Figure 15>4. — Pinnixa chaetopterana Stinipson. A, male 

 in dorsal view ; B, chela of male in frontal view ; C, 

 chela of female in frontal view ; 5 mm. indicated. 



oval gape when closed with tips of fingers meet- 

 ing. Hand of female relatively smaller; immova- 

 ble finger with tooth somewhat beyond middle 

 followed by an irregularly dentate, raised, cutting 

 edge terminating in a blunt tip; dactyl with a 

 small basal tooth, longer than in male, fingers 

 agape proximal to cutting portion when closed 

 with tips crossing each other. First and second 

 pairs of walking legs slender, propodi with distal 

 V-shaped row of spinules on lower border ; dactyls 

 with one or more short rows of spinules. Third 

 pair longer and much stouter, conspicuously pu- 

 bescent, and with inferoposterior margins of is- 

 chium, merus, and propodus dentate; fourth pair 

 like third but smaller, with minute spinules on 

 dactyls. 



Male abdomen with sixth segment slightly con- 

 stricted laterally, at middle; telson semicircular. 



Measurements. — Carapace : male, length, 6 mm., 

 width, 14 mm.; female, length, 6 mm., width, 

 11 mm. 



Variations. — Wass (1955) pointed out, that two 

 forms of this species occur on the northern Gulf 

 of Mexico coast, a larger and smaller form. 



Color. — Nearly white, but usually much ob- 

 scured by brown or blackish hairs and by dirt 

 collected in them; eggs bluish (various authors). 



Habitat. — The large form of this crab lives com- 

 mensally with the worms Chaetopterus varioped- 

 atus and Amphitrite ornata, and is seldom found 

 outside their tubes. The small form lives in the 

 upper portion of Callianassa burrows on the 



northern Gulf coast (Wass, 1955). Intertidal to 

 8.5 fathoms. 



Type locality. — Charleston Harbor, S.C., on 

 muddy or clayey shores in tubes of Chaetopterus 

 variopedatus [ = perga/nentaceus]. 



Known range.- — Wellfleet, Mass., to South Caro- 

 lina; Punta Rassa, Fla., to Galveston, Tex.; Rio 

 de Janeiro, and Villa Bella, Sao Sebastiao, Brazil. 



Remarks. — Ovigerous females have been re- 

 ported from Beaufort, N.C., between April (Gray, 

 1961) and late October (Enders, 1905), from 

 Florida in October (Wass, 1955) and February 

 (Gray, 1961), and from southern Massachusetts 

 in July and August (Pearse, 1913; Rathbun, 

 1918b). Otherwise they are known from South 

 Carolina in February. Faxon (1879) and Hyman 

 (1924a) described the first zoeal stage. 



Some habits of this crab were observed by 

 Pearse (1913) at Woods Hole, Mass. The species 

 is strongly thigmotactic. Crabs placed on sand 

 in an aquarium usually buried themselves, but 

 soon explored the surface and entered and re- 

 mained in glass tubes left lying on the sand. In 

 experiments, crabs found a buried, artificial "Cha- 

 etopterus tube" by accident. Adult crabs could 

 enter or leave this tube. The crabs moved either 

 forward or sideways on sand. The third walking 

 leg was the chief locomotor organ, but in tubes the 

 crabs braced themselves with all the legs. 



Crabs placed in standing water in an artificial 

 worm tube were able to exist for 8 days before 

 leaving the tube for better aerated water. The 

 crabs' respiratory currents were feeble and incon- 

 stant in direction and force. Crabs were usually 

 fouled with encrusting organisms and they took 

 no trouble to clean their bodies except for mouth 

 parts, eyes, and antennae. They fed by extending 

 the fringed external maxillipeds and sweeping 

 them toward the mouth, filtering small particles 

 from the water, then cleaning the fringe with 

 other mouth parts. 



Gray (1961, see also account for Polyonyx gib- 

 besi) described Pinnixa chaetopterana. as primar- 

 ily a mud crab and a facultative commensal of 

 Chaetopterus. He found that the crabs readily 

 enter and leave the tubes of the host, and if di- 

 ameter of the parchment chimney of the worm 

 tube is too small, the crab bites a hole at the base 

 of the chimney to make an entrance or exit. 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 



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