Stygobromus nanus Holsinger 1978

Stygobromus nanus

Apocrangonyx species B.—Holsinger, 1969a:28.

Apocrangonyx sp.—Holsinger, Baroody, and Culver, 1976:22.

MATERIAL EXAMINED.—WEST VIRGINIA. Pocahontas Co.: Piddling Pit Cave, holotype (USNM 168835), 1 paratype (slide mount in JRH), 1 paratype (USNM), J. R. Holsinger, R. A. Baroody, and R. L. Swensson, 30 Sep 1967.

DIAGNOSIS.—A very small cavernicolous species, closely related to S. parvus and S. pollostus, but distinguished from these species by the bases of pereopods 5–7 which are broader and have well-developed distoposterior lobes and the telson which is proportionately longer (up to 25 percent longer than broad). Further distinguished from S. parvus by having simple lateral sternal gills and from S. pollostus by proportionately narrower gnathopod propods. Largest male, 1.6 mm; largest female, 2.2 mm.

FEMALE.—Antenna 1 about 45 percent length of body, about 40 percent longer than antenna 2; primary flagellum with 7–9 segments. Antenna 2, flagellum with 3 segments. Mouthparts like those of S. pollostus except inner lobes of lower lip vestigial. Propod of gnathopod 1 subequal in size to 2nd propod; palm with double row of 2 spine teeth; defining angle with 2 spine teeth on outside; medial setae absent. Dactyl nail of gnathopod 1 long. Coxal plate of gnathopod 1 longer than broad, with 1 marginal seta. Gnathopod propod 2: palm with 3 spine teeth; defining angle with 1 long spine tooth on outside, smaller one on inside; posterior margin with 1 set setae; medial setae few, singly inserted. Dactyl nail of gnathopod 2 rather long. Coxal plates of gnathopod 2 and pereopod 3 a little longer than broad, with 2 marginal setae each. Coxal plate of pereopod 4 like that of S. pollostus. Pereopod 7 a little longer than pereopod 6, about 50 percent length of body, 25–30 percent longer than pereopod 5. Pereopods 5–7: bases comparatively broad, posterior margins convex, distoposterior lobes distinct and broadly rounded; dactyls relatively long, 45–50 percent length of corresponding propods. Three median sternal gills on pereonites 2–4; 2 pairs simple lateral sternal gills on pereonites 6 and 7; sternal gills absent from pleonite 1. Brood plates sublinear, not expanded distally.

Pleonal plates like those of S. pollostus. Uronites fused. Uropod 1: inner ramus subequal in length to outer ramus, 65–70 percent length of peduncle, armed with 5 spines; outer ramus with 7 spines; peduncle with 5 spines. Uropod 2: inner ramus a little longer than outer ramus, subequal in length to peduncle, armed with 6 spines; outer ramus with 5 spines; peduncle with 2 spines. Uropod 3 lacking ramus, peduncle with 1 apical spine. Telson about 25 percent longer than broad, taptering distally; apical margin entire, with 8 spines.

MALE.—About like female. Peduncular process of uropod 1 small, apex serrate.

TYPE-LOCALITY.—Piddling Pit Cave, located 4.8 km west of Cloverlick on the eastern flank of Cloverlick Mountain in Pocahontas Co., West Virginia, is a fairly extensive cave with several small streams and pools. The cave is developed in the Greenbrier limestone and is in the upper Greenbrier River drainage.

DISTRIBUTION AND ECOLOGY.—This rare species is known only from its type-locality, where it was collected from two mud-bottom pools fed by drips and seeps. As pointed out above, two other species of Stygobromus (S. emarginatus and S. parvus) also inhabit this cave, but on two visits to the cave none of these species has been found together in the same place. The two female paratypes (2.0 and 2.2 mm) had setose brood plates but were not ovigerous.

ETYMOLOGY.—The epithet nanus is from Latin, meaning a “dwarf.”