Stygobromus redactus Holsinger 1978

Stygobromus redactus

Stygobromus species G.—Holsinger, 1969a:30.

Stygobromus n. sp. 1.—Culver, Holsinger, and Baroody, 1973: 691.

Stygobromus sp.—Holsinger, Baroody, and Culver. 1976:23.

MATERIAL EXAMINED.—WEST VIRGINIA. Monroe Co.: Patton Cave, holotype (USNM 168851), 1 , 1 , 1 juv. paratypes (USNM) and 1 paratype (slide mounts in JRH), J. R. Holsinger, 11 May 1966.

DIAGNOSIS.—A very small cavernicolous species distinguished from other members of the ephemerus group by the proportionately small gnathopod propods which have reduced numbers of spines and setae, possession of small ramus on uropod 3, and proportionately short telson which is broader than long. Largest males, 2.0 mm; largest female, 2.0 mm.

MALE.—Antenna 1, 45–50 percent length of body, 40–50 percent longer than antenna 2; primary flagellum with 10 segments. Antenna 2, flagellum with 4 or 5 segments. Mandibles subequal; spine row with 3 spines; segment 2 of palp with 1 long seta on inner margin distally, segment 3 with coarse setae on inner margin and 4 setae (2 long, 2 short) apically. Maxilla 1: inner plate with 2 apical, plumose setae; palp with 4 thick setae apically. Maxilla 2, inner plate with oblique row of 2 plumose setae on inner margin. Maxilliped: inner plate with 1 bladelike spine, 2 plumose spines, and 1 naked seta apically, 1 naked seta and 1 plumose spine (or seta) subapically; outer plate with few naked setae apically and subapically, 1 plumose seta on apex. Inner lobes of lower lip lacking.

Propod of gnathopod 1 a little larger than 2nd propod; palm with 2 spine teeth; defining angle with 2 spine teeth on outside, 1 on inside; medial setae absent. Dactyl nail of gnathopod 1 nearly 50 percent length of dactyl. Coxal plate of gnathopod 1 longer than broad, margin with 1 seta. Gnathopod propod 2; palm with 1 spine tooth; defining angle with 1 spine tooth on outside, 1 on inside; posterior margin with 1 thick seta; medial setae reduced to 1. Dactyl nail of gnathopod 2 long. Coxal plates of gnathopod 2 and pereopod 3 shallow, broader than long, margins with 1 seta each. Coxal plate of pereopod 4 shallow, broader than long, reaching about 25 percent length of basis, margin with 2 setae. Pereopods 6 and 7 subequal in length, about 50 percent length of body, 25–30 percent longer than pereopod 5. Pereopods 5–7; posterior margins of bases weakly convex, distoposterior lobes poorly developed; dactyls relatively long, about 45 percent length of corresponding propods. Three long sternal gills on pereonites 2–4; 2 pairs simple lateral sternal gills on pereonites 6 and 7; sternal gills absent from pleonite 1.

Pleonal plates: posterior margins weakly convex, with 1 seta each; posterior corners indistinct, broadly rounded; ventral margin of plate 3 with 1 spine. Uronites partly fused, suture visible between 1 and 2. Uropod 1: inner ramus longer than outer ramus, 60–65 percent length of peduncle, armed with 7 spines; outer ramus with 5 spines; peduncle with 5 spines; peduncular process short, apex broad and serrate. Uropod 2: inner ramus longer than outer ramus, subequal in length to peduncle, armed with 6 spines; outer ramus with 4 spines; peduncle with 2 spines. Uropod 3: ramus short, about 1/6 length of peduncle, with 1 apical spine. Telson short, broader than long, gently tapering distally; apical margin entire or with very tiny notch, armed with 6 spines.

FEMALE.—About like male. Brood plates sublinear, not expanded distally.

TYPE-LOCALITY.—Patton Cave, located 2.4 km southeast of Gap Mills in Monroe Co., West Virginia, is a moderately large cave developed in Middle Ordovician limestone. The cave opens in a narrow karst valley formed just west of Peters Mountains and is situated in the Greenbrier River drainage.

DISTRIBUTION AND ECOLOGY.—This rare species is known only from its type-locality, where it was collected from a small, mud-bottom pool fed by seepage. Amphipods were observed burrowing in the soft mud substrate of the pool. The largest female (2.0 mm) in the type series had setose brood plates.