchii (sharks, skates and rays), form the monophyletic class Chondrichthyes (Didier 1995; Grogan & Lund 2004; Maisey 1984, 1986; Schaeffer 1981). Their distribution is cosmopolitan with the exception of the Arctic and Antarctic oceans. At present there are 34 species described in the order Chimaeriformes (Compagno 2005), with as many as ten new species awaiting formal description, all within the family Chimaeridae (Didier, unpublished data). One additional species, Hydrolagus lusitanicus Moura et al. 2005 , was recently described but it remains unclear whether or not this is indeed a valid species (D.A. Didier, personal observation). The Chimaeridae are the largest family of the order, consisting of two genera, Chimaera and Hydrolagus . The Hydrolagus are more speciose and differentiated from Chimaera by the absence of a notch separating the anal fin from the ventral caudal fin.

Species richness of Hydrolagus is greatest in the western Pacific, with 11 known species. The eastern Pacific fauna consists of only two described species, Hydrolagus colliei (Lay & Bennett 1839) and H. macrophthalmus de Buen 1959 . The former is endemic to the eastern North Pacific (Allen & Smith 1988; Didier & Rosenberger 2002; Eschmeyer et al. 1983; Miller & Lea 1972), while the latter seems to be restricted to the eastern South Pacific. The only confirmed records of H. macrophthalmus are from off Chile (de Buen 1959), however, reports of this species from off Peru (Chirichigno 1968) may also be accurate (Quaranta et al. in review). The new species described in this study marks the first record of a chimaeroid from the Galápagos Islands (Grove & Lavenberg 1997).