Chimaera compacta, a new species from southern Indian Ocean, and an estimate of phylogenetic relationships within the genus Chimaera (Chondrichthyes: Chimaeridae)

Chimaera compacta sp. nov., a new species of shortnose chimaera (Holocephali: Chimaeriformes: Chimaeridae), is described from a single specimen collected at 595–655 m depth, off Amsterdam Island, in the southern Indian Ocean. The species is easily distinguished from its congeners by the combination of the following characters: massive head with short snout; stocky and relatively long trunk 44% BDL, short tail with second dorsal fin base 72% BDL; long pelvic fin anterior margin 26% BDL. Caudal fin dorsal origin slightly posterior to caudal fin ventral origin. Firm, non-deciduous skin; brown color with yellow blotches. Chimaera compacta sp. nov. is morphologically close to Chimaera lignaria Didier 2002 from New Zealand and Chimaera willwatchi Clerkin, Ebert and Kemper 2017 from south western Indian Ocean. The new species can be distinguished from other Chimaera species based on DNA sequences divergence of the COI and NADH2 genes. This species has a nucleotide sequence divergence (uncorrected p distances) for the studied genes of 4.2 and 4.1%, respectively, with its closest relatives. Phylogenetically, Chimaera compacta sp. nov. is nested within a well-supported group including Chimaera carophila Kemper, Ebert, Naylor and Didier 2014, Chimaera didierae Clerkin, Ebert and Kemper 2017, C. lignaria, Chimaera macrospina Didier, Last and White 2008, Chimaera notafricana Kemper, Ebert, Compagno and Didier 2010, Chimaera opalescens Luchetti, Iglésias and Sellos 2011, and C. willwatchi. It is the first Chimaeridae described for the Territory of the French Southern and Antarctic Lands.