Redescription of a rare cusk eel, Pycnocraspedum squamipinne (Actinopterygii, Ophidiiformes, Ophidiidae), from Bay of Bengal

Pycnocraspedum squamipinne Alcock, 1889 is a rare species of pelagic cusk eel described from specimens collected off the Bay of Bengal. The descriptive literature on P. squamipinne is limited to the original description owing to the rarity in collections. The genus and the species need a thorough revision to identify specific characters of taxonomic importance as the descriptive information regarding the species in the genus Pycnocraspedum is limited to the holotypes and syntypes. Fifteen fresh specimens of P. squamipinne were collected from the Chennai coast, Tamil Nadu, Bay of Bengal region. The syntypes of P. squamipinne (ZSI F 11700 and ZSI F 11703) available at the Zoological Survey of India, Kolkata were examined. The morphometric and meristic characters of P. squamipinne were compared with those of syntypes and other species of the genus. Molecular analysis was carried out using partial mtDNA cytochrome oxidase subunit I gene (COI). The specimen is deposited in the national fish repository of the ICAR, National Bureau of Fish Genetic Resources, Lucknow, India. A detailed redescription of P. squamipinne based on the syntypes and fifteen recently collected specimens are provided. A detailed comparison with other species of the genus is also provided which helps in establishing the taxonomic identity of P. squamipinne. Molecular information was generated which would help in the species identification of this rare deep-sea species. This study provides morphological and molecular information of the rare cusk eel, P. squamipinne, which would help in the precise identification of the species. However, due to paucity, the majority of species of the genus are still only known from single specimens and comprehensive examination of holotypes and intensive sampling is needed to better understand the species identity and distribution.