Stygobromus interitus Holsinger 1978

Stygobromus interitus

Stygobromus sp. H.—Holsinger, 1969a:31.

MATERIAL EXAMINED.—VIRGINIA. Craig Co.: New Castle Murder Hole (cave), holotpye partly on slide mounts (USNM 168828) and 1 paratype (USNM), H. W. Jackson, 31 Oct 1943.

DIAGNOSIS.—A relatively small cavernicolous species distinguished from S. cumberlandus, with which it is apparently closely allied morphologically, by proximally broader propod of gnathopod 1, lacking serrate spine teeth at defining angle of 1st gnathopod propod, shorter coxal plate of pereopod 4 which reaches only about 40 percent length of basis, more than 1 seta each on posterior margins of pleonal plates, 2 apical spines on ramus of uropod 3, and 8 apical spines on telson. Largest female, 4.2 mm; male unknown.

FEMALE.—Antenna 1, 40 percent length of body, 40–45 percent longer than antenna 2; primary flagellum with 10 segments. Antenna 2, flagellum with 4 or 5 segments. Mandibles subequal; spine row with 3 or 4 spines; segment 2 of palp with about 5 setae on inner margin, segment 3 with 1 long seta on outer margin, row of 2 long and several shorter setae on inner margin, and 4 long setae on apex. Maxilla 1: inner plate with 5 apical, plumose setae; palp with 2 slender spines and 4 setae apically. Maxilla 2, inner plate with oblique row of 6 plumose setae on inner margin. Maxilliped: inner plate with 2 bladelike spines, 1 plumose spine and 1 or 2 naked setae apically, 3 plumose spines (or coarse setae?) subapically; outer plate with naked setae on inner margin and apex, and 1 plumose seta apically. Inner lobes of lower lip small.

Propod of gnathopod 1 between 1/2 and 2/3 the size of 2nd propod; palm slightly convex, armed with partly unequal double row of about 6 or 7 spine teeth; defining angle with 2 spine teeth of unequal length on outside, 2 shorter trifid spine teeth on inside; posterior margin with row of about 8 mostly singly inserted setae; medial setae singly inserted. Dactyl nail of gnathopod 1 moderately long. Segment 5 of gnathopod 1 with 2 small rastellate setae. Coxal plate of gnathopod 1 longer than broad, margin with 3 setae. Gnathopod propod 2: palm long, nearly straight, armed with double row of 7 spine teeth; defining angle with 2 long spine teeth on outside, 2 shorter ones on inside; posterior margin with 3 sets setae; inferior medial setae singly inserted, superior medial setae absent. Coxal plates of gnathopod 2 and pereopod 3 longer than broad, margins with 4 setae each. Coxal plate of pereopod 4 about as broad as long, reaching about 40 percent length of basis, margin with 6 setae. Pereopod 6 a little longer than pereopod 7, 40–45 percent length of body, 30–35 percent longer than pereopod 5. Bases of pereopods 5–7 nearly straight to slightly convex; distoposterior lobes distinct, bluntly rounded. Dactyls of pereopods 6 and 7 about 35 percent length of corresponding propods; that of pereopod 5 about 30 percent length of propod. Coxal gill absent from pereopod 7. Three long median sternal gills on pereonites 2–4; 2 pairs simple, lateral sternal gills on pereonites 6 and 7; 1 pair sternal gills on pleonite 1. Brood plates not fully mature in specimens examined but apparently not much expanded distally.

Pleonal plates: posterior margins convex, with 3 or 4 setae each; posterior corners of plates 1 and 2 indistinct, that of plate 3 small but distinct; ventral margin of plate 2 with 2 spines, that of plate 3 with 3 spines. Uronites free. Uropod 1: inner ramus equal in length to outer ramus, about 55 percent length of peduncle, armed with 12 spines; outer ramus with 8 spines; peduncle with 17 spines. Uropod 2: inner ramus longer and thicker than outer ramus, shorter than peduncle, armed with 9 spines; outer ramus with 6 spines; peduncle with 4 spines. Uropod 3: ramus about 1/4 length of peduncle, with 2 apical spines. Telson about as broad as long; apical margin with slight notch, armed with 8 spines.

TYPE-LOCALITY.—New Castle Murder Hole, located 4.8 km southwest of New Castle in Craig Co., Virginia, is a large, deep cave developed in Middle Ordovician limestone. The cave lies just east of a limestone drainage divide between the New and James river watersheds (see “Distribution and Ecology” under S. estesi).

DISTRIBUTION AND ECOLOGY.—This rare species is known only on the basis of two females collected in October 1943. Although the habitat was not specified on the collection label, presumably, given the make-up of the cave, the specimens were taken from a pool. Neither female had setose brood plates but the holotype appeared to be at least submature.