Integrative taxonomy reveals a new unstriped Ichthyophis Fitzinger, 1826 from Vietnam and provides new data on diagnostic osteological traits for Asian tailed caecilians (Gymnophiona: Ichthyophiidae)

Abstract Herein we examined the cranial osteology of 15 species of Ichthyophis ( I. asplenius , I. beddomei , I. glutinosus , I. kohtaoensis , I. larutensis , I. mindanaoensis , I. multicolor , I. nguyenorum , I. nigroflavus , I. sikkimensis , I. singaporensis , I. supachaii , I. tricolor , I. weberi , and Ichthyophis sp. from northern Vietnam) with a special emphasis on the temporal region. We presented the first detailed description of the cranium and the atlas of an Ichthyophis species based on micro-CT scanning data. We discuss the implications of temporal region composition for the systematics of this group and the evolution of the cranium in Gymnophiona as a whole. We further provided comments on a jaw-closing mechanism and reported on the presence of phylogenetically basal cranial features in ichthyophiids that are also found in stem caecilians. Our detailed morphological description was based on a specimen from a previously unknown population of unstriped Ichthyophis from northern Vietnam. We consequently described this population as a new species based on morphological and molecular (3967 bp from cyt b , 12S rRNA, and 16S rRNA mitochondrial DNA genes) lines of evidence. We provide comparisons of external morphological traits of the new species with its congeners and further compare its cranial osteological features with other Ichthyophis for which skull descriptions exist. The new species differs from the morphologically similar species I. yangi and I. chaloensis by a significant divergence in cyt b and 16S rRNA mitochondrial DNA gene sequences (p = 6.5%–6.9% and p = 4.5%, respectively). The new species is currently known only from evergreen forests of Xuan Lien National Park (Thanh Hoa Province) and Pu Hoat (Nghe An Province) Nature Reserve, northern Vietnam, and was recorded at elevations of 700–800 m asl. We suggest the new species be considered Data Deficient (DD), following the IUCN’s Red List categories.