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PRESUMED PARASITIC TRENDS IN THE EVOLUTION OF THE FAMILY CYCLOPIDAE (COPEPODA, CYCLOPOIDA)

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In the present paper, a morphological analysis of four species (from two genera of the family Cyclopidae) with modified maxillae and maxillipeds is presented, and the modifications observed are interpreted in a functional sense. The genera at issue are Sergiosmirnovia with S. reducta, its type species, and S. unisetosa; and Colpocyclops with C. dulcis, its type species, and in addition C. longispinosus. The taxa examined belong to the subfamily Halicyclopinae and inhabit the mouth and lower reaches of the river Dnieper, the so-called “limans” of the Dniester River, and the Caspian Sea. Modifications in structures of the maxilla in these four species are compared with the structures found in all four subfamilies of Cyclopidae. The maxillae are strongly developed (i.e., enlarged), and oligomerized, with some segments fused or reduced, and also some setae enlarged or reduced. For example, the praecoxa and coxa are fused to form a syncoxa, lacking any trace of a distal endite. The basis of the maxilla in the four species is grossly enlarged and drawn out into a powerful claw that has an apical position, and which is of a prehensile type. Only some setae, as judged from their morphology, can be presumed to have retained a tactile function. The maxillipeds are reduced to a one-segmented vestige bearing only two setae.As members of the Cyclopidae, these species represent apparently rare developments into what may be surmised to comprise an either parasitic, or else commensal mode of life, and originating from an otherwise free-living group of copepods: a unique phenomenon within the Ponto-Caspian zoogeographic region. The adaptation to a parasitic mode of life is expressed first and foremost in the modification of the substantially enlarged basis of the maxilla. With regard to the possible functions of these modified structures, it is suggested that they play a role in attaching the copepod to its (as yet unknown) host. This supposition is analogous to assumptions about the functioning of similar morphological structures in Eucyclops bathanalicola, another cyclopid parasite, as well as to comparable deductions made from structures found in fossil forms.

10.1163/9789004188280_016
/content/books/b9789004188280s016
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