no. 3621 CRAYFISH FROM ALABAMA CAVES — HOBBS 9 



None of the students of crayfishes, to my knowledge, have ques- 

 tioned the primitiveness of the Limosus Section of the genus Orconec- 

 tes, as originally pointed out by Ortmann (1905a, p. 108), and none 

 since have denied that that assemblage embraces or has close affinities 

 with the troglobitic species ranging from Indiana to Alabama. (There 

 is disagreement concerning the taxonomic treatment of the epigean 

 and spelean members of the section (Rhoades, 1944; Hobbs, 1948; 

 Creaser, 1962), and Creaser has taken issue with the generic nomen- 

 clature that was proposed by Hobbs (1942), but this is of little 

 consequence in the context of the present discussion.) 



A comparison of the troglobitic members of the genus Orconectes 

 with members of the genus Procambarus demonstrates that these 

 troglobites possess a distinctly advanced first pleopod of the male 

 that is approached most closely in the genus Procambarus by the spe- 

 cies of the Mexicanus Group. Only one species of this group, P. acantho- 

 phorus Villalobos (1948, p. 175), can be claimed on the basis of the 

 pleopod to be more generalized, for it is the only member of the group 

 in which the first pleopod terminates in three rather than two parts 

 (a small cephalic process is present.) 



Were the first pleopods considered alone in assessing the primi- 

 tiveness of the Mexicanus Group among its relatives in the genus 

 Procambarus, one would be almost forced to conclude that the group 

 is an advanced one within the genus (see Hobbs, 1962, p. 276). There 

 is, however, additional evidence that the group is indeed an advanced 

 segment of it: (1) the males are provided with ischiopodal hooks 

 only on the third pereiopods; (2) the majority of the species have 

 comparatively long narrow areolae, usually denoting a broad ecological 

 tolerance; (3) most members have few spines, often associated with 

 a secondary burrowing (advanced) habit; (4) there is a unique sternal 

 modification (here designated the proannular plate) immediately 

 anterior to the annulus ventralis of the females that is encountered 

 elsewhere in the family only in the members of the Cubensis Group; 

 and (5) the comparatively long, slender chelipeds of the males most 

 definitely are not of a primitive type. If the members of the Mexicanus 

 Group thus are to be considered as close relatives of the primitive 

 Orconectes, one might well conclude that Orconectes has been derived 

 not from the more primitive but from an advanced segment of the 

 genus Procambarus. One must not conclude, however, that it was 

 from the Mexicanus Section of the genus that the primitive Orconectes 

 was derived, for a few primitive characteristics are retained in the 

 troglobitic Orconectes, some that do not exist in the Mexicanus stock: 

 (1) multiple cervical spines in most of them; (2) a rudimentary caudal 

 process on the first pleopod of the male in 0. pellucidus australis; 

 (3) hooks on the ischia of the third and fourth pereiopods; and (4) 



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