Redescription of alien nematode, Rostellascaris spinicaudatum (Malhotra and Anas, 2001) of evolutionary significance with revised key to the family Raphidascarididae Hartwich 1954.

Abstract

The redescription of Rostellascaris spinicaudatum has brought to focus Scanning Electron microscopic evidence of evolutionary consequence. The intestinal caeca, ventriculus and ventricular appendix of family Anisakidae; ventriculus and ventricular appendix of family Raphidascaridae; and along with it, post-cloacal collarette of family Physalopteridaein worms recovered from coral-reef associated fish hosts at 'Grande' island, evidently confirmed that the characters of as many as three families were encountered in R. spinicaudatum. The selective adaptation of these specific characters exhibited significant evolutionary trend, and indeed these could radiate connecting link features of Raphidascarididae. Additionally, an inversely bifurcated interlabia on head and pre-cloacal as well as specialized lateral 'sunflower' papillae comprised significant taxonomic information on systematics of ascaridoid (raphidascaridid) nematodes. Interestingly, these worms equipped with remarkably advanced features parasitized primitive host group like, Pisces, in the series of vertebrates, contrary to the characteristics of co-evolution in which parasitizing organism gradually acquired advanced features as it progressed up the ladder of evolution (from Pisces to Mammalia). In the parasitic world, therefore, the worm like Ancylostoma with its occupancy in the highly evolved group i.e. mammals obviously exemplified 'co-evolution', while on the contrary 'Reverse Co-evolution' was the event that was encountered in R. spinicaudatum.