Gangaichthys indonepalicus, a new genus and species of miniature stygobitic earthworm eel (Synbranchiformes, Chaudhuriidae) from alluvial aquifers in the Indo-Gangetic Plain, Bihar, northern India.

Gangaichthys indonepalicus gen. et sp. nov., is described from the Indo-Gangetic Plain, Bihar, India. This is the first stygobitic chaudhuriid and first subterranean fish from the alluvial aquifers of the Gangetic Basin and Indo-Gangetic Plain, with all three specimens collected from borewells. As the first subterranean member of the family Chaudhuriidae it is readily diagnosed from other genera and species of the family by a unique set of morphological characters linked to its stygobitic habit such as reduced eyes, the complete absence of body pigmentation, and apparent absence of ribs. In addition to its stygobitic characters, Gangaichthys is distinguished from all known chaudhuriid genera by the following osteological characters: neural spines laterally narrow and tapering to a point posteriorly or dorso-posteriorly, no spinelike projection on neural arch in front of neural spine; preorbital extension of ectopterygoid does not reach beyond coronoid process of dentary; metapterygoid elongate. Gangaichthys indonepalicus gen. et sp. nov. may further be distinguished from all known chaudhuriid genera and species by the presence of 64 vertebrae (28 abdominal, 36 caudal), and in having a single pectoral fin-ray, six caudal fin-rays, 37 dorsal, and 35 anal fin-rays. Molecular data place Gangaichthys indonepalicus gen. et sp. nov. within Chaudhuriidae, and it is > 20% divergent from two genera of the family for which there is comparative mitochondrial CO1 sequence data.