Stygobromus hoffmani Holsinger 1978

Stygobromus hoffmani

Stygonectes species D.—Holsinger, 1969a:32–33.

MATERIAL EXAMINED.—VIRGINIA, Alleghany Co.: Lowmoor Cave, holotype (USNM 168825), 3 and 4 paratypes (JRH), J. R. Holsinger and R. A. Baroody, 18 Jan 1969; McElwee Cave, 53 paratypes (USNM) and 1 paratype on slide mounts (JRH), L. Hubricht, 3 Sep 1949.

DIAGNOSIS.—A relatively small cavernicolous species closely allied morphologically with S. emarginatus, S. morrisoni, and S. mundus, but distinguished from these species by smaller size at sexual maturity, and having fewer flagellar segments of antennae, fewer setae on inner plates of maxillae and on palpal segments 2 and 3 of mandible, fewer spines on palms of gnathopod propods, and fewer spines on uropods 1–3. Further distinguished from S. emarginatus by having fewer setae on peduncular segments 4 and 5 of antenna 2 and fewer sets of setae on posterior margin of propod of gnathopod 2. Largest male, 3.0 mm; largest females, 5.5 mm.

FEMALE.—Antenna 1, 40–42 percent length of body, about 40 percent longer than antenna 2; primary flagellum with 12 or 13 segments. Antenna 2, flagellum with 4 or 5 segments. Mandibles subequal; spine row with 7 spines; segment 2 of palp with 4 long setae, segment 3 with 1 long seta on outer margin, row of short setae on inner margin, 4 long setae on apex. Maxilla 1: inner plate with 5 apical, plumose setae; palp with 2 slender, lightly plumose spines and 3 stiff setae on apex. Maxilla 2, inner plate with oblique row of 4 or 5 plumose setae on inner margin. Maxilliped: inner plate apically with 2 bladelike spines, 2 plumose spines and 3 naked setae; outer plate with row of naked setae on inner margin and apex and 1 apical, plumose seta. Inner lobes of lower lip small.

Propod of gnathopod 1 slightly larger than 2nd propod; palm with double row of 6 spine teeth; defining angle with 3 spine teeth on outside, 3 on inside; inferior medial setae singly inserted, superior medial setae few in number and doubly inserted. Dactyl nail of gnathopod 1 rather long. Coxal plate of gnathopod 1 longer than broad, with 2 marginal setae. Propod of gnathopod 2: palm with double row of 6 or 7 spine teeth; defining angle with 1 long spine tooth on outside, 3 shorter ones on inside; inferior medial setae singly inserted, superior medial setae doubly inserted. Dactyl nail of gnathopod 2 rather long. Coxal plates of gnathopod 2 and pereopod 3 a little longer than broad, margin of 2 with 3 setae, that of 3 with 5 setae. Coxal plate of pereopod 4 about 40 percent length of basis, slightly broader than long, margin with 7 setae. Pereopods 6 and 7 subequal in length, 40–45 percent length of body, about 28 percent longer than pereopod 5. Bases of pereopods 5–7 slightly convex, distoposterior lobes poorly developed. Dactyls of pereopods 6 and 7, 30–35 percent length of corresponding propods; dactyl of pereoped 5 about 45 percent length of corresponding propod. Three median sternal gills on pereonites 2–4; 2 pairs short, bifurcate lateral sternal gills on pereonites 6 and 7; sternal gills absent from pleonite 1. Brood plates sublinear, not expanded distally.

Pleonal plates: posterior margins convex (but nearly straight in plate 2), with 1 seta each; posterior corners small, subacute to narrowly rounded; ventral margins of plates 2 and 3 with 2 spines each. Uronites completely or incompletely fused. Uropod 1: inner ramus subequal in length to outer ramus, 60–65 percent length of peduncle, armed with 9 spines; outer ramus with 10 spines; peduncle with 7 spines. Uropod 2: inner ramus longer than outer ramus and peduncle, armed with 8 spines; outer ramus with 7 spines; peduncle with 3 spines. Uropod 3: ramus about 40 percent length of peduncle, armed apically with 2 spines. Telson longer than broad, gently tapering distally; apical margin with vestigial notch, armed with 13 or 14 spines.

MALE.—Differing from female as follows: antenna with up to 10 primary flagellar segments. Gnathopod propods with 3 or 4 fewer spine teeth. Uropod 1: inner ramus a little longer than outer ramus, armed with 5 spines; outer ramus with 6 spines; peduncle with 5 spines; apical margin of peduncular process serrate. Uropod 2 with few less spines. Telson with 2 or 3 fewer apical spines.

VARIATION.—The lateral sternal gills were longer and more slender on the specimens from the Lowmoor Cave sample.

TYPE-LOCALITY.—Lowmoor Cave, located 6.4 km southwest of Clifton Forge in Alleghany Co., Virginia, is a large maze cave with 4083 meters of surveyed passage (Holsinger, 1975a:43). The cave has a number of drip pools but no flowing stream.

DISTRIBUTION AND ECOLOGY.—Stygobromus hoffmani is known only from two caves which are developed in Upper Silurian limestone and are located about 1.3 km apart on the south side of the Jackson River. Both populations were found in drip pools. The September collection from McElwee Cave contained two ovigerous females (4.0–4.3 mm in length), each of which was carrying three eggs in the brood pouch. Females in the January sample from Lowmoor Cave were sexually immature.