Osteology of a Monopterusa roseni with the description of Rakthamichthys, new genus, and comments on the generic assignment of the Amphipnous Group species (Teleostei: Synbranchiformes)

Abstract

We provide a detailed description of the head and shoulder girdle osteology of the holotype of the synbranchid ‘Monopterus’ roseni Bailey & Gans. Collected from a well in Kerala, this subterranean synbranchid shows a number of unique and highly derived characters in the gill arch skeleton. In ‘Monopterus’roseni, basibranchial 2 does not articulate with basibranchial 1, but is situated more posteriorly between the proximal ends of hypobranchials 2, with which it articulates; and ceratobranchial 2 does not articulate with hypobranchial 2, but is offset posteriorly so that the distal tip of hypobranchial 2 is situated in between the proximal ends of ceratobranchial 1 and 2. Based on these striking osteological differences and a combination of additional diagnostic characters, we erect the new genus Rakthamichthys with the type species Monopterus roseni. We also include the other two southern Indian subterranean species formerly referred to as M. indicus Eapen (= M. eapeni Talwar) and M. digressus Gopi in the new genus Rakthamichthys along with the northeast Indian M. rongsaw Britz, Sykes, Gower & Kamei. Rakthamichthys also differs genetically from the other Asian genera of synbranchids, Monopterus and Ophichthys, by an uncorrected p-distance of 18.9-23.9 % in the cox1 barcoding gene. We further resurrect the genus name Typhlosynbranchus Pellegrin for the two West African species ‘M.’ boueti and ‘M.’ luticolus.