Stygobromus biggersi Holsinger 1978

Stygobromus biggersi

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

Stygobromus sp.—Franz and Slifer, 1971:26.—Holsinger, Baroody, and Culver, 1976:23.—Holsinger, 1976:76.

MATERIAL EXAMINED.—VIRGINIA. Frederick Co.: Ogdens Cave, holotype (USNM 168795), 25 , 3 paratypes (USNM) and 1 , and 1 paratypes (JRH), J. R. Holsinger, 25 Jan 1969; 2 , 1 paratypes (USNM), A. Wicker, fall, 1968. Additional paratypes as follows: MARYLAND. Washington Co.: Dam No. 4 Cave, 1 (JRH). L. R. Franz, 3 Dec 1965; Hogmaw Cave, 2 (JRH). L. R. Franz, 13 May 1967, and 2 (JRH), 10 Aug 1967. PENNSYLVANIA. Franklin Co.: Needy Cave, 2 (USNM), R. Bray, 22 Feb 1940, and 2 (USNM), 7 Apr 1940. WEST VIRGINIA. Jefferson Co.: Ditmer Cave, 2 (JRH), D. J. Newson, 21 Jun 1967.

DIAGNOSIS.—A medium-sized cavernicolous species distinguished by relatively deep coxal plates of gnathopod 2 and pereopods 3 and 4, broad distoposterior lobe of basis of pereopod 7, distinct and bluntly rounded posterior corners of pleonal plates, and unnotched apical margin of telson. Largest male, 5.6 mm; largest female, 7.0 mm.

FEMALE.—Antenna 1, 50–60 percent length of body, about 50 percent longer than antenna 2; primary flagellum with 13–17 segments. Antenna 2, flagellum with 5 or 6 segments. Mandibles subequal; spine row with 4 or 5 spines; segment 2 of palp with long setae on inner margin, segment 3 with 2 long setae on outer margin, 2 long setae and row of short setae on inner margin, 4 or 5 long setae on apex. Maxilla 1: inner plate with 10 or 11 apical, plumose setae; palp with 6 slender spines and 3 or 4 setae apically and subapically. Maxilla 2, inner plate with oblique row of 11 plumose setae on inner margin. Maxilliped: inner plate with 4 bladelike spines, 3 plumose spines and 2 naked setae apically and subapically, 3 plumose spines (or coarse setae?) on inner margin distally; 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 about 25 percent smaller than 2nd propod; palm slightly convex, armed with double row of 7 or 8 spine teeth; defining angle with 3 long spine teeth of unequal length on outside, 3 or 4 shorter ones on inside; posterior margin with row of about 7 mostly singly inserted setae; medial setae few in number, singly inserted. Dactyl nail of gnathopod 1 relatively short. Segment 5 of gnathopod 1 with 3 rastellate setae. Coxal plate of gnathopod 1 longer than broad, margin with 3 long setae. Gnathopod propod 2: palm slightly convex, armed with double row of 9 or 10 spine teeth; defining angle with 1 long and 2 short spine teeth on outside, 3 short spine teeth on inside; posterior margin with 3 sets setae; medial setae singly inserted. Segment 5 of gnathopod 2 without rastellate setae. Coxal plates of gnathopod 2 and pereopod 3 rather deep, longer than broad, margins with 5 or 6 setae each. Coxal plate of pereopod 4 relatively broad and deep, about as broad as long, reaching about 65 percent length of basis, margin with 7 setae. Pereopod 6 a little longer than pereopod 7, 40–55 percent length of body, 15–25 percent longer than pereopod 5. Pereopods 5–7: basis of 7 broader distally than proximally, bases of 5 and 6 a little broader proximally, distoposterior lobes distinct, broadly rounded; dactyls about 33 percent length of corresponding propods. Coxal gill present on pereopod 7. One median sternal gill on pereonite 2; 2 pairs simple lateral sternal gills on pereonites 6 and 7; sternal gills absent from pleonite 1. Brood plates rather narrow but somewhat expanded distally.

Pleonal plates: posterior margins of 1 and 3 slightly convex, that of 2 nearly straight, margins with 1 seta each; posterior corners distinct, bluntly rounded; ventral margins of plates 2 and 3 with 2 spines each. Uronites free. Uropod 1: inner ramus a little longer than outer ramus, about 75 percent length of peduncle, armed with 12 spines; outer ramus with 8 spines; peduncle with 13 spines. Uropod 2: inner ramus longer than outer ramus, subequal in length to peduncle, armed with 11 spines; outer ramus with 9 spines; peduncle with 4 spines. Uropod 3: ramus about 40 percent length of peduncle, with 3 or 4 apical spines. Telson longer than broad, narrowing distally; apical margin entire, slightly convex, with 11 or 12 spines.

MALE.—Differing slightly from female as follows: Gnathopod propods with 2 or 3 more spine teeth. Coxal gill absent from pereopod 7. Peduncular process of uropod 1 subtriangular, distally serrate.

TYPE-LOCALITY.—Ogdens Cave, located 4 km west-northwest of Middletown in Frederick Co., Virginia, is a medium-sized cave developed in Beek-mantown limestone of lower Ordovician age. The cave contains a small stream and a series of mud-bottom pools fed by drips and seepage and has a moderately rich, troglobitic aquatic fauna consisting of two amphipods (S. gracilipes and S. biggersi), an isopod (Asellus senu lato pricei) and a snail (Fontigens sp.). Stygobromus biggersi is usually fairly abundant in one or more of the pools but has not been found in the stream.

DISTRIBUTION AND ECOLOGY.—The range of this species, which is restricted to a part of the Potomac River drainage basin, extends from Ogdens Cave in northwestern Virginia for approximately 97 km north-northeastward through northeastern West Virginia and central Maryland to Needy Cave in south-central Pennsylvania. The range coincides in part with that of S. gracilipes, and the two species are sometimes found in the same cave. Stygobromus biggersi is predominately an inhabitant of cave pools and is often associated with the isopod Asellus (sensu lato) pricei (Levi). Females (4.9–7.0 mm) with setose brood plates have been collected during all seasons of the year.

ETYMOLOGY.—It is a pleasure to name this species in honor of William W. Biggers, who has accompanied me on many cave trips and has assisted with the collection of subterranean amphipods.