do not enter the water to search for or capture 

 food. 



The crabs have to go into the water at intervals 

 to moisten the gills, and the young do this more 

 frequently than adults. When undisturbed, the 

 individuals do not actually enter water but will 

 stop a few inches from the waterline with one side 

 presented to the water, the legs of the other side 

 anchored in sand, and wait for a wave to wash 

 over them after which they return to the higher 

 parts of the beach. If disturbed, the crabs will 

 run into the water, then leave it as soon as possi- 

 ble. These crabs do not swim but walk on the bot- 

 tom or are rolled about by waves. The crabs can 

 survive for a limited time if forced to remain 

 submerged. 



Locomotion is accomplished by all eight walk- 

 ing legs. Usually the crabs walk sideways or 

 obliquely. If hotly pursued, the crabs will run in 

 another manner, holding the last pair of legs clear 

 of the ground. Usually the crabs walk or run 

 toward the side with the small chela. This crab 

 can also walk forward, or sometimes approach 

 food by walking slowly backward. 



The eyes of 0. quadrat a are so large and promi- 

 nent that it seems as if the crab can see exception- 

 ally well. Experiment has shown that the eyes are 

 primarily sensitive to large changes in intensity of 

 light. The crabs do not tend to avoid strong light, 

 but try to hide if lights are suddenly shut off or if 

 an object on the beach is suddenly moved. The 

 eyes apparently aid in the search for food, but 

 actual detection of food is by taste or smell. 



There is no evidence that 0. quadrat a can hear, 

 though a well-developed stridulating ridge is 

 borne on the large chela. No one has reported 

 observing this crab in the act of stridulating. 



Cowles (1908) noticed that the ghost crab ex- 

 hibits color changes. The crabs are generally dark 

 in subdued light and in direct sunlight if tem- 

 perature is not above 35° C. Above 35° C, the 

 crabs are light colored regardless of light inten- 

 sity. In absence of light, the crabs are light col- 

 ored regardless of temperature. 



The general relationship of habitat to oxygen 

 consumption and general activity among certain 

 decapods has been a subject of study by Ayers 

 (1938), Pearse (1929), Vernberg (1956), and 

 Gray (1957) in the Beaufort, N.C., area. In all 

 these studies, O. quadrata was of prime interest 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 



because of its terrestrial adaptation combined 

 with great activity. Of all the crabs studied in 

 this geographic area, the ghost crab possesses the 

 highest rate of oxygen consumption both for the 

 whole animal and for gill tissue alone. This is 

 more striking when it is emphasized that O. qua- 

 drata has a reduced number of gills (though it 

 does have accessory respiratory tissues in the gill 

 cavity) and the gill area per gram of weight in 

 this species is by far the lowest among 16 species 

 studied in near-shore, intertidal, and above-tide 

 zones. 



Flemister and Flemister (1951) and Flemister 

 (1958) have shown that when 0. quadrata is con- 

 fined in water, oxygen consumption is elevated, 

 but elevated least when chloride ion concentration 

 of the water equals that of the blood. Lower or 

 higher ion concentration of the water raises the 

 respiration rate. They demonstrated that the ani- 

 mals normally have blood hypotonic to sea water. 

 In sea water containing less than 120 or more 

 than 160 millimoles of chloride per liter, the in- 

 ternal concentration is not maintained but tends 

 to rise or fall depending on which end of this 

 range the animal experiences. The antennal gland, 

 aided by the gill membranes, functions in regula- 

 tion of internal chloride ion concentration. 



Genus Uca Leach, 1814 



Rathbun, 1918b, p. 374. — Monod, 1956, p. 399. 



KEY TO SPECIES IN THE CAROLINAS 



a. Large cheliped of male with oblique tubereulate ridge 

 on inner surface of palm extending upward from lower 

 margin. 



b. A prominent transverse depression behind orbit ; leg 

 joints red on large cheliped ; color dark, usually gray- 

 ish toward front margin minax (p. 227). 



bb. Without prominent transverse depression behind 

 orbit ; leg joints not red ; color dark, often with blue 



on front pugnax (p. 229). 



aa. Large cheliped of male without oblique tubereulate 

 ridge on inner surface of palm extending upward from 

 lower margin pugilator (p. 232). 



Uca minax (Le Conte). Red-jointed fiddler; brackish 



water fiddler 



Figures 209A, 210B 



Gelasimus mitmx Le Conte, 1855, p. 403. 

 Uca minax: Rathbun. 1918b, p. 389, pi. 137 (rev.). — Hay and 

 Shore, 1918, p. 451, pi. 37, fig. 3. 



Recognition characters. — Carapace subquadri- 

 lateral, approximately 1.3 times as wide as long, 

 widest behind outer orbital angles, convex in both 



227 



