Figure 186. — Speoearcinus carolinenHs Stimpson. Type 

 female in dorsal view (after Rathbun, 1933). 



Family Pinnotheridae 



Carapace often somewhat membranous. An- 

 terolateral margins entire or very slightly den- 

 tate. Front, orbits, and eyestalks very small, cor- 

 nea often rudimentary. Buccal cavity usually 

 wide, often semicircular in outline. Merus of third 

 maxilliped never quadrate, and never with palp 

 distinctly at anterointernal angle; ischium small, 

 absent, or fused with merus and directed obliquely 

 inward (Rathbun, 1918b). 



Small crabs living as commensals or parasites 

 in bivalve mollusks, ascidians, worm tubes, and on 

 or in echinoderms. Free living or migratory stages 

 are occasionally taken in open water. 



KEY TO GENERA IN THE CAROLINAS 



a. Dactyls of walking legs simple, acute. 



b. Third walking leg little, if any, longer than other 

 legs. 



e. Carapace suborbicular and somewhat membranous 

 in mature female, flattened and firm in hard stage 

 male and female buccal mass subquadrate 



Pinnotheres (p. 203). 

 cc. Carapace oval, flattened, and rather firm ; buccal 



mass subtriangular Parapinnixa (p. 208). 



bb. Third walking leg longer and stronger than others, 



often considerably so Pinnixa (p. 210). 



aa. Dactyls of first, second, and third walking legs bifur- 

 cate DissodaetyUis (p. 209). 



Subfamily Pinnotherinae 



Carapace usually not markedly transverse. 

 Ischium of external maxillipeds either rudimen- 

 tary or indistinguishably fused with merus to 

 form single piece, usually oblique, occasionally 

 nearly transverse; palp not so large as merus- 

 ischium (Rathbun, 1918b). 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 



Genus Pinnotheres Bosc [1801 or 1802] 



Rathbun, 1918b, p. 62. — Hemming, 1958b, p. 36. 



KEY TO SPECIES IN THE CAROLINAS 



Hard-stage males and females 



a. Carapace with a striking pattern of light spots on dark 



background of pubescence maculatus (p. 206). 



aa. No striking color pattern ostreum (p. 203). 



Posthard females (and male maculatus) 



a. Carapace nearly naked ostreum (p. 203). 



aa. Carapace covered with a short deciduous pubescence 



maculatus (p. 206). 



Pinnotheres ostreum Say. Oyster crab 

 Figures 187, 188, 189 



Pinnotheres ostreum Say, 1817, p. 67, pi. 4, fig. 5. — Rathbun, 

 1918b, p. 66, text-fig. 30 : pi. 15, figs. 3-6 (rev.). — Hay and Shore, 

 1918, p. 443, pi. 35, fig. 9. 



Pinnotheres depressum Say, 1817, p. 68. 



Pinnotheres depressus: Rathbun, 191Sb, p. 79, pi. 17, figs. 1-2 

 (rev.). 



Recognition characters. — Mature female : Cara- 

 pace subcircular in outline; surface glabrous for 

 most part, smooth, shining, membranous, yielding 

 to touch, convex from front to back and with a 

 broad, shallow, longitudinal depression at each 

 side of cardiac and gastric areas. Lateral margins 

 thick and bluntly rounded; posterior margin 

 broad. Front rounded, slightly produced, cover- 

 ing and concealing eyes. Orbits small, subcircular, 

 anteriorly placed. Antennule large ; antenna small, 

 flagellum not so long as diameter of orbit. Buccal 

 mass roughly quadrangular in outline but bent 

 into broad crescentic arch, short anteroposteri- 



Figuee 1ST .—Pinnotheres ostreum Say. Mature female 

 in dorsal view, 5 mm. indicated. 



203 



