ABSTRACT
The phylum Nematoda was divided into two classes: Adeonophorea and Secernentea. Despite constituting 41%, the free-living nematodes have not received much attention, in comparison to parasitic nematodes. Examining 40,000 specimens over a period of 4 years, Lancaster and Bovill estimated the prevalence and intensity of multiple mermithids on six congeneric host caddisflies of Ecnomus. Prevalence and intensity of nematode infection may depend on a number of factors such as fecundity, inclusion of IH and their motility, as well as host susceptibility and density. In most nematodes, sex determination is strictly genetic but it may be primarily genetic with environmental (parasitic intensity) modulation at the downstream levels of genetic cascade of sex differentiation. In Contraecum incurvum, the identified Y-chromosome is paired with a long X-chromosome. However, there are also 7 univalent X-chromosomes.
