PARASITIC ROUNDWORMS 



547 



9 (2) Proboscis long. Numerous irregular circles of about six hooks each. 



Tanaorhamphus Ward. 



The extreme length of the proboscis and the large number of hooks 

 serve to contrast this with the previous closely related genus. Hooks 

 in the anterior row are not conspicuously larger than those following. 

 The cement gland has 16 nuclei. 



Only species known. 



Tanaorhamphus longirostris (Van Cleave) 1913. 



Body robust, posterior end flexed slightly ventrad. Females 

 average 6.2 mm. long, and 0.63 mm. in maximum breadth. Males 

 average 4 mm. long, and 0.47 mm. in maximum breadth. Proboscis 

 cylindrical with slight constriction one-third distance from base to 

 outer end, bent ventrad 60 degrees. Hooks in about 20 circular 

 rows of six to ten hooks each. Anterior hooks 54 fj, long, successive 

 hooks gradually smaller until within a few rows of the base where 

 they become abruptly smaller; basal hooks 16 n long. Embryos 

 oval 27 /j. long by 8 to io/z broad. 



In intestine of hickory shad from Illinois River; not abundant but 

 probably most frequent in summer and wanting in January to April. 



FIG. 849. Tanaorhamphus longirostris. Proboscis, X 75; embroyos, X 230. 

 (After Van Cleave.) 



10 (i) In hypoderm many small nuclei, not conspicuous externally. . . n 

 The proboscis sac has a double muscular wall. 



11 (36) Proboscis and neck simple, without bulbous enlargement even in 



fully developed specimens 12 



12 (27) Hooks in each circular row all alike; no contrast between different 



sides of proboscis 13 



13 (24) Proboscis sheath attached at posterior end of proboscis 14 



14 (19) Body of parasite entirely free from spines at all points 15 



15 (16) Retinacula emerge from proboscis sheath at blind posterior end 



which contains ganglion. Acanthocephalus Koelreuter 1771. 

 In marine and fresh-water fishes and Amphibia, larvae in Isopoda. 



Representative North American species. 



Acanthocephalus ranae (Schrank) 1788. 



Body elongate, club-shaped, largest near neck. Proboscis short, cylindrical. Twelve rows 

 each with 6 or 7 hooks which are 60, 70, 80 and 50 ju long. Embryos 1 10 n long by 13 yn broad. 

 This European species has been identified by Van Cleave who showed that it is apparently 

 rare in this country. 



From intestine of Diemyctylus viridescens taken near Baltimore, Maryland. 



16 (15) Retinacula emerge from lateral walls of proboscis sheath; ganglion 



distinctly anterior to blind posterior end of sheath. 



Echinorhynchus Zoega 1776 . . 17 



Neck wanting or very short; proboscis long, cylindrical, bent ventrad. Hooks numerous, 

 much alike throughout except that roots grow shorter and disappear in later rows. 



In marine and fresh-water fishes. 



Nearly every new species described from this continent has been assigned to this genus, 

 many of them erroneously. Several good species in North America. Abundant in whitefish 

 and lake trout from the Great Lakes. 



