1963), the Mediterranean Sea (Bassedas, 1950; 

 Meyer- Waarden and Mann, 1953), and the 

 Adriatic Sea (Steuer, 1902; Pesta, 1907; 

 Meyer- Waarden and Mann, 1953). Waugh 

 (1966) has mapped the recent distribution of 

 the parasite in northern Europe. A conference 

 to review and discuss problems of parasitiza- 

 tion by Mjitilicola was held in Paris, and the 

 proceedings were published in 1951 (Cole, 

 1951a; Dollfus, 1951; Havinga, 1951; Heldt, 

 1951 ; Korringa, 1951b; Korringa and Lambert, 

 1951; Lambert, i951a, 1951b; Leloup, 1951; 

 Meyer and Mann, 1951). It was agreed that 

 Miitilicola constituted a severe threat to the 

 mussel industry of Europe, but whether the 

 copepod was a direct or indirect cause of death 

 was left undecided. Continuing mortalities as- 

 sociated with the presence of Mytilicola 

 (Brienne, 1964), however, indicate a causal 

 relationship, possibly influenced by stre.sses of 

 spawning, high temperatures, and inadequate 

 food supply. 



Another species, Mijfilicola porrecfa Humes, 

 occurs in ribbed and recurved mussels (Modio- 

 liiK dcniissns Sowerby and Mytihis recurvus 

 Rafinesque) in the Gulf of Mexico. Humes 

 (1954) found as many as 15 individuals per 

 mussel, but no pathology or mortality was indi- 

 cated. A third species, Mytilicola orientalis, 

 known to occur in Mytihis ediilis and M. crassi- 

 tcsta, was recently reported from the California 

 mussel by Chew, Sparks, and Katkansky 

 (1964). 



Pinnotherid crabs of several species, best 

 known as parasites of oysters, also occur in 

 mussels. McDermott (1962) found that Pin- 

 notheres ostreinn and P. macidatus cause gill 

 damage and palp erosion in M. ednljs. Earlier, 

 Atkins (1931b) described similar palp abnor- 

 malities in mussels from England. 



CLAMS 



Many species of bivalves called by the gen- 

 eral term "clam" are harvested throughout the 

 world. Some species constitute a significant 

 commercial crop in many coastal areas ; other 

 species are fished for sport or are ignored. 

 Changes in clam abundance have been docu- 

 mented, although mass mortalities comparable 

 to those in oysters and mussels have not been 

 reported. Mass deaths may pass unnoticed in 



-sediment-hidden clams ; it may be for this rea- 

 son that information on diseases of clams is 

 scarce. Among the diseases and parasites that 

 are known in clams are: several protistan or- 

 ganisms, larva! trematodes, larval cestodes, 

 parasitic copepods, and tumors. 



Microbial Diseases 



Coe's (1955) study of population fluctuations 

 of the California bean clam, Doiia.v gouldi Dall, 

 included a description of a possible fungus para- 

 site "apparently similar to Dermocystidium 

 marinmn" as a cau.se of mass mortalities during 

 the summer. Moribund clams of all ages were 

 heavily infected with "irregularly spherical or 

 ovoid cells, 2 to 6 microns in diameter." The 

 identity of the pathogen was not further de- 

 termined, however, and the information pre- 

 sented is insufficient to identify it as a 

 Dermocystidium. 



Much earlier, Leger (1897) found a coccid- 

 ian, Hyalokiossia pelseneeri, in kidneys of 

 Doiiax sp. and Tellina sp. in Europe, and Leger 

 and Duboscq (1917) described another coc- 

 cidian, Pseudoklossia glomerata, parasitic in 

 Tapes floridus L. and T. virgineus L. from the 

 Mediterranean Sea. 



Ciliate parasites have been described from 

 soft-shell clams, Mya aroiaria L., by Uzmann 

 and Stickney (1954). The peritrich Trichodina 

 myicola Uzmann and Stickney was found, often 

 in large numbers, on the palps. These infections 

 were often accompanied by the nonpathogenic 

 thigmotrich Aiicistrocoma myae (Kofoid and 

 Busch). A. myae had been described earlier 

 from M. arenaria sampled in California 

 (Kofoid and Busch, 1936; Kozloff', 1946) and 

 in Massachusetts (Chatton and Lwoff', 1950). 

 Kozloft' considered the ciliate identical to A. 

 pelsciieoi, a common parasite of sea mussels. 

 Fenchel (1965) also found Ancistrocoma myae 

 in nearly 100 percent of M. arenaria sampled 

 from two locations in Denmark. 



Diseases Caused b>- Helminths 



Several life history stages of diverse trema- 

 todes occur in the soft-shell clam. Uzmann 

 (1952) reported sporocysts and cercariae (Cer- 

 caria myae) from gonads and digestive gland 

 of this clam from Massachusetts, and held that 

 parasitization resulted in a condition known as 

 "water belly." (Subsequent observations, sum- 



DISEASES OF THE MARINE BIVALVE MOLLUSCA AND CRUSTACEA 



349 



