WILLIAMS: MUD CRAB. PARTITION INTO SIX SPECIES 



yellowish to cream or off-white; fingers brown with 

 white on tips and edges of teeth, shades of light brown 

 to tan on inner surface of fingers. Walking legs var- 

 iegated as carapace. (From color slide by D. L. Felder; 

 see also Reames and Williams 1983.) Third max- 

 illipeds of males with red spot near base of inner sur- 

 face of ischium, females lacking spot (Heard 1982). 



Known range. — The known geographic range of this 

 species, represented by the material listed above, is 

 shallow intertidal and subtidal waters of the northern 

 Gulf of Mexico: Key West, Fla (1 doubtful lot); Lee 

 County, Fla., to Corpus Christi, Tex. 



Remarks. — See general discussion below. 



Key to species ofPanopeus in the 

 "herbstii complex." 



Characters of major chelae refer to original or fully 

 regenerated state. 



la. Major chela with cusps of teeth on fixed 

 finger not reaching above imaginary 

 straight line drawn between tip and angle at 

 juncture of finger with anterior margin of 

 palm (= length fixed finger) 2 



lb. Major chela with cusps of teeth near 

 midlength of fixed finger reaching above an 

 imaginary straight line drawn between tip 

 and angle at juncture of finger with anterior 

 margin of palm (= length fixed finger) .... 3 



2a. Coalesced anterolateral teeth 1-2 sepa- 

 rated by shallow rounded notch, 2 broader 

 than but not so prominent as 1 ; 4 curved for- 

 ward as much as 3; 5 much smaller than 4, 

 acute and hooked forward; palm with dis- 

 tance between crest at base of dactyl and tip 

 of cusp lateral to base of dactyl 0.7 or less 

 length of fixed finger P. herbstii 



2b. Coalesced anterolateral teeth 1-2 sepa- 

 rated by deep rounded notch, adjacent 

 slopes of each about equal, 2 nearly as prom- 

 inent as 1; 4 not curved forward as much as 

 3; 5 much smaller than 4, usually projecting 

 straight anterolaterally, sometimes slightly 

 hooked; distance between crest of palm and 

 tip of cusp lateral to base of dactyl 0.8 or 

 more length of fixed finger P. simpsoni 



3a. Major chela with cusps of teeth in "molar 

 area" of fixed finger very broad, often 

 coalesced and worn, their external faces 

 often flared or bowed outward. ... P. lacustris 



3b. Major chela with cusps of teeth in "molar 

 area" of fixed finger somewhat enlarged but 

 separated from each other, in line with axis 

 of finger, not bowed outward 4 



4a. Anterolateral teeth 3-5 definitely swept for- 

 ward, acute, anterior margins noticeably 

 concave (especially 3-4) .... P. meridionalis 



4b. Anterolateral teeth 3-4 curved but not 

 noticeably swept forward, anterior margin 

 of at least 3 rectangular and often round- 

 ed 5 



5a. Anterolateral teeth more or less prominent, 

 arc drawn along tips of first 4 teeth diverg- 

 ing laterally from arc drawn along bases of 

 notches between teeth P. austrobesus 



5b. Anterolateral teeth usually rounded, not 

 prominent, arc drawn along tips of first 4 

 teeth converging laterally with arc drawn 

 along bases of notches between teeth. 

 P. obesus 



DISCUSSION 



The Panopeus herbstii, s.l., complex of mud crabs 

 occurring in intertidal and shallow littoral regions of 

 the western Atlantic, especially in estuaries and 

 lagoons, is a discouragingly close-knit group of 

 species with few clear-cut characters. Before the 

 diagnoses offered above were developed, the extent 

 of the differences was unknown (but indicated by 

 several authors), although ground work for making 

 such determinations was laid by finding evidence for 

 specific differences in morphometry and ecology be- 

 tween local populations of P. obesus and P. simpsoni in 

 the northern Gulf of Mexico (Reames and Williams 

 1983) and comparably strong evidence for specific 

 differences in hemocyanins and ecology among P. 

 herbstii, s.s.,P lacustris, P. obesus, andP simpsoni in 

 the southeastern United States (Sullivan et al. 1983). 

 The question then was: Were these differences 

 paralleled by morphological evidence that applied to 

 the whole complex throughout the geographic range? 

 Answer was sought by reevaluation of a large series of 

 specimens, including statistical analysis of certain 

 measurements and study of the first male pleopods 

 at high magnification. 



The first pair of pleopods in males of many 

 brachyurans exhibit characters that are useful in dis- 

 tinguishing species, but study of these structures in 

 this series by light microscopy and scanning electron 

 microscopy shows no consistent differences. 



Carapace length and width were recorded for P. 



877 



