no. 3602 CRAYFISHES — HOBBS, HOLT, AND WALTON 9 



of C. branchiophila is within the gill chambers of the crayfish; (2) 

 Ankyrodrilus koronaeus (his species X) is primarily an inhabitant of 

 the chelipeds; (3) Pterodrilus alcicornus is randomly distributed over 

 the ventral surface of the crayfish; (4) C. fallax is essentially confined 

 to the basal segments of the pereiopods and antennae; (5) C. ingens 

 occurs principally upon the ventral surface of the abdomen and along 

 the cervical groove, but competes with C. fallax so that, when one 

 species is common upon a crayfish, the other is rare ; (6) Xg. instabilius 

 is found almost always on the chelipeds. Of the other species in- 

 cluded in this study, Bdellodrilus illuminatus is known beyond doubt 

 to be a gill-inhabiting form; it is assumed that the microhabitat of 

 A. legaeus is that of its congener and that these two species are allo- 

 patric; Xd. formosus, on the basis of our field experience, is a species 

 of the exterior surface of the branchiostegites of the crayfish; and 

 little or nothing can be said of the microhabitats of the remaining 

 species (C. heterognatha, C. philadelphica, and C. holostoma), though 

 we suspect that C. philadelphica and C holostoma may occupy es- 

 sentially the same microhabitats as C. fallax and C. ingens. 



Goodnight (1940, p. 65) and McManus (1960, pp. 424-427) have, 

 among others, considered the question of host specificity among the 

 branchiobdellids. Goodnight reviewed the host records presented by 

 previous workers and said, "In short, within the limits of the range 

 of any branchiobdellid any crayfish may serve as host." McManus 

 found it surprising that branchiobdellids should have the broad 

 ecological tolerances attributed to them and attempted to study this 

 problem in New York from an area where there are three species of 

 branchiobdellids and four of their crayfish hosts. He found very 

 few worms and no cocoons on Orconectes p. propinquus, confirmed by 

 experimental procedures that 0. immunis is an unsatisfactory host for 

 Cambarincola philadelphica and C. fallax (lumped together by him 

 as Cambarincola species), noted that all subadults and adults of 

 Cambarus robustus earned either worms or cocoons, and observed that 

 C. b. bartonii is very commonly infested. Lytle (pers. comm.) reports 

 a similar finding for branchiobdellids from central Pennsylvania. 



Populations 



The crayfishes.— No quantitative data on crayfish populations 

 in the area are available, but it is readily apparent that population 

 sizes vary tremendously from stream to stream and even from year to 

 year in corresponding seasons. Unfortunately, in this study observa- 

 tions were largely confined to the summer months, and most seasonal 

 fluctuations, if they occurred, might well have escaped detection. 

 Admittedly, in certain instances the fluctuations are more apparent 

 than real; for example, it is highly unlikely that there are fewer indi- 



