[The peculiarities of parasitism in the copepoda and rhizocephala]

Abstract

In the parasitology it is accepted to subdivide the parasites into two categories based on their spatial relations with the organism of a host. To first category--ectoparasites--includes organisms, which live "on external covers, on a skin, on gills". To the second category--endoparasites--includes organisms living "in internal cavities, tissues and cells of the host" (Dogiel, 1941). Feizullaev (1971) offered the third category--mesoparasites--where he placed "the parasites inhabiting places, which are connected to cavities being open to external environment". According to him the places are oral, nasal, eye cavity, cloaca etc. Since some parasitic copepods living in certain kind of interrelation with a host can be referred neither to ectoparasites nor to endoparasites, the author offers these following criteria for the mesoparasitism definition. 1. Morphological and anatomic subdivision of the body of the parasite into two main parts: ectosoma located in the external environment (environment of the second order) and endosoma located inside the organism of the host (environment of the first order). 2. Functional subdivision of parasite body into two parts: endosoma which performs the trophic function and ectosoma with genital organs performs the reproduction function. 3. Existence of the parasite on the border of two environments (of the first and second order) which have an influence on parasite directly and simultaneously. The mesoparasites are known among the parasitic Copepoda and Rhizocephala only. As for the copepods all members of the family Herpyllobiidae may be placed in this category; the members of the families Phyllodicolidae and Chitonophilidae may be also included in it, albeit tentatively (because their anatomy has not yet been adequately studied), as well as five genera of the family Nicothoidae (Aspidoecia, Cephalorhiza, Diexanthema, Nicorhiza and Rhizorhina), and Bradophyla pigmaea.