548 



FRESH-WATER BIOLOGY 



Embryos from 85 to 108 M long. 



Echinorhynchus thecatus Linton 1892. 



Body cylindrical , slightly curved; proboscis curved also. 

 Female n to 26 mm. long; width 0.51 to 0.89, anteriorly 0.8 

 to 1.4 mm. in maximum, 0.52 to i mm. posteriorly. Male 7 

 to 12 mm. long; width 0.39 to 0.69 anteriorly, 0.59 to 0.95 in 

 maximum, 0.37 to 0.75 posteriorly. Hooks in 24 to 31 trans- 

 verse and 1 2 longitudinal rows surrounded by prominent collars. 

 Embryos 85 to 108 /z long by 1 8 to 22 n broad. (Graybill.) 



In alimentary canal and body cavity of Micropterus dolo- 

 mieu, Ambloplites rupestris, Amia calva, and Roccus lineatus. 

 Great Lakes and eastern waters. 



FIG. 850. Echinorhynchus thecatus. a, hooks from ventral side of 

 proboscis near base; b, hook from ventral, i.e., concave side of probos- 

 cis; c, hooks from dorsal, i.e., convex side of proboscis. X 150. (After 

 Linton.) 



1 8 (17) Embryos from 115 to 165 /* long. . Echinorhynchus sahelini Linkins. 



Male 7 to 9 mm. long, 0.82 to 1.27 mm. broad. Fe- 

 male 10 to 17 mm. long, 1.2 to 1.6 mm. wide. Proboscis 

 armed with 26 circular rows of 8 hooks each. Hooks 

 alternate in adjacent rows. Basal hooks 39 to 50/1 

 long; hooks in middle and anterior regions 44 to 68 n 

 long, those with basal processes 83 ju long. Embryos 

 115 to 165 fj, long by 20 to 25 /z wide. 



From lake trout; Lake Michigan. 



FIG. 851. Echinorhynchus sahelini. Optical section through 

 anterior region of body. X 60. (After Linkins.) 



19 (14) Spines on body at some point at least, usually at anterior end. . 20 



20 (23) Body tapers regularly towards both ends. Proboscis in line with 



axis of body. Posterior limit of spines alike on dorsal and 

 ventral surfaces 21 



21 (22) Cement glands tubular Polymorphus Liihe 1911. 



Fine spines on skin of anterior body. Just behind the limit of these spines a conspicuous 

 annular constriction. Type species P. minutus (Goeze) fiom various European water birds. 

 At least one species yet undescribed from North American Anseriformes. 



22 (21) Cement glands irregularly ovoid. (Males and some females or 



young specimens.) Filicollis Liihe 1911. 



Compare number 37 in this key. 



The males, the young females and even some adult females of certain species have a proboscis 

 that departs only slightly from the usual type, being a little enlarged but not conspicuously 



