SECTION IV 

 KEY TO NORTH AMERICAN SURFACE-LIVING SPECIES OF ASELLUS 



The following key is of use only for adult male specimens; as indicated 

 in the text above, it is the males which in Asellus provide the diagnos- 

 tic characters for the species separation. Females cannot be identified 

 at present. In the key, the terms mesial process, lateral process, 

 caudal process, ventral groove, and cannula refer to structures at the 

 tip of the endopod of the second pleopod. All drawings of the first and 

 second pleopods, unless contraindicated, are of right pleopods. With 

 respect to the surface of these, ventral=anterior, and dorsal=posterior. 

 All principal distinguishing characters have been used in compiling the 

 key, and are illustrated in the accompanying figures (no direct refer- 

 ence may be made to such characters in the final part of the couplet for 

 each species). In certain cases, to aid identification some quantitative 

 data are given in tabular form. 



1 Palm of propodus of peraeopod 1 lacking triangular process near 

 midpoint, but with 3-5 teeth- like spines variously arranged 

 (Fig. lOA) . Pleopod 1 distinctly longer than pleopod 2, dis- 

 tal segment with numerous long plumose setae (Fig. lOB) . Pleo- 

 pod 2 with mesial and caudal processes not developed, but lat- 

 eral process large, projecting beyond cannula, and distally 

 recurved (Figs lOD, E, llA-E); endopod shape and relative pro- 

 portions of segments as in Fig. IOC. Both exopod and endopod 

 of uropod longer than peduncle (Fig. lOF, G) : A. ocoidentdlis 

 Palm of propodus of peraeopod 1 usually (not always) with both 

 a large triangular process near midpoint and some teeth-like 

 spines variously arranged. Pleopod 1 either longer than 

 pleopod 2 and distal segment with numerous long plumose 

 setae, or shorter to subequal in length to pleopod 2 and 

 lacking distal plumose setae. Lateral process of pleopod 2 

 either absent or developed in conjunction with mesial process 

 (i. e. not as shown in Figs lOD, E, llA-H); endopod shape 

 and relative proportions of segments more or less dissimilar 

 to those shown in Fig. IOC. Exopod of uropod typically 

 shorter than peduncle, endopod usually subequal in length 

 to peduncle (but sometimes longer) 2 



2(1) Pleopod 1 usually subequal in length to pleopod 2 or distinctly 

 shorter, distal segment subovate to subrectangular without 

 long plumose setae on distal margin but with few to numerous 

 short simple setae. Pleopod 2 with prominent cannula, 

 often wide, never hidden ventral ly by lateral or mesial 



processes 3 



Pleopod 1 usually distinctly longer than pleopod 2, distal 

 segment usually subovate, often curved outward, and with 

 few to numerous long plumose setae on distal margin. Pleopod 

 2 with small, narrow cannula sometimes hidden ventrally by 

 lateral or mesial processes 10 



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