Hara's Cave Amphipod

Stygobromus harai

MATERIAL EXAMINED.—CALIFORNIA. Tuolumne Co.: Pinnacle Point Cave, holotype female (USNM 142784) and 4 paratypes (JRH), P. Hara, 27 Nov. 1971; mine tunnel near Pinnacle Point Cave, 3 paratypes (USNM 142785), P. Hara, 27 Nov. 1971.

DIAGNOSIS.—A medium-sized cavernicolous species, closely related to S. gradyi and S. grahami but differing from these two species as follows: smaller size of sexually mature females; fewer apical spines on inner plate of maxilliped; inner margin of posterior angle of gnathopodal propod 1 with mostly unforked spine teeth; gnathopodal propod 2 of male proportionately a little larger than 2nd propod of female, with double row of 13 spine teeth on palm; coxal plates of gnathopod 2 and pereopods 3 and 4 not as deep; ramus of uropod 3 with 3 apical spines; and proportionately longer telson which is about one-third longer than broad. Largest females, 7.5 mm; largest males, 7.0 mm.

FEMALE.—Antenna 1: 40 to 45 percent as long as body, 40 to 45 percent longer than antenna 2; primary flagellum with 16 segments. Antenna 2: peduncular segments with fewer spines and setae than S. grahami; flagellum with 7 segments. Mandibles like those of S. gradyi (with fewer spines in spine row than S. grahami). Maxilla 1: inner plate with 10 or 11 plumose setae apically; palp with 4 spines and 2 setae apically and subapically. Maxilla 2: inner plate with oblique row of 13 plumose setae on inner margin. Maxilliped: inner plate with 3 or 4 bladelike spines (some with small bristles), 5 plumose spines and 3 setae apically and row of plumose spines (or heavy setae) on inner margin; outer plate like that of S. grahami. Lower lip with small inner lobes.

Gnathopodal Propod 1: Palm rather long, convex, armed with double row of 8 or 9 spine teeth; posterior angle with 6 spine teeth on outside, 7 smaller spine teeth on inside; posterior margin with 1 seta submarginally just below defining angle; medial setae singly inserted. Coxal plate of gnathopod 1 longer than broad, with 4 marginal setae. Gnathopodal propod 2 nearly twice the size of 1st propod; palm long, oblique, convex distally, concave proximally, armed with double row of 10 spine teeth plus 3 additional spine teeth on outside; posterior angle with 1 long, curved spine tooth and 5 setae on outside, 1 shorter spine tooth on inside; posterior margin with 1 set of setae; medial setae mostly singly inserted; dactyl long, curved, nail not reaching to defining angle. Coxal plates of gnathopod 2 and pereopod 3 about as broad as long, with 5 marginal setae each; coxal plate of pereopod 4 about as broad as long, about one-third as long as segment 2, with 7 marginal setae. Pereopod 6 equal in length or slightly longer than pereopod 7, 40 to 50 percent as long as body, 30 to 35 percent longer than pereopod 5. Bases of pereopods 5–7 a little broader proximally than distally; posterior margins slightly convex; distoposterior lobes small, distinct, rounded. Dactyls of pereopods 6 and 7 about one-third the length of corresponding propods. Coxal gills present on pereopods 2–6. Brood plates of mature females small and narrow.

Pleonal Plates: Posterior margins slightly convex; posterior corners small, distinct, rounded; ventral margin of plate 2 with 4 spines, that of plate 3 with 5 spines. Uropod 1: inner and outer rami equal in length, about two-thirds the length of peduncle; inner ramus with 8 or 9 spines; outer ramus with 9 or 10 spines; peduncle with 10 or 11 spines. Uropod 2: inner ramus about 20 percent longer than outer ramus and peduncle, armed with 10 or 11 spines; outer ramus with 8 or 9 spines; peduncle with 3 or 4 spines. Uropod 3: ramus about 40 percent as long as peduncle, with 3 apical spines. Telson subrectangular, about one-third longer than broad; apical margin with small notch; apical lobes with 5 or 6 spines each.

MALE.—Differing from the female in the structure of gnathopodal propod 2 and uropod 1 as follows: Gnathopodal propod 2 proportionately a little larger; palm with double row of 13 spine teeth; posterior angle with 1 long spine tooth and 5 setae on outside, 3 shorter spine teeth on inside; posterior margin with 2 sets of setae; dactyl nail rather short. Peduncular process of uropod 1 not finely serrate as in S. gradyi.

TYPE-LOCALITY.—Pinnacle Point Cave, about 10 miles east of Valecito, Tuolumne County, California. The type-locality is located about 5 miles east-southeast of Crystal Palace Cave and on the south side of the Stanislaus River. This cave, like many others in the Mother Lode cave region, is developed in marble or limestone of the Calaveras formation and was described by Halliday (1962). The type-series, consisting of three males and two females, was collected from a small lake in the cave.

DISTRIBUTION AND ECOLOGY.—This species is known from its type-locality and a nearby mine tunnel. The November collection from the mine tunnel contained one male and two females. One of these females (6.0 mm long) had two embryos in the brood pouch. A third embryo was found loose in the collecting vial. A single female (7.0 mm long) from the type-locality had setose brood plates but was not ovigerous.

ETYMOLOGY.—This species is named in honor of its collector, Paul Hara.

Stygobromus harai, commonly called Hara's cave amphipod, is a troglomorphic species of amphipod in family Crangonyctidae. It is endemic to Tuolumne County, California in the United States.