Comparative studies on Rhabdiasoid Nematodes

Abstract

The present study was undertaken to try to produce a better understanding of an unusual group of nematodes, viz. rhabdiasoids, in which parasitic and free-living generations alternate. The introduction defines rhabdiasoid nematodes, viz. family Rhabdiasidae, genera Rhabdias, Entomelas, Ophiorhabdias, Pneumonema, Haplospironema, Acanthorhabdias; family Strongyloididae, genera Stronayloides, Parastrongyloides; reviews the present knowledge of the group; considers the main problems associated with understanding the group; examines the approaches used previously to study nematodes and defines the approaches used in this study. Species from all the above genera except Acanthorhabdias were studied. Material and methods outlines the material used and how it was maintained. All techniques including preparation of material and recording methods are described. The results are divided into the following sections: morphology of parasitic adults, including a historical review of the generic name; life-cycle pattern; life-cycle developmental morphology; post-embryonic development of the reproductive system. In each section Pneumonema tiliquae is described in detail, then individual species of the other genera are described, comparing them where possible with P. tiliquae. Where necessary introduction, remarks and discussion are included in each section. In an endeavour to compare as many morphological and life-cycle features as possible, the study does not include detailed information of some aspects of development, e.g. histochemistry of the lateral cords; regions of the intestine in the parasitic generation and detailed host specificity experiments. The technique used required fresh material, consequently examination of type material was of limited value. In the final part of the thesis the free-living and parasitic generations are compared; the free-living generation is compared with free-living rhabditid nematodes and general conclusions are considered. The thesis ends with a summary of all results. Each family formed a uniform group with each genus having some characteristic morphological and life-cycle features. The two families appeared distinct with the Strongyloididae having nuclei with an unusual staining appearance and an apparently unique method of gametogenesis.