The phylogenetic position of an undescribed paedomorphic clupeiform taxon: Mitogenomic evidence

Molecular characters may offer a useful alternative to confidently estimate the phylogenetic position of paedomorphic taxa otherwise difficult to place based on morphology because of the reduction or absence of characters in their larvae-like adult stage. Here, we sequenced the complete mitogenome of a remarkable undescribed marine paedomorphic clupeiform fish to gain insight into its phylogenetic position. Of a length of 17,507 bp, this mitogenome exhibits a unique gene order within the Teleostei because of the inversion of the contiguous tRNA Gln and tRNA Ile within the IQM region and the presence of a putative second control region inserted between these tRNAs. Mitogenomic data from 27 clupeiform species and 22 non-clupeiform species were subjected to partitioned maximum likelihood and Bayesian analyses. All resultant phylogenetic trees strongly supported the placement of this undescribed taxon within the order Clupeiformes, suborder Clupeoidei, and the family Clupeidae, as the sister group of the tribe Spratelloidini ( Jenkinsia + Spratelloides ) of the subfamily Dussumieriinae. Together, they form a monophyletic group with Chirocentrus and, possibly, Etrumeus . Despite its overall resemblance to Sundasalanx , this undescribed taxa (Clupeidae gen. et sp. indet.) is not closely related to that genus and represents an independent paedomorphic lineage within the Clupeoidei.