Geometric morphometrics uncovers a new species of ponyfish (Teleostei: Leiognathidae: Equulites), with comments on the taxonomic status of Equula berbis Valenciennes

Abstract

A new species of Equulites is revealed using geometric morphometric techniques and is herein described. Based on features recovered in recent comparative analyses, members of Equulites have been diagnosed on the basis of internal and external male-specific traits related to their light-organ system (LOS; Sparks et al., 2005; Sparks, 2006; Sparks and Chakrabarty, 2007; Chakrabarty and Sparks, 2008). These sexually-dimorphic traits are hypothesized to allow males to signal to conspecific females in photic sexual displays using bacterially-generated luminescence (Woodland et al., 2002; Sasaki et al., 2003; Wada et al., 2005). The holotype and sole name-bearing type of Equulites leuciscus (BMNH 1858.4.21.243, 104.9 mm SL) is an adult female, and therefore lacks the diagnostic external feature of the LOS, a large, translucent flank patch, used to identify species in this genus. Geometric morphometric shape analysis of individuals ascribed to Equulites leuciscus, a traditionally widespread, "catch-all" taxon, reveals two discrete shape groups. Based on the results presented below, members of one of these groups correspond to a morphological variant that represents the new species (Equulites absconditus Chakrabarty & Sparks) described herein, whereas the other group corresponds to traditional E. leuciscus. In addition, the taxonomic status of Equula berbis Valenciennes, to which many female and poorly preserved specimens of the new species have erroneously been attributed, is reviewed and E. berbis is concluded to be a nomen dubium of uncertain placement beyond the family level.