ciliates is necessary for firm identification (Corliss 

 1979), the amphipod ciliates can be only provision- 

 ally assigned to a ciliate group, as is true in other 

 studies based on fixed and embedded material 

 (Sparks et al. 1982; Hibbits and Sparks 1983). On 

 the basis of similarities in hosts and morphology, the 

 amphipod ciliates discussed here are like the apos- 

 tome genus Collinia, whose members parasitize am- 

 phipods (Summers and Kidder 1936; de Puytorac 

 and Grain 1975). Like Collinia, size of individual 

 ciliates from the benthic amphipods varied greatly 

 and there was no indication that the ciliates were 

 phagocytic Paranophrys and Parauronema, on the 

 other hand, belong to a group that ingests particu- 

 late material. Paranophrys is known to ingest 

 hemocytes and other cells of its hosts, and does not 

 exhibit major size differences (Bang 1970; Sparks 

 et al. 1982; Hibbits and Sparks 1983). Provisionally, 

 the ciliates of benthic amphipods are being con- 

 sidered apostomes. 



Whether more than one species of ciliate was in- 

 volved in the infections is uncertain, but probably 

 the ciliate of Pontogeneia inermis represented a 

 species apart from the others. Its very large forms 

 with the ribbonlike macronucleus were not dupli- 

 cated in other infections. 



Although more A. agassizi were found infected 

 with ciliates than any other species of amphipod, this 

 was apparently because it was the most abundant 

 and widespread of the susceptible species sampled. 

 A. agassizi had the lowest overall prevalence of ciliate 

 infection and sometimes was not parasitized when 

 other species in the same samples were parasitized. 

 There are at least two possible explanations for the 

 odd host distribution of the amphipod ciliates. First, 

 the ciliates might be highly host specific, each am- 

 phipod species having its own species of ciliate Sec- 

 ond, the ciliates might be either primary parasites 

 of some other member(s) of the benthic community, 

 or incompletely adapted to a parasitic existence, and 

 thus only occasionally parasitizing the least resis- 

 tant species of the sampled amphipods. Unciola 

 species and Leptocheirus pinguis were often the 

 most abundant amphipods at certain stations, but 

 ciliates were never found in individuals of these 

 species, suggesting that they are resistant to ciliate 

 attack. Conversely, the relatively high prevalence of 

 ciliates in the rare species of amphipods could in- 

 dicate less resistance than is exhibited by most of 

 the species of amphipods sampled. 



Presumably, infected amphipods would eventually 

 die of their ciliate infections because of the massive 

 loss of hemocytes. The infrequency of ciliate infec- 

 tion, except in certain rare species, indicates that 



these parasites are not important in regulating the 

 general amphipod populations they infect. 



Acknowledgments 



Thanks are due the following: Frank Steimle and 

 Robert Reid of the Northeast Fisheries Center, 

 Sandy Hook Laboratory, and Linda Dorigatti, Gret- 

 chen Roe, and Sharon MacLean of the Oxford 

 Laboratory collected the amphipods; Ann Frame, 

 Sandy Hook Laboratory, provided advice and train- 

 ing in identification of amphipods; Linda Dorigatti 

 identified material from cruises A to C, and she, 

 Gretchen Roe, Dorothy Howard, and Cecelia Smith, 

 Histology Section, Oxford Laboratory, prepared the 

 specimens for histological examination. 



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