no. 3602 CRAYFISHES — HOBBS, HOLT, AND WALTON 47 



Entocytkerid associates include Dn. ileata at stations 3, 5, 7, 24, 44, 

 64; Dn. scalis at 7, 38, 44, 82, 101, 103; and E. kanawhaensis at 44. 



Branchiobdellid associates include B. illuminatus at stations 5, 44; 

 C. branchiophila at 24; C. heterognatha and P. alcicornus at 3, 5, 24, 64; 

 C. holostoma at 7; C. ingens at 5, 64; C. philadelphica at 3, 5, 24, 44; and 

 Xg. instabilius at 3, 5, 7, 24, 44, and 64. 



The Branchiobdellids 



The epizoites that compose the clitellate order BranchiobdeUida 

 are annelids with leechlike suckers and a short body of 15 segments 

 of which the first four form a "head." Segmentation is obscured by 

 coalescence in the head and also posteriorly in the formation of the 

 posterior sucker, so that usually only the trunk segments are num- 

 bered; e.g., the anterior nephridia are said to open on segment III, 

 but actually this is segment VII. The conventional system of desig- 

 nating the first trunk segment as I will be followed here. The body 

 is cylindrical (terete) in most species, but members of three genera 

 (Ankyrodrilus, Xironodrilus, and Xironogiton) are variously dorso- 

 ventrally flattened (depressed) in body form. 



The trunk segments, marked internally by distinct muscular 

 septa anterior to the sucker, are further subdivided into annuli, 

 normally only two, of which the anteriormost (prosomite) is longer 

 and often greater in diameter than the posterior annulus (metasomite) . 

 Some branchiobdellids possess dorsal projections of various types on 

 the prosomites of some trunk segments (fig. 20). 



A prostomium, common among the annelids, is absent in the 

 branchiobdellids. The mouth is surrounded by a peristomium (the 

 first head segment) that is set off by a sulcus and may be entire (not 

 divided into lobes or provided with tentacles) or variously lobed or 

 tentaculate, but most often the peristomium forms dorsal and ventral 

 lips. The buccal cavity of all branchiobdellids, presumably in the 

 second head segment, is armed with sclerotized "jaws": one dorsal, 

 one ventral. These jaws are usually provided with denticles ("teeth" : 

 figs. 12c, /). The number of teeth is often expressed by a "dental 

 formula" in which the teeth of the upper jaw are enumerated first. 



The reproductive systems have been found to provide the most 

 reliable taxonomic characters. The components of these systems 

 may best be imderstood by reference to figures 126, 14a, and 15a. 

 Testes, not patent in mature animals, are found in segments V and 

 VI, ovaries in segment VII. Spermatogenic cells and spermatozoa 

 fill the coelomic spaces of the testicular segments and the spermatozoa 

 are conveyed to the outside by a series of ducts, beginning in the male 

 funnels (f), which are the ental ends of the efferent ducts. The 



