Stygobromus stegerorum Holsinger 1978

Stygobromus stegerorum

Stygobromus sp. D.—Holsinger, 1969a:29–30.

MATERIAL EXAMINED.—VIRGINIA. Augusta Co.: Madisons Saltpetre Cave, holotype (USNM 168855), 2 paratypes (USNM), 1 and 1 paratypes (JRH), J. R. Holsinger and R. W. Burnette, 24 Aug 1964; 1 paratype (JRH), R. M. Norton, Sep 1970; 1 paratype (USNM), J. A. Estes and G. W. Dickson, 19 Mar 1975; Stegers Fissure, 1 paratype (JRH), J. R. Holsinger, S. W. Hetrick, and J. A. Estes, 8 Jun 1974.

DIAGNOSIS.—A medium-sized cavernicolous species distinguished by long, slender antennae, pereopods, and uropods 1 and 2, long, narrow coxal plate of pereopod 3, large, deep coxal plate of pereopod 4, and relatively long telson which is nearly 50 percent broader proximally than distally and has distinct apical notch. Largest males, 5.5 mm; largest female, 6.8 mm.

MALE.—Antenna 1, 70–90 percent length of body, 35–40 percent longer than antenna 2; primary flagellum with 20–21 segments. Antenna 2, flagellum with 5 segments. Mandibles subequal; spine row with 5 spines; segment 2 of palp with 4 long and 2 short setae on inner margin, segment 3 with 1 long seta on outer margin, 1 long seta and row of short setae on inner margin, 4 long setae on apex. Maxilla 1: inner plate with 9 apical, plumose setae; palp with 2 slender spines and 4 stiff setae apically. Maxilla 2, inner plate with oblique row of 9 plumose setae on inner margin. Maxilliped: inner plate with 2 bladelike spines, 2 plumose setae and 1 naked seta apically, 1 bladelike spine, 2 naked setae and row of 4 plumose setae subapically; outer plate with naked setae on inner margin and apex, and 1 plumose seta apically. Inner lobes of lower lip absent.

Propod of gnathopod 1 shorter than 2nd propod; palm oblique, margin straight, armed with unequal double row of 16 or 17 spine teeth; defining angle without long spine teeth on outside; posterior margin with 2 setae; medial setae few in number, singly inserted. Dactyl nail of gnathopod 1 relatively long. Segment 5 of gnathopod 1 with 1 rastellate seta. Coxal plate of gnathopod 1 longer than broad, margin with 5 or 6 setae. Gnathopod propod 2: palm long, oblique, slightly convex, armed with double row of about 13 spine teeth; defining angle with 1 long spine tooth on outside, 2 shorter ones on inside; medial setae singly inserted. Dactyl nail of gnathopod 2 relatively long. Segment 5 of gnathopod 2 without rastellate setae. Coxal plate of gnathopod 2 rather deep, longer than broad, margin with 4 or 5 setae. Coxal plate of pereopod 3 long and rather narrow, reaching about 60 percent length of basis, margin with 6 setae. Coxal plate of pereopod 4 broad and deep, reaching about 70 percent length of basis, margin with 9–11 setae. Pereopod 6 a little longer than pereopod 7, about 60 percent length of body, about 10 percent longer than pereopod 5. Pereopods 5–7: bases broader proximally than distally, distoposterior lobes relatively small; dactyls of 6 and 7 about 33 percent length of corresponding propods, that of 5 about 37 percent length of corresponding propod. Coxal gill absent from pereopod 7. 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.

Pleonal plates: posterior margins of 1 and 2 nearly straight, that of 3 slightly convex, margins with 1 seta each; posterior corners distinct, bluntly rounded; ventral margin of plate 3 with 1 spine. Uronites free. Uropod 1: inner ramus a little longer than outer ramus, about 85 percent length of peduncle, armed with 15 spines; outer ramus with 14 spines; peduncle with 11 spines; peduncular process comparatively short, outer margin rugose. Uropod 2: inner ramus broader and longer than outer ramus, longer than peduncle, armed with 15 spines; outer ramus with 13 spines; peduncle with 2 spines. Uropod 3: ramus about 1/3 length of peduncle, with 2 or 3 apical spines; peduncle with 1 distal spine. Telson longer than broad, tapering distally; apical margin incised about 20 percent the distance to base, armed with 8–10 spines.

FEMALE.—Differing only slightly from male as follows: Propod of gnathopod 1 with few less spine teeth; segment 5 of gnathopod 1 with 3 rastellate setae. Propod of gnathopod 2 with few more spine teeth. Brood plates relatively narrow but somewhat expanded distally.

TYPE-LOCALITY.—Madison Saltpetre Cave, located in Augusta Co., Virginia, is developed in Cave Hill which lies just west of Grottoes and just west of South River (upper Potomac River drainage). The cave is comparatively small and is developed in limestone or dolomite of the Cambrian-aged Conococheague Formation. Two deep lakes of phreatic water occur on the lower level, both of which are occupied by S. stegerorum and the troglobitic cirolanid isopod Antrolana lira Bowman.

DISTRIBUTION AND ECOLOGY.—Outside of the type-locality, this species has been collected from a deep pool of phreatic water at the bottom of Stegers Fissure which is a 4.5-meter-deep vertical crevice situated about 152 meters north of Madison Saltpetre Cave. The water in this fissure, which is probably continuous through subterranean crevices with that in the deep lakes in Madison Saltpetre Cave, is also inhabited by cirolanid isopods. Two females, measuring 6.0 and 6.8 mm in length and collected in March and June, respectively, had setose brood plates.

ETYMOLOGY.—It is a pleasure to name this species in honor of Mr. and Mrs. Lyall O. Steger, the owners of Madisons Saltpetre Cave, who have generously offered their cooperation in allowing us to study the interesting fauna of their cave.