abundant in July; none are known to occur be- 

 fore July or after the first week in September, 

 and about the same length of breeding season is 

 found in the Beaufort, N.C., area. Gray (1942) 

 presented evidence for two spawnings per season. 

 The act of egg laying has not been studied in 

 minute detail, but Gray (1942) observed egg dep- 

 osition among captive females held in aquaria. 

 Completion of spawning was usually accom- 

 plished in a day but sometimes took as long as 3 

 days, depending on temperature. (Hyman (1920) 

 and others have dug ovigerous females from bur- 

 rows.) Freshly laid eggs were yellow or pale 

 orange in color, but the color changed with de- 

 velopment through a purplish-black to an ashy 

 gray color, at which stage the larvae emerged 

 (see also Hyman, 1920). Estimated egg counts on 

 a number of ovigerous females ranged from 10,000 

 to 300,000, depending on size of the individual. 

 Newly laid eggs measured about 0.09 mm. in di- 

 ameter but increased to about 0.27 mm. at the time 

 of hatching. Both Hyman (1920) and Gray 

 (1942) observed that the females entered water in 

 order to let the eggs hatch. Time of hatching ex- 

 tended from about 7:00 to 10:00 p.m., and the 

 hatching of an egg mass required slightly less 

 than an hour. 



The first zoeal stage of U. minax is the smallest 

 among our three species of TJca. The larval stages 

 are discussed in the remarks on U. pugilator. 



Uca minax is an omnivorous feeder but avoids 

 highly putrified debris (Gray, 1942). Teal (1958) 

 showed that fiddler crabs can subsist on a mixture 

 of sand, clay, bacteria, and fermented marsh 

 grass (natural staples in their diet), and he ob- 

 served U . minax kill and eat U. pugnax and U. 

 pugilator on several occasions. Contrary to the 

 findings of others, he observed (1959) that U. 

 minax can and does feed underwater. Miller 

 (1961) compared the mouthparts of U. minax to 

 those of the more specialized Carolinian Ucas. 

 He found that it prefers to feed in low areas of 

 the Spartina marshes well up in estuaries where 

 mud is fluid. 



In a search for factors that might limit U. 

 minax to its particular habitat, Teal (1958) 

 found that the temperatures experienced in nature 

 had no effect on survival but that the species could 

 live in fresh water for more than 3 weeks and, 

 when offered fresh and salt water, U. minax chose 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 

 763-049 O — 65 16 



to live in fresh water. When offered a choice of 

 mud or sand substrates, this species chose mud 

 either above or under water, but when competi- 

 tive species of Uca were present fewer burrows 

 were dug. Teal (1959) found that U. minax had 

 the lowest rate of oxygen consumption among a 

 number of marsh crabs investigated (U. pugnax 

 and pugilator, Sesarma cinereum and reticulatum, 

 Eurytium limosum, and Panopeus herbstii) which 

 is contrary to the argument of Ayers (1938) that 

 the more terrestrial species have relatively higher 

 rates of metabolism than do aquatic forms. Teal 

 (1959) and Vernberg (1959) further observed 

 that U. minax in all probability does not accli- 

 mate respiratory rate to changes in temperature. 

 Gray (1957) found gill area per gram of body 

 weight in U. minax lowest among East Coast Ucas, 

 Below 20° C, this species is inactive (Gray, 1942; 

 Teal, 1959). Gray found that U. minax overwin- 

 ters in burrows just below the frost line. 



Sexual display of the males among fiddler crabs 

 has been a subject of much study and is too com- 

 plex for complete review here. Crane (1943, 

 1944) dealt with this subject briefly for U. minax. 

 In display, the males rear back on the last two or 

 three walking legs so that the carapace is vertical. 

 The major cheliped is extended diagonally up to 

 about half of maximum extension. This position 

 may be held for minutes, then the cheliped may 

 be fully extended swiftly and smoothly, and fin- 

 ally brought back to the half-extended position 

 in a series of jerks. This movement may be re- 

 peated about four times rather slowly. The small 

 cheliped is moved asynchronously in similar mo- 

 tions. 



Uca pugnax (Smith). Mud fiddler 



Figures 209B, 210A 



Oelasimus pugnax Smith, 1870, p. 131, pi. 2. fig. 1, pi. 4, 

 figg. 2-2d. 



Uca pugnax: Rathbun, 1918b, p. 395, pi. 139.— Hay and Shore, 

 1918, p. 451, pi. 37, fig. 4. — Tashian and Vernberg, 1958, p. 89 

 ( rev. ) . 



Recognition characters. — Carapace subquadri- 

 lateral, approximately 1.5 to 1.75 times as wide 

 as long, widest behind outer orbital angles, very 

 convex anteroposteriorly, lower edge of front and 

 upper margin of orbit invisible in dorsal view, 

 smooth. A shallow H-shaped depression near cen- 

 ter of carapace, a pit on branchial region in line 

 with gastro-cardiac sulcus, and a pit behind mid- 



229 



