quently liberate uninucleate sporelike bodies. 

 The following detailed description of the species is 

 reproduced verbatim from Johnson and Sparrow 

 (1961, p. 539): 



Mature thallus a hyaline, spherical, spore-like body, 

 2-30m, averaging about 10m in diameter; each cell con- 

 taining a large, slightly eccentric vacuole in which a 

 polymorphic, refractive vacuoplast usually occurs; nucleus 

 oval, eccentric; cleaving internally to form a short hypha 

 terminated l)y an apical, conidium-like swelling. 



Dermocystidium can be identified on cross-sections 

 of an oyster stained with hematoxylin, Giemsa or 

 other histological stains, or in teased preparations 

 stained with Lugol solution (fig. 374). 



Identification of Dermocystidium by microscopic 

 examination of tissues is time consuming and 

 difficult. The diagnostic technique developed by 

 Ray, Mackin, and Boswell (1953) facihtates the 

 examination of large numbers of samples. Small 

 pieces of tissues are removed from the gaping 

 oysters and placed in Carrel tissue culture flasks 

 containing a small amount of sterile water to which 

 streptomycin and penicillin have been added to 

 prevent bacterial growth. Prior to excision the 



A. 



B. 



V 



Figure 374. — ^Drawings of Dermocystidium marinuni 

 stained with Heidenhain's iron hematoxylin and eosin. 

 A — A mature spore with markedly irregular vacuoplast, 

 cytoplasmic inclusions, and very large vacuole. B — 

 Multiple fission resulting in several daughter cells. C — 

 A binucleate stage with chromatin in diffuse condition, 

 and showing beginning vacuolation of the cytoplasm. 

 D — An immature .spore with small vacuole and vesicular 

 nucleus. Figure 1 from Mackin, Owen, and Collier, 

 Science, vol. Ill, No. 2883, 1950, p. 329. 



tissues are washed in sterile sea water, then placed 

 for 10 minutes in a 10 percent solution of sodium 

 merthiolate (1:10,000), waslied again in sea water, 

 and allowed to remain for several hours in sterile 

 sea water fortified with 1 ,000 units eacli of strepto- 

 mycin and penicillin. Tissues parasitized with 

 Dermocystidium disintegrate completely in about 

 a week, while in the controls they remain intact. 

 The debris of disintegrated tissues consists mainly 

 of minute spheres of Dermocystidium cells. Unfor- 

 tunately the contamination of samples with molds, 

 yeast, and ciliate protozoans could not be entirely 

 prevented and failures were "much more frequent 

 than were successes, and most of the experiments 

 were discarded." The data presented by Ray, 

 Mackin, and Boswell show that the major effect of 

 Dermocystidium infection is marked loss of weight, 

 averaging 33 percent. 



The infection may combine with other factors to 

 produce a mortality of oysters which, according to 

 IMackin (1961a), can virtually destroy seed oysters 

 planted in Louisiana in a single summer. Dermo- 

 cystidium studies in southern waters established 

 the significant fact that the effect of the parasite 

 "is not only a matter of disease but of season, 

 summer losses accruing from disease being signif- 

 icantly greater than those of early spring months" 

 (Ray, Mackin, and Boswell, 1953). The impor- 

 tance of environmental factors (temperature and 

 salinity) is clearly demonstrated by these findings. 



According to Mackm (1961b), the disease 

 caused by Dermocystidium affects the oysters from 

 Delaware Bay to Mexico but in the more northerly 

 part of the range is not apparent in winter. It is 

 not clear, however, if Dermocystidium remains in a 

 dormant stage or if it disappears from oysters. 

 In the Gulf States winter temperatures are prob- 

 ably not low enough to eliminate the parasite, and 

 consequently considerable mortality may occur in 

 mild winters. 



Dermocystidium marinum and possibly other 

 species of the genus have been reported from 

 0. frons, 0. eguestris, 0. lurida, Mya arenaria, 

 Mulina lateralis, Macoma baltica, Mercenaria 

 (Venv^) mercenaria, Anadare transversa, Anomia 

 simplex, Emis minor, Laevicardium mortoni, and 

 Lyonsia hyaliria (Johnson and Sparrow, 1961, p. 

 540). 



Many phases of tlie life history and biology of 

 Dermocystidium. require elucidation, particularly 

 the transport of spores by water and their pene- 

 tration into the tissues, the details of reproductive 



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