What is the difference between marine and limnetic-terrestrial associations of nematodes with invertebrates?

Abstract

Zoo- and phyto-parasitic nematodes of the order Rhabditida and zooparasites of the subclass Dorylaimia are well known, due largely to their medical, veterinarian and agricultural significance. However, there have been many switches from a free-living to a symbiotic (including parasitism) mode of existence in the evolutionary trajectories of various nematode clades. Here, we attempt to summarize all known cases of symbioses (from commensalism to true parasitism) between marine nematodes representing nonparasitic taxa and various larger animals, ranging from protists to vertebrates. Most cases are of nematodes relating to dwelling on crustaceans (ectocommensalism) or living in the body cavity and internal organs of various invertebrates (endoparasitism or parasitoidism). Ectocommensal species may differ from their free-living relatives in their longer filiform bodies and enlarged ventral and caudal glands, which may be interpreted as adaptations for the purpose of fixation on the body surface of a motile host. Endoparasitic species are characterized by deep anatomical modification, including rudimentation of the alimentary tract and hypertrophy of reproductive organs. Unlike terrestrial and limnetic invertebrates, marine invertebrates have almost no intestinal nematode dwellers. The evolutionary trajectories of nematode dwellers of marine and nonmarine invertebrates are compared.

Keywords: Nematoda; commensalism; marine invertebrates; parasitism; symbiosis.