salinity and temperature. Eggs were maintained 

 in salinities of 12.5, 20.1, 26.5, and 31.1 %„ and 

 all larvae hatched as first stage zoeae. Succeeding 

 stages showed higher percentages of survival un- 

 der different conditions, with shortest develop- 

 ment time in the highest salinity. The lowest 

 salinity tested did not permit development to be 

 completed. In addition, low temperature affected 

 duration of all larval stages and mortality of 

 some stages. Larval development was completed 

 to first crab in 48-52 days at 20° C, in 18-28 

 days at 30° C. From data, the effects of salinity 

 and temperature on mortality of larval stages 

 were projected by statistical methods over a wide 

 range of combinations. The hypothesis is pre- 

 sented that the effect of temperature on successive 

 larval stages limits the productive spawning 

 period. Low temperatures favor the spring brood 

 of larvae [in these latitudes], prolonging larval 

 development until warmer water produces favor- 

 able conditions for the megalops stage. Larvae 

 hatched in fall are not so favored and mortality 

 in late zoeal and megalops stages would be high. 



In a study of the relationship of habitat to oxy- 

 gen consumption by estuarine crabs, Ayers ( 1938 ) 

 found P. herbstii to be intermediate in a scale of 

 partial adaptation of the respiratory mechanisms 

 to life in air. Teal (1959) found this species 

 active on Georgia marshes when the tide was high 

 or the sky cloudy. When the marsh was exposed, 

 it was found in burrows, usually near the top, in 

 air or water. Among various marsh crabs studied 

 (see remarks, TJca minax) only P. herbstii was 

 active at temperatures below 12° C. Respiration 

 in this crab was most affected by reduced oxygen 

 pressure among species tested, showing a rate re- 

 duction of 90 percent at 4 mm. Hg. 



Menzel and Nichy (1958) found that P. herb- 

 stii and Miiiijijir iiierceiiiiria are the only xanthids 

 large enough to kill significant numbers of adult 

 oysters. McDermott (I960), studying predatory 

 activities of xanthid crabs on oyster beds in New 

 Jersey, found thai /'. herbstii destroyed 1- and 2- 

 year-old oysters at a rate of 0.15 oysters per end) 

 per day. The crab also preyed actively on oyster 

 spat as well as barnacles (B alarms improvisus) . 

 He concluded that P. herbstii is potentially the 

 most destructive of the five species of mud crabs 

 occurring on New Jersey oyster beds. 



Panopeus occidentalis Saussure 



Figures 181, 183N 



Panopeus occidentalis Saussure, 1857, p. 502. — Rathbun. 

 1930a, p. 348, text-fig. 55; pi. 161. figs. 1-3 (rev.). 



Recognition characters. — Similar to Panopeus 

 herbstii, but differing in having more convex cara- 

 pace, especially in gastric region; front narrow, 

 advanced; second anterolateral tooth usually nar- 

 rower and separated by deeper sinus from first 

 tooth, third to fifth teeth thicker, more prominent 

 and widely separated, third one blunt, forming 

 almost a right angle at tip; abdomen of male 

 wider, sides of penultimate segment not parallel, 

 narrowed toward proximal end. 



Carpus of chelipeds with groove parallel to 

 distal margin, sometimes rugose; dark color of 

 immovable finger not continued on palm. Walking 

 legs somewhat longer and more slender. 



Measurements. — Carapace: male, length, 23 

 mm. ; width, 33 mm. Smaller than P. herbstii. 



Variations. — There is considerable variation 

 even in a single lot of specimens. The carapace 

 may be smooth and shining, or with light, granu- 

 late, transverse lines; the second anterolateral 

 tooth may be small, subacute, and similar to the 

 first rather than broadly rounded and large; the 

 female abdomen may have sides of the sixth seg- 

 ment parallel instead of converging slightly to- 

 ward the proximal end. Variations in teeth of the 

 anterolateral border were noted in 12 percent of 

 females studied by de Oliveira (1940). In these 

 the first, second, and third teeth of one side were 

 depressed, giving the impression of but one sinu- 

 ous tooth while those of the other side were 

 normal. 



This species, like P. herbstii. has 'been divided 

 into two environmental forms (typical and ser- 

 rate), and both occur in the Carolinas (Rathbun, 

 1930a). 



Cot or. — Carapace dull yellow spotted with 

 brown and red; legs yellow with brown macula- 

 tions and speckles on chelipeds; walking legs with 

 brown or rose streaks. De Oliveira (1940) gave 

 color of the species in Brazil as: carapace dark 

 yellow with red blotches or chocolate varying in 

 tone; legs same color but spotted with reticulated 

 points, points of lingers chocolate to almost black ; 

 body yellow ventrally, legs yellow to grayish: 

 some rare specimens completely yellow. 



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FISH AND WILDLIFE SERVICE 



