ecdysis duration in II. pugnax. Surprisingly, at 

 some temperature between 15° and 22° C. pro- 

 ecdysis fails to proceed normally, though these 

 animals experience much lower temperatures 

 throughout their range. It was suggested that 

 the northern limits of the species are influenced 

 by the inability of larvae to molt in cold water; 

 hence, adults cannot appear there. 



Crane (1943) gave a detailed description of the 

 display and breeding relationships for this spe- 

 cies. Display of males starts with the body ele- 

 vated moderately high and both chelae held well 

 off the ground and flexed in front of the mouth. 

 Both chelipeds are extended obliquely upward, 

 then the major claw is returned downward in a 

 jerk or a series of jerks with no pause between 

 extension and flexion. The fingers usually remain 

 nearly closed, and a complete cycle of movement 

 usually requires about 2 seconds. (Movement of 

 the small chela is not described.) At times males 

 will exhibit a series of bobbings or "curtseys," 

 especially when displaying to females. Pearse 

 (1914) and others considered these activities to 

 be courtship display. 



Other activities which have received much at- 

 tention in experiments are rhythmic cycles. 

 Brown and his coworkers (Brown and Sandeen, 

 1948; Brown and Webb, 1948, 1949; Brown, 

 Webb, Bennett, and Sandeen, 1954) showed that 

 fiddler crabs (among them U. pugnax) exhibit 

 temperature-independent, diurnal, rhythmical 

 color changes. These rhythms may be altered, or 

 delayed, by lowering temperature for a time, or 

 by, altering the period or time of illumination. 

 They further demonstrated that possibly two cen- 

 ters of rhythmicity exist in these crabs, each capa- 

 ble of having its rhythm altered independently of 

 the other, and with one center influencing the 

 other. Brown, Fingerman, Sandeen, and Webb 

 (1953) demonstrated that amplitude of diurnal 

 cycles under constant conditions increased to a 

 maximum in 2 weeks. Superimposed on diurnal 

 cycles are tidal rhythms which persist in phase 

 witli native local conditions under constant labor- 

 atory conditions. Oxygen consumption reflects 

 these cycles as well as a lunar cycle (Brown, Ben- 

 nett, and Webb, 1954; Brown, Fingerman, and 

 ITines, 1954; Brown, Webb, Bennett, and San- 

 deen, 1955). Bennett, Shriner, and Brown (1957) 

 found that degree of spontaneous locomotor ac- 



tivity is also related to tidal cycles although the 

 rhythm persists only about a week under constant 

 conditions. 



Primarily because of the tremendous asym- 

 metry in chelipeds of male fiddler crabs, Uca be- 

 came an object of studies on relative growth. (In 

 some of these papers no clear species designation 

 was made.) In fiddler crabs [Uca pugnax\ the 

 percentage weight of the chela alters throughout 

 life from 2 percent (the value retained by the 

 female) to 65 percent (Huxley, 1927). In the re- 

 lated larger species, U . minax, since allometric 

 growth continues longer, the chela may weigh 

 over three-fourths of the remainder of the body 

 (77 percent ) . Increasing relative size of the chela 

 is associated with an increasing asymmetry of the 

 central nervous system. Thus, such animais have 

 no fixed form, for the proportions of parts are 

 changing throughout postlarval life. On this 

 basis, Huxley challenged Morgan's (1923) state- 

 ment that females with intermediate width abdo- 

 mens (subject also to allometric growth, Huxley, 

 1924) were actually intersexual female types. 

 Tazelaar (1933) explored the subtleties of relative 

 growth in U. pugnax in detail, finding that walk- 

 ing legs near the great chela and near the wide 

 abdomen of females also reflect relative growth 

 influences. 



Uca pugilator (Bosc, [1801 or 1802]). Sand fiddler 



Figures 209C ; 210 C, D ; 211 



Ocypoda pugilator Bose, [1801 or 1802], p. 197. 

 Uca pugilator: Rathbun, 1918b, p. 400, pi. 141 ; pi. 160, fig. 2 

 (rer.).— Hay and Shore, 1918, p. 452, pi. 37, fig. 2. 



Recognition characters. — Carapace subquadri- 

 lateral, up to 1.5 times as wide as long, widest be- 

 hind outer orbital angles, very convex, smooth; a 

 shallow H -shaped depression near center of cara- 

 pace and a narrow, flattened shelf behind orbit. 

 Lateral margin strongly curved outward behind 

 orbit, continued backward and inward as a low, 

 well-defined ridge across entire frontoorbital 

 width. Front more than one-third of frontoorbital 

 width, broadly rounded below. Orbits large, open, 

 upper margin slightly sinuous, lower margin den- 

 tate. Eyestalks long, slender. Antennule and 

 antenna small. Merus of second maxilliped with 

 150 to 200 spoon-tipped hairs arranged in about 10 

 rows on inner side. 



Chelipeds in male very unequal, in females 

 equal and small. Merus of large chela with short, 



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