Stygobromus grandis Holsinger 1978

Stygobromus grandis

Stygobromus sp.—Holsinger, 1969a:31–32.—Holsinger and Peck, 1971:30.

MATERIAL EXAMINED.—GEORGIA. Chatooga Co.: Parker Cave, holotype (USNM 168824), 1 and 1 paratype (JRH), S. B. Peck and A. Fiske, 20 Jun 1967; 2 paratypes (JRH), J. R. Holsinger, S. B. Peck, R. A. Baroody and A. Fiske, 12 Jun 1967.

DIAGNOSIS.—A large, rather unusual cavernicolous species distinguished from other members of the mackini group by the characters given for the grandis subgroup. Largest male, 12.0 mm; largest females, 19.0 mm.

FEMALE.—Antenna 1, 50 percent length of body, 40 percent longer than antenna 2; primary flagellum with 26–30 segments. Antenna 2, flagellum with 8–10 segments. Mandibles subequal; spine row with 7 spines; segment 2 of palp with row of setae of unequal length on inner margin, segment 3 with 2 long setae on outer margin, row of rather short setae (of unequal length) on inner margin, and 6 long setae apically. Maxilla 1: inner plate with 10 apical, plumose setae; palp with about 12 stiff setae apically and subapically. Maxilla 2, inner plate with oblique row of 9 plumose setae on inner margin. Maxilliped: inner plate with 4 or 5 bladelike spines, 2 plumose spines and 2 or 3 naked setae apically, and 2 plumose spines (or coarse setae?) on inner margin distally; outer plate with naked setae on inner margin and apex. Inner lobes of lower lip vestigial.

Propod of gnathopod 1 a little larger than 2nd propod; palm long, oblique, slightly convex distally, armed with double row of about 23 spine teeth (a few spines on inside near defining angle sometimes trifid and longer than remainder); defining angle with 2 long and 1 short spine teeth on outside, 4 slender spine teeth on inside; posterior margin with cluster of setae on distal 1/3 near defining angle; inferior medial setae singly inserted, superior medial setae reduced to about 2. Dactyl nail of gnathopod 1 very short. Coxal plate of gnathopod 1 proportionately small in comparison with size of propod, longer than broad, margin with 3 setae. Gnathopod propod 2: palm long, oblique, slightly convex distally, armed with double row of 26 or 27 spine teeth, about 5 on inside near defining angle being longer than remainder; defining angle with 1 long and 1 short spine tooth on outside, none on inside; posterior margin with 4 sets setae; inferior medial setae singly inserted, superior medial setae reduced to 1. Dactyl nail of gnathopod 2 very short. Coxal plate of gnathopod 2 proportionately small in comparison with size of propod, longer than broad, margin with 7 setae and 2 spines. Coxal plate of pereopod 3 longer than broad, margin with 10 setae and 2 spines. Coxal plate of pereopod 4 broad and relatively deep, about as broad as long, reaching a little more than 50 percent length of basis, margin with 17 setae. Pereopod 6 a little longer than pereopod 7, 50 percent length of body, 25–30 percent longer than pereopod 5. Bases of pereopods 5–7 with convex posterior margins and broadly rounded distoposterior lobes. Dactyls of pereopods 6 and 7 relatively short, 26–27 percent length of corresponding propods; dactyl of pereopod 5 proportionately longer, about 38 percent length of corresponding propod. Coxal gill present on pereopod 7. Median and pleonite sternal gills absent; 2 pairs rather long, simple lateral sternal gills on pereonites 6 and 7. Brood plates relatively narrow but somewhat expanded distally.

Pleonal plates: posterior margins of plates 1 and 3 slightly convex, that of plate 2 nearly straight, margins with 1 seta each; posterior corners small, distinct, bluntly rounded; ventral margin of plate 2 with 2 spines, that of plate 3 with 4 spines. Uronites free. Uropod 1: inner ramus slightly longer than outer ramus, about 75 percent length of peduncle, armed with 12 spines; outer ramus with 12 spines; peduncle with 13 spines. Uropod 2: inner ramus longer than outer ramus, a little shorter than peduncle, armed with 12 spines; outer ramus with 11 spines; peduncle with 5 spines. Uropod 3: ramus comparatively long, 45–50 percent length of peduncle, armed with 3 or 4 apical spines; peduncle with 3 stiff setae or spinules laterally. Telson longer than broad; apical margin incised 65 percent the distance to base, armed with 14–18 spines.

MALE.—Differing from female as follows: Antenna 1, 60 percent length of body. Antennae with few less flagellar segments. Propod of gnathopod 1 with few less spine teeth on palm. Uropods 1 and 2 with few less spines on rami: peduncular process of uropod 1 absent.

TYPE-LOCALITY.—Parker Cave, located approximately 17.7 km southeast of Lafayette in Chatooga Co., Georgia, is a small cave developed in the Fort Payne limestone of Mississippian age. The cave is located in the Appalachian Valley and in the Coosa River drainage.

DISTRIBUTION AND ECOLOGY.—This species is known only from its type-locality, where it was collected on two occasions from a relatively deep, mud-bottom pool fed by groundwater seepage. On a visit to the cave on 12 June 1967, two females were obtained from this pool which, at that time, was about 1 meter deep. On a return visit eight days later three more specimens (two females and one male) were found in the same pool which, in the interim, had receded to about 0.3 meter in depth. Amphipods presumably gain access to this pool by migration through fissures saturated with groundwater. Of the four females in the type-series, only one 18.0 mm specimen had setose brood plates.

ETYMOLOGY.—The epithet grandis is from Latin, meaning “large,” “great,” or “magnificent.”

The cumberlandus Group

DIAGNOSIS.—Adults relatively small. Mature female larger than mature male. Inner lobes of lower lip small to vestigial. Propod of gnathopod 1 smaller than 2nd propod; palm only about ½ length of propod; defining angle with several long spine teeth on outside, some of which may be serrate on distal half; posterior margin subequal in length to palm, with row of mostly singly inserted setae. Segment 5 of gnathopod 1 usually with rastellate setae. Propod of gnathopod 2: palm rather long and oblique; posterior margin rather short, with 2–4 sets setae. Segment 5 of gnathopod 2 without rastellate setae. Pereopod 6 a little longer than pereopod 7. Pereopod 7 without coxal gill. Lateral sternal gills simple. Pleonal plates: posterior margins with 1 to several setae each; posterior corners small to indistinct. Uronites free. Ramus of uropod 3 with 2 or 3 apical spines. Telson subquadrate, apical margin with small notch.