has a relatively wide abdomen reaching the coxae 

 of the legs in most cases (carapace width, 3.6- 

 8.9 mm.). Stage V is the adult female described 

 above. 



The posthard stages are passed through rapidly. 

 In Delaware Bay by mid-July, 62 percent of 

 females have developed from the overwintering 

 stage to maturity. By mid-August, 95 percent are 

 mature and more than half are ovigerous; thus, 

 P. ostrevm reaches maturity within its first year. 

 Males live 1 year or less, but females continue to 

 grow after they have hatched their first batch of 

 eggs and may live to an age of 2 or 3 years, though 

 many probably die after they have hatched their 

 eggs in the second summer. In the second or third 

 year, females may become ovigerous as early as 

 mid-June, and ovigerous yearlings may occur as 

 late as mid-October. Farther south the breeding 

 season is more extended, and ovigerous females 

 have been collected near Ocracoke, N.C., as early 

 as mid-April. 



Ovigerous females measuring 9.4 and 10.8 mm. 

 in width carried 7,957 and 9,456 eggs respectively. 

 It is not known how long a female carries eggs, 

 but it is believed to be 3 to 5 weeks. The females 

 produce only one batch of eggs the first year but 

 in a second or third year may produce twice. 



Except for the. brief free-swimming periods in 

 the invasive hard stages, the crabs lead a parasitic 

 existence. Stauber (1945) and Christensen and 

 McDermott (1958) both found that the crab feeds 

 on food filtered from water by the host by picking 

 food strings from the margins of the gills with its 

 chelipeds. The crab also will catch newly formed 

 mucus-food masses with its walking legs and 

 then reach beneath the abdomen with its chelipeds, 

 comb the legs, and pass the food on to the mouth. 

 The method of feeding for young crabs not on the 

 gills is unknown, but they may filter food with 

 the mouth parts. Posthard stages are found only 

 on the gills, indicating that feeding on the food- 

 laden mucus alone can insure adequate food for 

 rapid growth and egg production. Growth of 

 females is positively correlated with size of host 

 and is probably related to food supply and 

 amount of water pumping by the host. 



The ordinary feeding activities are harmful to 

 the host ( Stauber, 1945), particularly causing gill 

 erosion of two types, local erosion of one or more 

 demibranchs, and an extensive shortening of denii- 



branchs from the anterior end of gills to a point 

 ventral to the adductor muscle. Christensen and 

 McDermott (1958) noted that this erosion is a 

 progressive process and nearly all infested oysters 

 show some gill damage, some few older oysters 

 having hardly any gill tissue left. Usually, how- 

 ever, only presence of a mature crab over a long 

 time will noticeably affect growth of an oyster in 

 normal environmental circumstances. 



Pinnotheres tnaculatus Say. Mussel crab 

 Figure 190 



Pinnotheres maculatum Say, ISIS, p. 450. 



Pinnotheres tnaculatus: Rathbun, 191Sb, p. 74, text-figs. 35-36, 

 pi. 17, figs. 3-6 (rev.).— Hay and Shore, 1918, p. 443, pi. 35, 

 fig. 10. 



Recognition characters. — Mature female: cara- 

 pace suborbicular, somewhat broader than long, 

 thick and firm but not hard, convex, smooth; sur- 

 face uneven, covered with a short, dense, decidu- 

 ous tomentum. Gastrocardiac area higher than, 

 and separated by depressions from, branchio- 

 hepatic area. Front slightly advanced, approxi- 

 mately one-fifth width of carapace, subtruncate 

 in dorsal view, slightly bilobed. Orbits small, 

 subcircular, eyes spherical. Antenna longer than 

 width of orbit; antennule large, obliquely trans- 

 verse. Buccal mass roughly quadrangular, cres- 

 centic, much broader than long; ischium and 

 merus of external maxilliped united; propodus 

 larger than carpus; dactyl narrow, curved, spatu- 

 late, attached near middle of propodus, and 

 reaching to near extremity of propodus. 



Chelipeds moderately stout, articles subcylin- 

 drical and more or less pubescent; carpus elon- 

 gate; palm thick, blunt edged, increasing in size 

 distally ; fingers stout, fitting closely together with 

 tips hooking past each other; immovable finger 

 nearly horizontal ; dactyl with tooth near base fit- 

 ting into sinus with tooth at either side on immov- 

 able finger. Walking legs slender, hairy above 

 and below; second pair longest, shorter than che- 

 lipeds; first three dactyls falcate, shorter than 

 propodi ; last leg shortest, turned forward and 

 upward, with long dactyl equaling propodus. 



Abdomen large, extending to bases of legs. 



Measurements. — Carapace: length, 13.7 mm.: 

 width, 14.3 mm. 



Color. — Obscure brown. 



Recognition characters. — Mature male: Cara- 

 pace flat, subcircular, diameter about half as great 



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FISH AND WILDLIFE SERVICE 



