Stygobromus lacicolus Holsinger 1974

Stygobromus lacicolus

Stygobromus hubbsi Shoemaker.—Frantz and Cordone, 1966: 7 (in part).

MATERIAL EXAMINED.—All material from Lake Tahoe at the indicated locations and depths. NEVADA. Douglas Co.: Cave Rock (215–501 ft), holotype male (USNM 142786), T. C. Frantz et al., 17 July 1962; Logan Shoals (1165 ft), 5 paratypes (USNM 142787), T. C. Frantz and A. J. Cordone, 16 Aug. 1962; El Dorado Co.: Homewood to Rubicon Bay (18–197 ft), 1 paratype (USNM 142789), Cordone and Frantz, 30 May 1962; Sugar Pine Point (480 ft), 1 paratype (USNM 142790), Frantz, Curran, and Saake, 18 July 1962. CALIFORNIA. Placer Co.: Tahoe City area (392 ft), 3 paratypes (USNM 142788), Frantz, Curran, and Saake, 24 July 1962.

DIAGNOSIS.—A medium-sized, deep-lake dwelling species, occuring sympatrically with S. tahoensis but differing from that species in gnathopodal propod 1 of the male which has a longer palm and more spine teeth, gnathopodal propod 2 of both sexes which has a longer palm and is broader proximally (strongly resembling S. wengerorum), deeper coxal plates of pereopods 3 and 4, broader bases of pereopods 5–7, fewer spines and setae on pleonal plates 2 and 3, fewer spines on uropods 1 and 2, smaller peduncular process (with serrate apex) of uropod 1 of the male, proportionately longer ramus of uropod 3, and proportionately longer telson with more apical spines. Largest female, 6.0 mm; largest males, 5.5 mm.

MALE.—Antenna 1, 40 to 45 percent as long as body, about 40 percent longer than antenna 2; primary flagellum with 13 segments. Antenna 2, flagellum with 6 segments. Mouthparts similar to S. tahoensis except maxilliped differing slightly as follows: inner plate with 3 serrate spines, 2 bladelike spines, and several setae apically; outer plate with 1 bladelike spine, 1 serrate spine, and 3 setae apically. Gnathopodal propod 1: palm long, convex, armed with double row of 9 or 10 spine teeth; posterior angle with 3 spine teeth on outside, 5 shorter spine teeth on inside; posterior margin about half the length of palm, without setae; medial setae singly inserted; dactyl nail rather long. Coxal plate of gnathopod 1 longer than broad, with 2 marginal setae. Gnathopodal propod 2: nearly twice the size of 1st propod; palm long, oblique, convex distally, concave proximally, armed with double row of 12 spine teeth plus 2 additional spine teeth on outside; posterior angle with 1 long spine tooth and 3 setae on outside, 2 shorter spine teeth on inside; posterior margin short, with 1 set of setae just below posterior angle; medial setae mostly singly inserted; dactyl rather long, nail comparatively short. Coxal plates of gnathopod 2 and pereopod 3 longer than broad, with 3 marginal setae each; coxal plate of pereopod 4 rather deep, as broad as long, reaching about half the length of segment 2, with 5 marginal setae. Pereopod 6 a little longer than pereopod 7, 45 to 50 percent as long as body, 20 percent longer than pereopod 5. Bases of pereopods 5–7 broader proximally than distally; posterior margins convex; distoposterior lobes distinct, broadly rounded. Dactyls of pereopods 6 and 7 relatively long, about one-third the length of corresponding propods. Coxal gills on pereopods 2–6.

Pleonal Plates: Posterior margins straight to slightly convex; posterior corners rounded, distinct; ventral margins of plates 2 and 3 with 3 spines each. Uropod 1: inner ramus slightly longer than outer ramus, a little shorter than peduncle, armed with 10 spines; outer ramus with 10 spines; peduncle with 10 spines and small process with tiny apical serrations. Uropod 2: inner ramus about one-fourth longer than outer ramus and peduncle, armed with 9 or 10 spines; outer ramus with 7 or 8 spines; peduncle with 5 spines. Uropod 3: ramus about one-half the length of peduncle, with 4 or 5 apical spines. Telson more than one-third longer than broad; apical margin with small rounded notch; apical lobes with 6 or 7 spines each.

FEMALE.—Known only from a single, partly broken specimen but apparently generally similar to male.

TYPE-LOCALITY.—Lake Tahoe at Cave Rock (depth = 215 to 501 ft), Douglas County, Nevada.

DISTRIBUTION AND ECOLOGY.—This species is known only from Lake Tahoe, where it was collected during the previously mentioned limnological survey by Frantz and Cordone in the early 1960s. Of the 16 samples of Stygobromus studied from Lake Tahoe, 5 contained specimens of S. lacicolus; 3 of the 5 contained only this species and 2 had both this species and S. tahoensis. Of these two species, S. lacicolus appears to be far less abundant in the lake, as the five samples, representing the months of May, July, and August, contained only 11 specimens. Of these 11 specimens, 8 were males, 2 were juveniles and 1 was a female. The association of Stygobromus with Lake Tahoe is discussed in more detail under the description of S. tahoensis.

ETYMOLOGY.—The specific name is from the Latin Lacus (lake) and colo (to inhabit).