D. nia)iiiiiiu is abundant in waters of the 

 southern United States. Ray (1966a) who sur- 

 veyed the occurrence of the fungus in the Gulf 

 of Mexico in 1961 and 1962, found infections 

 in 35 of 39 oyster samples, and prevalences as 

 high as 100 percent. Hoese (1964) was able to 

 find D. ma)i)iifni in the digestive tracts and 

 feces of fish, oyster drills, and crabs that had 

 fed on dying and dead infected oysters. He 

 speculated that transmission of the fungus 

 might be furthered by scavengers and that 

 scavengers may release the parasite from host 

 tissue. 



D. nmriiuou is common in oysters from most 

 high-salinity areas of the South Atlantic and 

 Gulf of Mexico coasts of the United States, but 

 is absent in a few such areas. Hoese (1963) 

 attempted assays of water samples from diflFer- 

 ent coastal locations in one section of the Texas 

 coast to determine their inhibitory effects on 

 development of fungus hypnospores. Although 

 results were not conclusive, water samples 

 from certain localities apparently stopped 

 hypnospore development. Hoese speculated that 

 the absence of D. marinum may be related to 

 those Spartina salt marshes where consistently 

 high salinities occur. 



In addition to its common occurrence in C. 

 virginica, Dermocustidium has been found in 

 other species. Ray (1954b) reported it in the 

 leafy oyster, Ostrea froiis L., from Florida and 

 in horse oysters, 0. eqitestris Say, from Texas. 

 The organism was not found, however, in the 

 mangrove oysters, C. rhizophorae (Guilding), 

 from Puerto Rico, in 0. echilis from Holland, 

 or in the rock oyster, C. commercialis (Iredale 

 and Roughley), from Australia. O. lurida (Car- 

 penter), the Olympia oyster, was experimen- 

 tally infected by exposure to infected C. 

 virginica. Dermocyf^tidium-Wke organisms have 

 also been seen in other mollusks I'.nd annelids. 

 Andrews (1955) found what he termed 

 "Dennociistidium-Uke" organisms in 12 of 16 

 mollusk species from the Chesapeake Bay area. 



This important fungus pathogen of oysters 

 continues to be the subject of much research. 

 Knowledge of its biology has been summarized 

 by Ray (1954b), Ray and Chandler (1955), 

 Andrews and Hewatt (1957), and Mackin 

 (1962). Mackin and Boswell (1956) proposed 

 a life cycle for D. mariimm that included a 



saprophytic stage leading to production of an 

 infective spore. Recently, Perkins and Menzel 

 (1966) described motile biflagellate stages that 

 were also postulated to be infective to oysters. 

 Mackin and Ray (1966) grew the organism on 

 beef-serum agar plates and suggested that it 

 belongs in the genus Labyrinthomyxa, a mem- 

 ber of the Labyrinthulales. Culture of a Denno- 

 cystidinm similar to D. mari)ii(»i in chemically 

 defined medium (Goldstein, Belsky, and Chasak, 

 1965) should make possible the study of isolates 

 from many areas to determine whether one 

 species or a species complex exists, and should 

 permit more precise determination of the taxo- 

 nomic affinities of the Dennocystidium. group 

 of protistan parasites. 



Korringa (1947, 1951a, 1951c) reported that 

 mortalities of the European oyster in Holland, 

 beginning in 1930, were caused by a fungus 

 disease characterized by formation of green or 

 brown pustules on the inner shell surfaces. 

 Activity of the fungus varied directly with 

 temperature, and the outbreak was said to be 

 intensified by widespread use of cockle shells 

 as spat collectors. Thin parts of oyster shells 

 were perforated by the di.sea.se agent, which 

 proliferated after reaching the interior sur- 

 faces. The fungus had been identified earlier as 

 a species of Monilia by Voisin (1931), who 

 found the infection, called ".shell disease," in 

 40 percent of oysters imported into France 

 from Holland in 1931. Cole (1950) and Cole 

 and Waugh (1956) found infections in the 

 European oyster from Brittany and in Portu- 

 guese oysters, C. migidatn (Lamarck), grown 

 in England. Infections were common in beds 

 where old shells were abundant. Cole and Han- 

 cock (1956) found the disease in almost all 

 beds of native European oysters, and described 

 two distinct forms : the typical one character- 

 ized by greenish rubbery warts and knobs on 

 the inside of the shell, particularly in the region 

 of the muscle attachment ; and an atypical form 

 in which young oysters had thickened shells 

 with numerous white patches but had no de- 

 formation of the muscle attachment area. 



Another di.sease of the European oyster, 

 which may be identical to shell disease, has 

 been misnamed "foot disease" or "maladie du 

 pied" (Dollfus, 1921a). It has long been known 

 on the coast of France; Giard (1894) described 



DISEASES OF THE MARINE BIVALVE MOLLUSCA AND CRUSTACEA 



339 



