FISHERY BULLETIN: VOL. 84, NO. 3 



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Figures 13-17.— Type AV parasites. 13: Stage III (spores) in 

 Leptocheirus pinguis. The chromosomes are spherical (arrow- 

 head). 14: Stage II in Monoculodes edwardsi. Two of the para- 

 sites are polyploid (arrowheads). Note separate groups of 

 chromosomes or chromatin clumps in both these parasites. 15: 

 Plasmodium resulting from nuclear division of a polyploid 

 parasite in M. edwardsi. Note differently sized nuclei. 16: Stage 

 III (spores) in M. edwardsi. There were flagellated spores in this 

 infection. 17: Prespores, some dividing, in M. edwardsi. A 

 Plasmodium, with rimmed nuclei, is also present (arrow- 

 head). Figures 13-17, x 1500. 



with Type AV organisms, and karyorrhexis had oc- 

 curred in unidentified cells in the area. With the 

 possible exception of the Type AV infection in L. 

 pinguis, the syndinids were not being attacked by 

 hemocytes at the time of fixation. 



There was another sign that the syndinid parasites 

 successfully evaded detection by their hosts. Two 

 specimens of A. agassizi, both collected at station 

 47 but at different times, were infected jointly and 

 heavily with Type AA and an unidentified fungus 

 (Fig. 7). Of the more than 7,000 examined micro- 

 scopically, these were the only two amphipods that 

 had systemic fungal infections. Fungi were being 

 phagocytized by hemocytes and fixed phagocytes, 

 and other groups of fungi were being transformed 

 into melanized nodules. (Probably the latter fungi 

 had originally been phagocytized and killed by 

 hemocytes that did not survive the process them- 

 selves.) Although hemocytes and fixed phagocytes 

 were actively destroying fungi, there was no indica- 

 tion that the accompanying syndinids were recog- 

 nized as foreign. 



Numbers of hemocytes apparently decreased dur- 

 ing syndinid infection, but even in heavy infections 

 some hemocytes remained and were still functional 

 as shown by their ability to phagocytize the fungi 

 discussed above. It is probable that the two suc- 

 cessful fungal infections in syndinid-infected amphi- 

 pods resulted in part from the fungi multiplying 

 more rapidly than they could be phagocytized and 

 degraded by the few remaining hemocytes and the 

 fixed phagocytes associated with the heart. 



The syndinid parasites did not castrate their hosts. 



Whether death ensues from every infection with 

 these parasites is not known. However, the general 

 lack of discernible host response makes it unlikely 

 that amphipods could successfully combat the 

 parasites. 



DISCUSSION 



Like species of Syndinium described from cope- 

 pods, Types AA and AV have a small number of 

 chromosomes which are permanently condensed in 

 spores and partially condensed in certain other 

 stages; plasmodia (small and multiple in the case of 

 Types AA and AV) are present during some devel- 

 opmental stages; and spore formation takes place 

 in the hemocoel of the host. However, species of 

 Syndinium in copepods differ from Types AA and 

 AV in that they develop from a Plasmodium that is 

 first applied to the wall of the gut and then expands 

 to fill the entire hemocoel. The massive Plasmodium 

 then fragments to form individual dinospores. By 



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