with those caused by bacteria (virus diseases, 

 with but a single exception (Vago, 1966), have 

 not been identified in marine invertebrates) 

 and progressing to fungi, pi'otozoans, and 

 larger parasites, has been followed. Often a 

 host species may be infected by several well- 

 defined pathogens, as well as assorted parasites 

 that have variable impact on the host popula- 

 tion. The common and the scientific names of 

 parasites and hosts are usually both given when 

 the organisms are first mentioned in the text, 

 after that either one may be used. 



No general review has been made of the 

 literature on diseases of marine invertebrates 

 (Steinhaus, 1965), but particular groups — 

 especially those of commercial importance — 

 have received some attention. Dollfus (1921a), 

 Pel.seneer (1928). Ranson (1936), and Fischer 

 (1951) have summarized information about 

 the parasites and diseases of mollusks — par- 

 ticularly oysters. — and Hutton, Sogandares- 

 Bernal, Eldred, Ingle, and Woodburn (1959) 

 reported on parasites and diseases of some of 

 the commercial shrimps. Certain general as- 

 pects of invertebrate diseases, such as immune 

 mechanisms, have been considered (Cantacu- 

 zene, 1923, 1928; Huff", 1940; Baer, 1944; Stein- 

 haus, 1949; Staiiber, 1961), and a few research 

 groups, such as Frederik B. Bang and his as- 

 sociates at The Johns Hopkins University, and 

 Albert K. Sparks and his co-workers at the 

 University of Washington, have been concerned 

 with comparative pathology of invertebrates 

 (Bang, 1956, 1961, 1962; Bang and Bang, 

 1962; Bang and Lemma, 1962; Levin and Bang, 

 1964; Rabin and Bang, 1964; Sparks and 

 Pauley, 1964; Pauley and Sparks, 1965). 



Much of our knowledge about diseases of 

 marine invertebrates concerns species of eco- 

 nomic importance, particularly the bivalve 

 molluscan and crustacean shellfish. This paper 

 is concerned only with the important diseases 

 of these two groups. We have attempted to 

 encompass as much literature as possible from 

 widely separated areas. Many diseases of ma- 

 rine invertebrates are inadequately character- 

 ized, and it is probable that others have not 

 even been recognized. Microbial pathogens that 

 have been implicated in mass mortalities in- 

 clude bacteria, fungi, and protozoans. Several 

 of the larger parasites have been found to be 



pathogenic under specific conditions. Not in- 

 cluded here are most of the parasites and dis- 

 eases of noncommercial species — those species 

 that may be of great significance in the cycles 

 of life in the sea, but which are not of sig- 

 nificant direct importance as food for humans. 

 Among the groups thus excluded are gastro- 

 pods and cephalopods, barnacles, copepods, and 

 most of the smaller crabs. Also excluded are 

 many diseases that have been incompletely de- 

 scribed in the scientific literature. 



A summarization of knowledge in any area 

 of research, however specialized in its scope, is 

 subjective and in some ways frustrating to 

 the reviewer; yet a consolidation of research 

 results can be useful, particularly to the non- 

 specialist. Much published information about 

 diseases of marine bivalve mollusks and crusta- 

 ceans has accumulated, aiul at least a repre- 

 sentative fraction of the available literature 

 has bpen considered in this paper. Preparation 

 of a bibliography of molluscan shellfish diseases 

 has been a continuing project of the BCF (Bu- 

 reau of Commercial Fisheries) Biological Lab- 

 oratory, Oxford, Md., for 6 years; this bibliog- 

 raphy, as well as standard bibliographic and 

 abstracting sources, has been u.sed in preparing 

 the manuscript. There is little representation 

 of the Russian literature — this may be in part 

 a reflection of the relative lack of emphasis 

 placed on shellfish in Russian fishery research, 

 as well as the limited availability of transla- 

 tions of Russian literature. Some of the older 

 European literature, particularly that on spe- 

 cific parasites of invertebrates, has not been 

 considered in this paper but is accessible 

 through references cited in more recent publi- 

 cations. Although necessarily limited in con- 

 tent, this review attempts to assess the state 

 of knowledge about the role of disease in two 

 major groups of commercial marine inverte- 

 brates. 



DISEASES OF BIVALVE MOLLUSCA 



Most of the commercial bivalve mollusks oc- 

 cur in shallow inshore waters, often inter- 

 tidally, where they are accessible to quanti- 

 tative evaluation and observation. Unusual 

 mortalities are more apparent here than in off- 

 shore populations. As a result, literature on 



336 



U.S. FISH AND WILDLIFE SERVICE 



