Genus Rhithropanopeus Rathbun, 1S98 



Rathbun, 1930a, p. 455.— Hemming, 1958b, p. 37. 



Rhithropanopeus harrisii (Gould) 



Figures 169, 183C 



Piliimnus harrisii Gould, 1841, p. 320. 



Rhithropanopeus harrisii: Hay and Shore, 1918, p. 441, pi. 

 35, fig. 5.— Rathbun, 1930a, p. 456. pi. 183, figs. 7-8 (rev.). 



Recognition characters. — Carapace subquad- 

 rate, approximately three-fourths as long as wide, 

 much less convex from side to side than from 

 front to back, sparsely pubescent toward antero- 

 lateral angles; protogastric regions with two 

 transverse lines of granules; a similar line from 

 one posterior lateral tooth to opposite one across 

 nasogastric region. Front almost straight, 

 slightly notched, and with margin transversely 

 grooved, appearing double when viewed from in 

 front. Postorbital angle and first anterolateral 

 tooth completely coalesced; first and second de- 

 veloped anterolateral teeth of about same size and 

 perhaps larger than last one. 



Chelipeds unequal and dissimilar; carpus not 

 grooved above and with a moderately developed 

 internal tooth; chelae indistinctly costate above. 

 Major chela with short immovable finger and 

 strongly curved dactyl. Minor chela with pro- 

 portionately longer immovable finger and long 

 straight dactyl. Walking legs long, slender, com- 

 pressed, and somewhat hairy. 



Measurements. — Carapace: male, length, 15 

 mm. ; width, 19 mm. 



Variations. — The chelipeds are nearly smooth 

 in old individuals, but in small specimens the 

 carpus is rough with lines and bunches of gran- 

 ules, the distal groove deep, the upper margin of 

 palm with two granulate ridges, and the upper 

 edge of the fingers granulate. 



Color. — Brownish above, paler below; fingers 

 light. 



Habitat.— In Chesapeake Bay, Ryan (1956) 

 found this species distributed primarily in the up- 

 per bay and in tributaries of the lower bay in 

 depths of to 5 fathoms. A similar distribution 

 has been found for upper Delaware Bay (Mc- 

 Dermott and Flower, 1953) and the tributaries 

 of the Neuse River estuary in North Carolina. 

 Ryan collected specimens in waters ranging from 

 fresh to 18.6 °/ 0o . The places from which the 

 form was taken always afforded some kind 

 of shelter — oyster bars, living and decaying 



Figure 169. — Rhithropanopeus harrisii (Gould). Frontal 

 aspect of body viewed from above, 3 mm. indicated. 



vegetation, old cans, and other debris. Bousfield 

 (1955) found larvae of the species in water from 

 4 to no higher than 28.5 % salinity. Surface 

 to 20 fathoms. 



Type locality. — Cambridge Marshes and 

 Charles River, Mass. 



Known range. — The original range of this spe- 

 cies was in fresh to estuarine waters from New 

 Brunswick, Canada, to Veracruz, Mexico; north- 

 east Brazil. The species has been introduced on 

 the west coast of the United States and in parts of 

 Europe. 



Remarks. — Connolly (1925) stated that four 

 zoeal stages and one megalops stage comprise the 

 larval and postlarval development of this species. 

 These conclusions were based on study of plank- 

 ton taken from the Miramichi River estuary, New 

 Brunswick, Canada, in August. Chamberlain 

 (1962) confirmed and supplemented Connolly's 

 account with eggs taken from Chesapeake Bay 

 and cultured in the laboratory. Duration of larval 

 stages was twice as long when zoeae were fed cope- 

 pod nauplii and algae as when fed nauplii alone. 

 In an array of salinities and temperatures, devel- 

 opment was found to proceed best at 6 to 10 % 

 salinity. Developmental time increased with de- 

 creasing temperature, Developmental times of 

 larvae in nature were found to be in agreement 

 with results of laboratory culturing at similar 

 salinities and temperatures. Mortality rates for 

 larvae in nature were found to be lower than ex- 

 pected. A relatively high rate was postulated for 

 the megalops or early crab stages. Presence of 

 adult crabs in fresh water was deemed a result of 

 migration after larval stages are complete. Hood 



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