FISHERY BULLETIN: VOL. 84, NO. 3 



Harpinia propinqua Sars. Both Types AA and AV 

 occurred in Rhepoxynius epistomus (Shoemaker) and 

 Unciola species (U. irrorata Say and U. inermis 

 Shoemaker), and only Type AV occurred in the re- 

 maining species (Table 1). Both types of syndinids 

 were present in Unciola species taken in a single 

 sample at station 35, but individual specimens were 

 parasitized by only one type. There are not enough 

 data to indicate whether or not incidence varies by 

 time of year in any of the amphipod species infected 

 with these parasites. Infected amphipods were not 

 found at the most northern and southern of the sta- 

 tions, but these stations were sampled fewer times 

 than most of the "positive" stations (i.e., stations 

 where amphipods with syndinid infections occurred). 

 There were 18 positive stations. Only Type AA was 

 found at stations 23, 37, and 50. Only Type AV 

 occurred at stations 33, 40, 56, and 62. Both types 

 were represented at stations 20, 27, 35, 38, 47, 48, 

 49, 51, 57, 63, and 64. 



Whether one or both types occurred at a single 

 station depended variously on which amphipod 

 species were present, and on unknown factors. Two 

 species of Ampelisca, A. vadorum Mills and A. 

 agassizi, were common at inshore station 33. Prev- 

 alence of Type AV in A. vadorum was 35% (56/158). 

 However, Type AA did not occur at station 33 

 although a favored host, A. agassizi, was abundant 

 there. In contrast, only Type AA was found at 

 station 23, no doubt because of 2,811 amphi- 

 pods collected there, only 23 were not A. agas- 

 sizi. 



Development and Morphology 



All forms were similar in that extensive plasmodia 

 were never present and chromosomes were con- 

 densed in the interphase nuclei of the spores. There 

 were four, possibly five, chromosomes. There was 

 no metaphase plate. At telophase the apices of the 

 two sets of chromosomes were touching (see Figure 

 3), and at all stages of mitosis the chromosomes of 

 each group were juxtaposed basally (where they 

 presumably were attached to the nuclear membrane) 

 and spread out apically to varying degrees, like the 

 spokes of a parasol (Figs. 2-4). These events are 

 typical of "mitose syndinienne" (Chatton 1921). Syn- 

 dinid chromosomes are V-shaped, so that each has 

 two arms. In tissue sections the V shape was best 

 seen in cells that had lysed, leaving only the chro- 

 mosomes (Fig. 5). During telophase there were often 

 only four (sometimes five?) visible arms of chro- 

 mosomes in each daughter nucleus. If sectioning 

 artifact was not responsible for the small number 









w 



*< 





m 



W 





M 



Figures 2-3.— Mitosis in Type AV parasites in Ampelisca 



vadorum (arrowheads). Interphase parasites of Figure 3 are 



stage II. 



Figure 4.— Mitosis in a Type AA parasite in Ampelisca agassizi 



(arrowhead). Chromosomes form a rosette in the interphase 



nucleus to the right (asterisk). 



Figure 5.— Chromosomes in a lysed Type AA parasite from 



Byblis serrata (arrowhead). The V shape of the chromosomes 



is evident. Figures 2-5, x 1500. 



of visible arms, the cells might have been haploid. 

 Before spore formation, chromatin disposition in 

 nuclei was variable, depending on the type of 

 parasite and the stage of development. Resting 

 nuclei with unfolded chromosomes were granular or 

 vesicular, and sometimes rimmed with chromatin 

 (see Figures 8, 17). In nuclei with partially unfolded 

 chromosomes, clumps of chromatin often were ar- 

 ranged so that they created a dashed or dotted line 

 in the position that would be occupied by a complete- 

 ly condensed chromosome (see Figure 9). When seen 

 in a polar view, chromosomes or chromatin clumps 

 formed rosettes (Figs. 4, 5). Morphology of the per- 

 sistent chromosomes of spores was variable and will 

 be described later. 



608 



