Libinia emarginata Leach. Spider crab 



Figures 231, 233H 



Libinia emarginata Leach, 1815, p. 130, pi. 108. — Hay and 

 Shore, 1918, p. 456, pi. 38, fig. 6. — Rathbun, 1925, p. 311, text- 

 figs. 103-104 ; pis. 110-113 (rev.). 



Recognition characters. — Carapace orbicular, 

 about one-sixth longer than wide, spinose and 

 tuberculate, with dense covering of short hairs. 

 Larger spines arranged as follows: median row 

 of about nine extending from near base of ros- 

 trum to posterior border consisting of four gas- 

 tric, one genital, two cardiac, and two intestinal ; 

 lateral marginal spines five on each side; two 

 subhepatic spines; two or four spines above pos- 

 terior margin, aside from median spine, and about 

 four dorsal branchial spines; spiniform tuber- 

 cles scattered about among larger spines. Gastric 

 region marked off by a deep groove. Rostrum 

 slightly depressed, emarginate or bifid at tip; a 

 median groove between eyes. Orbits with promi- 

 nent preorbital spine, two spines beneath on basal 

 article of antenna; one fissure above and one be- 

 neath. 



Chelipeds equal, larger in male; hands granu- 

 late ; fingers smooth, evenly denticulate, and about 

 half as long as hand. Walking legs long, hairy, 

 unarmed, often unequal and asymmetrical (result, 

 perhaps, of injury and subsequent regeneration). 



Measurements. — Carapace: male, length, 103 

 mm., width including spine, 94 mm.; female, 

 length, 62 mm., width, 58 mm. 



l'ii. i be 231. — Libinia emarginata Leach. Male in dorsal 

 view, legs <>f left side not shown, 20 nun. Indicated. 



Variations. — The number of median spines in 

 the gastric region is subject to some variation in 

 size and number. 



Color. — A brownish or dirty yellow. 



Habitat. — Found on almost any kind of bot- 

 tom ; shore to 27, occasionally 68, fathoms. 



Type locality. — Unknown. 



Known range. — Windsor, Nova Scotia, to west- 

 ern Gulf of Mexico. 



Remarks. — Hildebrand (1954) reported this 

 species as the most common large spider crab in 

 the western Gulf of Mexico. It was most common 

 in July, at which time ovigerous females were ob- 

 served. Another ovigerous female was taken in 

 February. (Elsewhere ovigerous females are 

 known from New Jersey in August (U.S. Na- 

 tional Museum records).) Hildebrand also ob- 

 served juveniles riding in the bell of scyphozoan 

 Stomolophus meleagris, a habit noted by others 

 for the young of L. dubia. 



The young of L. emarginata and L. dubia are 

 difficult to distinguish. Wass (1955) pointed out 

 useful distinguishing marks. "The rostrum of 

 L. dubkt is much longer, forming a V; the cara- 

 pace is not so wide, and there is but one spine on 

 the intestinal region . . . whereas L. emarginata 

 has two.'' 



Gray (1957) compared gill area in this sluggish 

 species with that of other common littoral crabs in 

 the Carolinas and found that it had the smallest 

 gill area per gram body weight of any studied. 



Libinia dubia H. Milne Edwards. Spider crab 



Figures 232, 2330 



Libinia dubia H. Milne Edwards, 1834, p. 300, pi. 146i«, fig. 2. — 

 Hay and Shore, 1918, p. 456, pi. 38, fig. 5.— Rathbun, 1925, p. 313, 

 text-figs. 105-106; pis. 114-115; pi. 122, fig. 1 (rev.). 



Recognition characters. — Similar in general 

 characters to L. emarginata but with more pyri- 

 f orm carapace and fewer spines ; median row with 

 but six spines, two gastric, one genital, two car- 

 diac, and one intestinal; preorbital, subhepatic, 

 and lateral spines stronger than in L. emarginata, 

 but spiniform tubercles few or wanting altogether. 

 Rostrum slightly longer and more definitely bifid 

 than in L. emarginata. Anterolateral angle of 

 buccal frame armed with a spine. 



Measurements.— Carapace : male, length, 102 

 mm.; width including spines, 82 mm. Most indi- 

 viduals smaller. 



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