Stygobromus baroodyi Holsinger 1978

Stygobromus baroodyi

Stygobromus sp. E.—Holsinger, 1969a:29–31.

MATERIAL EXAMINED.—VIRGINIA. Rockbridge Co.: Bathers Cave, holotype (USNM 168791), 20 and 4 juv. paratypes (USNM), 1 paratype on slide mounts (JRH), J. R. Holsinger, R. A. Baroody, R. M. Norton, and R. W. Burnette, 17 Apr 1965; Billy Williams Cave, 1 paratype (JRH), J. R. Holsinger and J. E. Cooper, 27 May 1961, and 6 paratypes (JRH), J. R. Holsinger, R. W. Burnette and R. M. Norton, 17 Apr 1965; Buck Hill Cave, 2 paratypes (JRH), T. C. Barr, Jr., 2 Jan 1959; cave between Lexington and Buena Vista (probably Bell Cave), 5 paratypes (USNM), J. A. Fowler, 31 Oct 1943; Grahams Cave, 1 paratype (JRH), J. Tichenor, Dec 1970; Showalters Cave, 1 , 1 juv. paratypes (JRH), R. M. Norton, 17 Apr 1965, and 2 , 3 paratypes (JRH), J. R. Holsinger, J. H. Carpenter and T. G. Marsh, 13 July 1969.

DIAGNOSIS.—A medium-sized cavernicolous species distinguished by rather long, nonsetose posterior margin and slightly concave palm of gnathopod propod 1, small rastellate setae on segment 5 of gnathopods, small, often acute posterior corners of pleonal plates, and relatively short, unnotched telson. Largest males, 7.0 mm; largest female, 11.9 mm.

FEMALE.—Antenna 1, 50–60 percent length of body, 50 percent longer than antenna 2; primary flagellum with up to 32 segment. Antenna 2, flagellum with up to 9 segments. Mandibles subequal; spine row with 9 spines; segment 2 of palp with row of rather long setae on inner margin, segment 3 with 1 long seta on outer margin, row of short setae on inner margin and 4 long setae on apex. Maxilla 1: inner plate with 9 apical, plumose setae; palp with 2 spines and 5 setae apically and subapically. Maxilla 2, inner plate with oblique row of 8 or 9 plumose setae on inner margin. Maxilliped: inner plate with 3 bladelike (often serrate) spines, 2 plumose spines and 2 naked setae apically, 3 plumose spines (or coarse setae?) on inner margin distally; outer plate with naked setae on inner margin and apex, and 2 or 3 spines (or thick setae) and 1 plumose seta apically. Inner lobes of lower lip small to vestigial.

Propod of gnathopod 1 slightly smaller than 2nd propod; palm slightly concave, armed with double row of 9 spine teeth; defining angle with 5 spine teeth on outside, 5 spine teeth on inside; posterior margin about 50 percent length of palm, without setae; medial setae singly and doubly inserted. Dactyl nail of gnathopod 1 relatively short. Segment 5 of gnathopod 1 with several small, poorly developed rastellate setae. Coxal plate of gnathopod 1 longer than broad, margin with 4 setae. Gnathopod propod 2: palm oblique, margin nearly straight, armed with double row of 11 or 12 spine teeth; defining angle with 1 long spine tooth on outside, 1 short spine tooth on inside; posterior margin with 4 sets setae; inferior medial setae singly inserted, superior medial setae singly, doubly, and triply inserted. Dactyl nail of gnathopod 2 relatively short. Segment 5 of gnathopod 2 with several very small, poorly developed rastellate setae. Coxal plate of gnathopod 2 longer than broad, margin with 1 or 2 small spines and 4 or 5 setae. Coxal plate of pereopod 3 longer than broad, margin with 3 short spines and 6 setae. Coxal plate of pereopod 4 about as broad as long, reaching about 45 percent length of basis, margin with 10 setae. Pereopod 7 usually a little longer than, but occasionally about equal to, pereopod 6, 45–55 percent length of body, 20–30 percent longer than pereopod 5. Bases of pereopods 5–7 a little broader proximally than distally, distoposterior lobes distinct, bluntly rounded. Dactyls of pereopods 6 and 7 about 25 percent length of corresponding propods; dactyl of pereopod 5 about 33 percent length of corresponding propods. Coxal gill present on pereopd 7. Three median sternal gills on pereonites 2–4; 2 pairs bifurcate lateral sternal gills on pereonites 6 and 7; 1 pair sternal gills on pleonite 1. Brood plates relatively narrow but somewhat expanded distally.

Pleonal plates: posterior margins slightly convex, each with 1 setae inserted well above posterior corner; posterior corners small, subacute to acute; ventral margin of plate 1 with 5 spines, that of plate 2 with 3 spines. Uronites free. Uropod 1: inner ramus equal in length to outer ramus, about 60 percent length of peduncle, armed with 12 spines; outer ramus with 13 spines; peduncle with 11 spines. Uropod 2: inner ramus longer than outer ramus, subequal in length to peduncle, armed with 11 spines; outer ramus with 8 spines; peduncle with 4 spines. Uropod 3: ramus about 30 percent length of peduncle, with 3 rather short apical spines. Telson about as broad as long; apical margin entire but with small break in spine row, armed with 14–16 moderately short spines.

MALE.—Differing from female as follows: Propod of gnathopod 2 with 3 or 4 more spine teeth. Peduncular process of uropod 1 rounded apically, margin of distal half serrate. Uropod 3: ramus, 20–25 percent length of peduncle, with 3 rather long apical spines; peduncle with 1 small spine distolaterally. Telson slightly longer than broad; apical margin entire, armed with 16 spines, most of which are relatively long.

TYPE-LOCALITY.—Bathers Cave, located 3.2 km north of Lexington in Rockbridge Co., Virginia, is a medium-sized cave developed in Middle Ordovician limestone. In this cave, amphipods are fairly abundant in a series of small, mud-bottom stream pools about 91 m from the entrance.

DISTRIBUTION AND ECOLOGY.—The range of this species, which as presently known is limited to Rockbridge County, lies within the James River drainage basin and covers a linear distance of about 42 km. Stygobromus baroodyi is commonly associated with small, slow-flowing cave streams with mud or silt bottoms. It has also been taken from mud-bottom drip and seep pools. Females with setose brood plates, ranging in size from 7.5–11.9 mm, have been collected during all seasons of the years.