Stygobromus pollostus Holsinger 1978

Stygobromus pollostus

Apocrangonyx sp.—Culver, 1973:103.—Holsinger, Baroody, and Culver, 1976:22.

MATERIAL EXAMINED.—WEST VIRGINIA. Greenbrier Co.: Arbuckles Cave, holotype (USNM 168842), 1 paratype (slide mounts in JRH) and 1 paratype (USNM), D. C. Culver and R. A. Baroody, Oct 1970; Parlor Cave, 3 paratypes (JRH), J. R. Holsinger, R. A. Baroody, and H. DuChene, 27 Apr 1969; Monroe Co.: Haynes Cave, 4 paratypes (1 in JRH, 3 in USNM), 1 paratype (USNM), J. R. Holsinger, D. C. Culver, and R. A. Baroody, 6 Apr 1971; Pocahontas Co.: Snedegars Cave, 1 , 2 juv. paratypes (JRH), D. C. Culver, and R. A. Baroody, 3 Jul 1972.

DIAGNOSIS.—A small cavernicolous species distinguished from S. parvus, to which it is very closely related, by the gnathopod propods, which are proportionately broader proximally, the telson, which tapers distally and has fewer spines, and by smaller size at sexual maturity. Largest male, 2.3 mm; largest females, 2.5 mm.

FEMALE.—Antenna 1, 40–50 percent length of body, 40–50 percent longer than antenna 2; flagellum with 7–9 segments. Antenna, 2, flagellum with 3 segments. Mandibles subequal; spine row with 3 spines; segments 2 of palp with 1 long seta on inner margin distally, segment 3 with 1 long seta on outer margin, 4 long setae apically. Maxilla 1: inner plate with 2 apical, plumose setae; palp with 4 setae apically. Maxilla 2, inner plate with oblique row of 2 plumose setae on inner margin. Maxilliped: inner plate with 2 bladelike spines, 1 plumose spine and 1 naked seta apically, 1 plumose spine (or seta) and 1 naked seta subapically; outer plate with few setae on inner margin and apex and 1 plumose seta apically. Inner lobes of lower lip small but distinct.

Propod of gnathopod 1 a little larger than 2nd propod; palm armed with 2 spine teeth; defining angle with 2 or 3 long spine teeth on outside, 1 or 2 shorter ones on inside; medial setae few, singly inserted. Dactyl nail of gnathopod 1 elongate, nearly 50 percent as long, or sometimes more than 50 percent longer than, dactyl. Coxal plate of gnathopod 1 longer than broad, with 1 marginal seta. Gnathopod propod 2: palm with 2 spine teeth; defining angle with 1 or 2 long spine teeth on outside, 1 or 2 shorter ones on inside: posterior margin with 1 or 2 setae; medial setae few, singly inserted. Dactyl nail of gnathopod 2 elongate like that of 1st gnathopod. Coxal plates of gnathopod 2 and pereopod 3 about as broad as long, with 1 or 2 marginal setae each. Coxal plate of pereopod 4 shallow, broader than long, reaching about 20 percent length of basis, margin with 2 setae. Pereopod 7 a little longer than pereopod 6, 35–40 percent length of body (occasionally up to 50 percent), 30–35 percent longer than pereopod 5. Pereopods 5–7: bases relatively narrow, with few marginal setae and spines, posterior margins nearly straight, distoposterior lobes poorly developed; dactyls long, 40–50 percent length of corresponding propods. Three median sternal gills on pereonites 2–4; 2 pairs lateral sternal gills on pereonites 6 and 7, sometimes simple, sometimes bifurcate but with branches of unequal length; sternal gills absent from pleonite 1. Brood plates sublinear, not expanded distally.

Pleonal plates: posterior margins weakly convex, with 1 relatively long seta each; posterior corners indistinct, broadly rounded; ventral margin of plate 3 with 1 spine. Uronites fused. Uropod 1: inner ramus a little longer than outer ramus, about 65 percent length of peduncle, armed with 6 spines; outer ramus with 5 or 6 spines; peduncle with 4–6 spines. Uropod 2: inner ramus longer than outer ramus, about 80 percent length of peduncle, armed with 6 spines; outer ramus with 4 or 5 spines; peduncle with 2 or 3 spines. Uropod 3: ramus lacking; peduncle with 1 apical spine. Telson a little broader than long, gently tapering distally; apical margin entire, armed with 6 spines.

MALE.—Differing only slightly from female as follows: Peduncular process of uropod 1 very short, apical margin serrate. Telson about as broad as long, apical margin with 6–8 spines.

VARIATION.—Specimens from Arbuckles Cave (middle of the range) and Haynes Cave (southern end of the range) had bifurcate lateral sternal gills, whereas those from Snedegars Cave (northern end of the range) and Parlor Cave (near middle of the range) had simple lateral sternal gills. There was also some slight but insignificant variation in the arrangement of spine teeth on the gnathopod in different populations.

TYPE-LOCALITY.—Arbuckles Cave, located 7.9 km north-northeast of the center of Lewisburg in Greenbrier Co., West Virginia, is a small, mostly dry cave with intermittent drip pools. It is developed in the Greenbrier limestone.

DISTRIBUTION AND ECOLOGY.—This species is recorded from four caves in the Greenbrier Valley of West Virginia. The range covers a linear distance of 40 km and is separated from that of S. parvus by a distance of about 48 km. Stygobromus pollostus is found in tiny, usually intermittent, drip pools, where it occurs only sporadically. Females (2.0–2.3 mm) with setose brood plates have been observed in April collections from Parlor and Haynes caves.