WILLIAMS: MUD CRAB, PARTITION INTO SIX SPECIES 



she placed most of those specimens which she 

 examined in or near form obesa. 



A sixth species, represented by a very small sample, 

 is intermediate between the two groups discussed 

 above. Its superficial resemblance to P. simpsoni in 

 narrowness of carapace, surface granulation, and 

 lack of a basal red spot on the inner surface of the 

 ischium of the third maxilliped in females is offset by 

 prominence of the molar area aligned with the axis of 

 the fixed finger of the major chela. 



The species thus are separable on the basis of car- 

 apace width-length relationships, with considerable 

 overlap (Table 1, Fig. 9), which are reinforced by a 

 second character, the shape and dentition of the 

 fixed finger of the major chela. The somewhat 

 obscured width-length relationships are presented 

 as linear regressions for samples of five of the species 

 in Table 2 . These were tested with the ANC OVA pro- 

 cedure, but sample size for the sixth, P. meridionalis, 

 was too small to allow comparable treatment. AtP = 

 0.05, there is a significant difference in linear regres- 

 sion of samples of the groups (species) (F= 34.4647* 

 with 4, 252 df). The hypothesis that the slopes for this 

 regression are equal is rejected (F = 24.6288* with 4, 

 244 df) as is the hypothesis that the intercepts are 

 equal (F = 31.5588* with 4, 244 df). The Newman- 

 Keuls MRT procedure is able to separate these five 

 species into only four significantly different but over- 

 lapping groups. The test thus has limited utility for 

 discrimination, merely restating what was known from 

 visual inspection, and emphasizing the fact that other 

 characters must be used in combination with carapace 

 dimensions in making species determinations. 



The ranges of these species fit known zoo- 

 geographic distribution patterns for many littoral 

 decapod crustaceans (Perez Farfante 1969; Williams 

 1965). The tropical species, P. lacustris, is wide- 

 spread from Bermuda and southern Florida through 

 the Caribbean Sea to the region of Cabo Frio, Brazil, 

 and flanked by apparent cognates to the north and 

 south. Panopeus herbstii, s.s., is associated with oys- 

 ter beds along the Atlantic coast of the United States 

 from Boston Harbor to southeastern Florida; the 

 closely related P. simpsoni occupies the same habitat 

 in the Gulf of Mexico, and a similar species in 

 Uruguay, P. meridionalis, may occupy a comparable 

 niche. Panopeus obesus, associated mainly with salt 

 marshes, is distributed in the Carolinian Province 

 from Beaufort, N.C., to northeastern Florida, and 

 from western Florida to northeastern Mexico. Pan- 

 opeus austrobesus seems to be a southern counter- 

 part of the latter, ranging from near Cabo Frio, Brazil, 

 southward, although its precise habitat cannot be 

 determined from the collection data at hand. 



ACKNOWLEDGMENTS 



Several people helped to bring this study to comple- 

 tion. J. L. Russo gave statistical advice. B. B. Col- 

 lette, D. L. Felder, R B. Manning, R. C. Reames, andB. 

 Sullivan gave critical comments on the manuscript. 

 W. R. Brown, Susan Braden, and Mary Jacques 

 Mann operated the USNM scanning electron micro- 

 scope. Keiko H. Moore made the illustrations, Ruth 

 E. Gibbons gave technical assistance, and Virginia R. 

 Thomas entered the text on a word processor. 



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879 



