A nematode in a haystack: rediscovering ascarophis morrhuae van beneden, 1871 (Cystidicolidae), a parasite of atlantic cod, gadus morhua linnaeus, 1758 in the Eastern Atlantic

Abstract

Nematodes belonging to the Cystidicolidae constitute more than 23 genera of 111 poorly known species in fish from many habitats including the deep-sea, continental shelves, estuarine and freshwater habitats. The taxonomy of many species within the Cystidicolidae is unsettled due to their small size and equally small morphological characters requiring use of SEM and supported more recently by molecular studies. Most significantly, the type species, Ascarophis morrhuae van Beneden, 1871, which is the oldest and most speciose genus with over 55 species, is based on a two- sentence description of a single female specimen from an Atlantic cod, Gadus morhua, presumably off the coast of Belgium in the North Sea. Through a research grant from Hasselt University, Belgium, attempts were made to find type material, additional material including trawling in the North Sea, obtaining fish from Belgium fish markets, and examining preserved specimens in the British Museum of Natural History. This study establishes the morphological and genetic identity of A. morrhuae, differentiates it from other species, and validates the accuracy of two salient morphological features used by van Beneden to establish this species and the genus Ascarophis. This information will provide a basis for a taxonomic reconsideration of all cystidicolid nematodes, including those genera and species present in the Eastern Pacific.