Intraspecific variation in the caudal papillae of Raphidascaris mundeswariensis (Nematoda: Raphidascarididae) from gobiiform fishes in eastern India.

The morphological variation of the nematode Raphidascaris mundeswariensis Patra, Choudhury, Thorn et Ash, 2021 in four fish hosts, Apocryptes bato (Hamilton), Glossogobius giuris (Hamilton), Taenioides cirratus (Blyth) and Eleotris lutea (Day), from the Mundeswari River of West Bengal, India, was studied. Partial sequences of the 28S rRNA and COI gene were generated to verify the conspecificity of these isolates while evaluating host-related variation in these samples. Little to no genetic variation was found among isolates from the different hosts and all were identified as R. mundeswariensis. However, subtle differences were found in the morphology among specimens of R. mundeswariensis from the four different hosts, mainly the number of caudal papillae and spicule length. The difference in the nematode morphology from various fish species can be a case of host-induced morphological variation which may enhance the adaptive capabilities of these helminths to parasitise a wide range of hosts. The present study raises questions about the use of the number of caudal papillae as an important taxonomic character in this species and other related nematodes. The results from this study also highlight the importance of examining as many specimens as possible from different hosts in the same localities to cover the range of intraspecific variation.