Mackin, 1957; Woodburn et al., 1957; Hiitton, 

 Sogandares-Bernal. Eldred, Ingle, and Wood- 

 burn, 1959; and Kruse, 1959a, 1959b). Aldrich 

 (1965) found the same cestode larvae in Pe- 

 naeus azteciis and P. setiferus from the Texas 

 coast. The adult worm was identified from the 

 Atlantic stingray Dasyotis sahina LeSueur. An- 

 other trypanorhynch larva, unidentified, was 

 seen by Ward (1962) in great numbers in the 

 abdominal muscles, gills, and pericardium of 

 the white shrimp from the Gulf of Mexico. 



Trypanorhynch larvae have been found in 

 commercial shrimps from other parts of the 

 world. Yamaguti (1934) reported larvae, prob- 

 ably Tetrarhynchus rubromaculatus Diesing, in 

 Penaeopsis sp. from Japan. Heldt (1949) took 

 a larval cestode resembling Eutetrarhynchus 

 riificollis (Eysenhardt) from Penaeus trisulca- 

 tus Leach from the North African coast. 



Larval nematodes of the genus C.oiitracaeciim 

 were found in Florida shrimps by Woodburn et 

 al. (1957), Hutton, Sogandares-Bernal, Eldred, 

 Ingle, and Woodburn (1959), and Kruse 

 (1959b). Margolis and Butler (1954) observed 

 adult nematodes, C. aduncum, in a single speci- 

 men of northern pink shrimp Pa))dalus borealis 

 Kroyer from British Columbia, Canada. 



Diseases Caused b>' Parasitic Crustaceans 



Epicaridean isopods are well-known para- 

 sites of Crustacea, and several genera occur on 

 shrimps. Baer (1951), for example, stated that 

 the epicaridean Hemiarthrus ubdominalis 

 (Kroyer) had been recovered from 20 species 

 of shrimps belonging to the genera Pandalus 

 and Spirontocaris. Joseph Uzmann (personal 

 communication, Jan. 31, 1967) has found H. 

 abdominalis on northern pink shrimp from the 

 Gulf of Maine. The parasite has also been re- 

 ported on P. borealis from Greenland (Horsted 

 and Smidt, 1956) but not from Norway or 

 England (Dahl, 1949; Allen, 1966). 



Eicketts and Calvin (1962) described the 

 occurrence of the bopyrid isopod Argeia puqet- 

 tensis, which caused unilateral protuberances 

 of the carapace of the black-tailed shrimp, 

 Crago nigrictiuda (Stimpson), from the Pacific 

 coast of the United States. Infestation was esti- 

 mated at 3 to 5 percent. Japanese "red prawns," 

 Pevaeopsis akayebi Rathbun, are frequently 

 (up to 70 percent) infested with another bopy- 



rid Epipomcon japo))icns Thielemann. Hiraiwa 

 and Sato (1939) found the gonads of parasit- 

 ized individuals reduced, or in some males, com- 

 pletely atrophied. Presence of the branchial 

 parasite Bopyrus squillarum on the shrimp 

 Leander serrifer causes suppression of the ova- 

 ries and the breeding characters of the pleo- 

 pods (Yoshida, 1952). 



Several rhizocephalans have been reported as 

 parasites of shrimps. Potts (1912) described 

 Mycetomorphavayicouveroisis from Crago com- 

 mutiis Rathbun, and Caiman (1898) described 

 Sylon hippolytes from the dock shrimp, Panda- 

 lus danae Stimpson, both from Puget Sound, 

 Wash. 



DISEASES AS A POSSIBLE CAUSE 

 OF MASS MORTALITIES 



Many physical, chemical, and biological vari- 

 ables contribute directly or indirectly to mor- 

 talities of commercially valuable marine inver- 

 tebrates. Various environmental factors and 

 some of their eff'ects have been discussed by 

 Dexter (1944), Brongersma-Sanders (1957), 

 Coe (1957), Mackin (1961), Dickie and Medcof 

 (1963), Medcof and Bourne (1964), and Mer- 

 rill and Posgay (1964). It seems clear that the 

 actual cause of death in many mass mortalities 

 is often undetermined, even after exhaustive 

 studies such as those of Orton (1924a, 1924b), 

 who studied oyster mortalities in England in 

 1920-21, and Roughley (1926). who examined 

 oyster mortalities in Australia in 1924-25. 



Disease has often been suspected as a cause 

 of mortalities, but the actual disease agent 

 often has proved to be elusive. Hirsch (1921), 

 Dollfus (1923), and Korringa (1952a) reported 

 major mortalities of sea mussels, probably due 

 to a contagious disease, in the period 1900-19. 

 The mortalities reached a peak in 1914-16. Sick 

 mussels lost their byssal attachment, mantles 

 were retracted, meats were thin, and adductor 

 muscles were weak. Histological and bacterio- 

 logical examinations wei'e inconclusive. Soon 

 thereafter — 1919-23 — catastrophic mortalities 

 of European oysters occurred in western Eu- 

 rope. Deaths began in 1919 in Mar Piccolo, 

 near Taranto, Italy (Cerruti, 1941), and 

 quickly spread to England and other European 

 countries. Orton (1924a) suspected, but was 



DISEASES OF THE MARINE BIVALVE MOLLUSCA AND CRUSTACEA 



361 



