Stygobromus fergusoni Holsinger 1978

Stygobromus fergusoni

Stygobromus species F.—Holsinger, 1969a:30, 44.

MATERIAL EXAMINED.—VIRGINIA. Montgomery Co.: Slussers Chapel Cave, holotype (USNM 168817), 9 , 1 juv. paratypes (USNM), and 1 paratype on slide mounts (JRH), J. R. Holsinger and R. E. Whittemore, 21 Apr 1968; Old Mill Cave, 1 paratype (JRH), L. M. Ferguson, 20 Oct 1969.

DIAGNOSIS.—A medium-sized cavernicolous species closely related to S. emarginatus and S. hoffmani but distinguished from these species by having pereopod 6 a little longer than 7, broader bases of pereopods 5–7, simple lateral sternal gills, and proportionately shorter ramus of uropod 3. Further distinguished from S. emarginatus by the propod of gnathopod 1 which is a little larger than the 2nd and by fewer spine teeth on palms of gnathopod propods. Largest females, 7.0 mm; male unknown.

FEMALE.—Antenna 1, 50–55 percent length of body, 50–60 percent longer than antenna 2; primary flagellum with 19–20 segments. Antenna 2, flagellum with 7 segments. Mandibles subequal; spine row with 7 or 8 spines; segment 2 of palp with 6 setae, segment 3 with 3 long setae on outer margin, row of short setae on inner margin, 4 long setae apically and subapically. Maxilla 1: inner plate with 5 apical, plumose setae; palp with 3 slender spines and 3 stiff setae apically. Maxilla 2, inner plate with oblique row of 8 plumose setae on inner margin. Maxilliped: apex of inner plate as shown; outer plate with row of about 16 naked setae on inner margin and apex and 2 apical, plumose setae. Lower lip with small inner lobes.

Propod of gnathopod 1 a little larger than 2nd propod; palm with double row of 7 or 8 spine teeth; defining angle with 3 long spine teeth on outside, 3 or 4 shorter ones on inside; inferior medial setae singly inserted, superior medial setae few in number, mostly doubly inserted. Dactyl nail of gnathopod 1 rather long. Coxal plate of gnathopod 1 longer than broad, margin with 4 setae. Gnathopod propod 2: palm with double row of 9 spine teeth, plus 2 additional ones on outside; defining angle with 1 long spine tooth on outside, 3 shorter ones on inside; posterior margin with 4 sets setae; inferior medial setae singly inserted, superior medial setae doubly and triply inserted. Dactyl nail of gnathopod 2 proportionately a little shorter than that of 1st gnathopod. Coxal plates of gnathopod 2 and pereopod 3 a little longer than broad, with 5 marginal setae each. Coxal plate of pereopod 4 about as broad as long, about 40 percent length of basis, margin with 8 setae. Pereopod 6 a little longer than 7, 45–50 percent length of body, 20–25 percent longer than pereopod 5. Pereopods 5–7: bases broader proximally than distally, distoposterior lobes poorly developed; dactyls 30–35 percent length of corresponding propods. Three median sternal gills on pereonites 2–4; 2 pairs rather long, simple lateral sternal gills on pereonites 6 and 7; sternal gills absent from pleonite 1. Brood plates sublinear, not much expanded distally.

Pleonal plates: posterior margins slightly convex, with 1 seta each; posterior corners tiny but usually distinct; ventral margin of plate 2 with 2 spines, that of plate 3 with 6 spines. Uronites completely fused. Uropod 1: inner ramus subequal in length to outer ramus, 60–65 percent length of peduncle, armed with 12 spines; outer ramus with 13 spines; peduncle with 12 spines. Uropod 2: inner ramus longer than outer ramus, slightly shorter than peduncle, armed with 12 spines; outer ramus with 8 spines; peduncle with 7 spines. Uropod 3: ramus very short, only about 1/9 length of peduncle, armed with 2 or 3 apical spines. Telson longer than broad, subrectangular; apical margin usually with very small notch, armed with 18 spines.

TYPE-LOCALITY.—Slussers Chapel. Cave, located about 7.3 km north-northeast of Blacksburg in Montgomery Co., Virginia, is a moderately large stream-passage cave developed in Elbrook dolomite of Cambrian age (Holsinger, 1975a: 178–179). The type-series was collected from a series of small, seep fed pools containing bits of decaying wood and troglobitic isopods. Asellus (sensu lato) vandeli Bresson.

DISTRIBUTION AND ECOLOGY.—At present this species is known only from two caves located about 3.7 km apart in a small karst area drained by the North Fork of the Roanoke River. A single ovigerous female, measuring 6.5 mm and carrying 4 embryos in the brood pouch, was collected from a pool in Old Mill Cave in October. The larger females (6.5–7.0 mm) from the April collection in Slussers Chapel Cave had submature brood plates. Males have not been found to date.