8 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 123 



Entocytherinae are not parasitic on their crayfish hosts, there seem 

 to be few reasons why one might expect host specificity to have 

 developed. Nevertheless, there are a few species that have been 

 found only on one host. This apparent specificity is more probably 

 related to the the habitat of the crayfish than to other factors, for 

 in most of these associations a burrowing crayfish is involved, either 

 C. carolinus or C. d. diogenes. Of the nine species of the genus Asceto- 

 cythere (see Hobbs and Hart, 1966), five of them have been found only 

 on C. carolinus; both species of the genus Plectocythere are restricted 

 to the same crayfish; and the three species of the genus Geocythere 

 (see Hart, 1959, 1965) and the monotypic Rhadinocythere (see Hart, 

 1965) have been found only on C. d. diogenes. In the Mountain 

 Lake region, As. asceta and Dt. chalaza share a single host, C. carolinus. 



The branchiobdellids. — The branchiobdellids are epizoites known 

 from several holarctic freshwater crustaceans, principally decapods of 

 the family Astacidae, but they have been recorded from freshwater 

 crabs (Hobbs and Villalobos, 1958, p. 395; Holt, 1964, p. 2), fresh- 

 water shrimp (Liang, 1963, pp. 569, 570), and a cave isopod (Holt, 

 1963, p. 99). All attach to the exterior surface of the host by means 

 of a posterior sucker and move from place to place on the host's 

 body in a leechlike fashion, using the peristomium as an anterior 

 sucker. All of the branchiobdellids considered here are from crayfishes. 



Most species of branchiobdellids are not found in all parts of the 

 streams of a drainage system in which they occur. There are, pre- 

 sumably, ecological factors regulating such distributional patterns; 

 but in general it is not known what these factors are, though Berry 

 and Holt (1959, p. 7) showed a difference in the temperature re- 

 sponses of Xironogiton instabilius and Xironodrilus formosus, which 

 suggests that an intolerance of high temperatures may operate in 

 confining Xg. instabilius to the colder streams of higher elevations. 



The occurrence of several species of branchiobdellids (as many as 

 six) on the same host animal has raised the question as to whether or 

 not a particular species is confined to a specific part of the body of 

 the host. Holt (1954, p. 170) first called attention to the problem 

 presented by the possible existence of microhabitats for branchiobdel- 

 lids on the crayfish hosts. McManus (1960, p. 422) studied three 

 species of branchiobdellids, Xg. instabilius, Cambarincola philadelphica, 

 and C. fallax, all of which occur in the Mountain Lake area) from Fall 

 and Cascadilla Creeks in New York, and his observations are in 

 accord with those of Brown (1961, p. 25), who has studied, from 

 Sinking Creek, the microhabitats of 6 of the 12 species of branchiobdel- 

 lids that occur in the Mountain Lake area. Though a more rigorous 

 control of his statistical procedures would have been desirable, there 

 is no reason to doubt his general conclusions: (1) the microhabitat 



