Stygobromus wengerorum Holsinger 1974

Stygobromus wengerorum

MATERIAL EXAMINED.—CALIFORNIA. Mariposa Co.: Bower Cave, holotype female (USNM 142821) and 5 paratypes (JRH), Steve Shimek, 16 May 1971; 3 paratypes (USNM 142822), Bill Kruse, 16–18 July 1971.

DIAGNOSIS.—A relatively large cavernicolous species, closely related to, but distinguished from, other cavernicolous species of the Mother Lode region by proportionately larger gnathopodal propods with more spine teeth on palms, and more spines on the ventral margins of the pleonal plates. Largest females, 10.0 mm; male unknown.

DESCRIPTION.—Antenna 1: 55 percent as long as body, 50 percent longer than antenna 2; primary flagellum with 18 to 20 segments. Antenna 2: peduncular segments 3 and 4 with numerous slender spines and long setae (as in S. grahami); flagellum with 7 segments. Mandibles subequal, about like S. grahami except for few less spines in spine row. Maxilla 1: inner plate with 11 plumose setae apically; palp with 6 spines and 2 setae apically and subapically. Maxilla 2: inner plate with oblique row of 14 or 15 plumose setae on inner margin. Maxilliped: inner plate with 5 bladelike spines (some with small bristles), 3 or 4 plumose spines and 3 setae apically and row of plumose spines or stiff setae on inner margin; outer plate like that of S. grahami. Lower lip with small inner lobes.

Gnathopodal Propod 1: Palm long, oblique, slightly convex, armed with double row of 13 spine teeth; area of posterior angle long, with 7 spine teeth (some forked) and 2 setae on outside, 8 mostly forked spine teeth on inside; posterior margin short, about one-fourth the length of palm; medial setae singly inserted. Coxal plate of gnathopod 1 longer than broad, with 2 marginal setae. Gnathopodal propod 2 proportionately large, more than twice the size of 1st propod, 10 percent as long as body in larger females; palm very long, oblique, convex distally, concave proximally, armed with double row of 13 spine teeth, plus 4 additional spine teeth on outside; posterior angle with 1 long spine tooth and 5 setae on outside, 3 spine teeth on inside; posterior margin proportionately short, about one-third the length of palm, with 1 set of 5 setae just below defining angle and 1 short seta about half the distance to base; medial setae mostly singly inserted; dactyl long, curved, nail rather short. Coxal plates of gnathopod 2 and pereopod 3 longer than broad, plate 2 with 6 marginal setae, plate 3 with 9 marginal setae; coxal plate of pereopod 4 about as long as broad, with 9 marginal setae. Pereopod 6 a little longer than pereopod 7, 55 to 60 percent as long as body, 20 percent longer than pereopod 5. Bases of pereopods 5–7 rather long, a little broader proximally than distally; distoposterior lobes rather small, distinct, bluntly rounded. Dactyls of pereopods 6 and 7, 25 to 30 percent as long as corresponding propods. Coxal gills present on pereopods 2–6. Sternal blisters present on pereonites 2–7. Brood plates of mature females small and narrow.

Pleonal Plates: Posterior margins of plates 1 and 2 nearly straight, that of plate 3 convex; posterior corners distinct, rounded; ventral margin of plate 1 with 2 spines, plate 2 with 5 spines, plate 3 with 7 spines. Uropod 1: inner ramus subequal in length to outer ramus, about three-fourths the length of peduncle, armed with 12 or 13 spines; outer ramus with 12 or 13 spines; peduncle with 10 to 12 spines. Uropod 2: inner ramus a little longer than outer ramus, equal in length to peduncle, armed with 11 or 12 spines; outer ramus with 11 spines; peduncle with 5 spines. Uropod 3: ramus slightly less than half the length of rather broad peduncle, with 4 apical spines. Telson about one-third longer than broad; apical margin with shallow notch; apical lobes with 6 or 7 spines each.

TYPE-LOCALITY.—Bower Cave, about 8 miles east of Coulterville, Mariposa County, California. The type-locality is a deep, partly water-filled cave developed in vertically bedded marble or limestone of the Calaveras formation (Halliday, 1962). For the past several years this cave has been extensively explored by members of the Bower Cave Diving Group of Palo Alto, California. The May sample of six females was collected from a depth of 125 feet beneath the surface of the cave lake, where numerous specimens had been attracted by liver bait. The July sample of three females was collected at depths of 65 to 125 feet on the silt-covered floor of the main passage of the cave. The cave lake is also inhabited by an undescribed, troglobitic species of the planarian genus Sphalloplana (Roman Kenk, pers. comm.).

DISTRIBUTION AND ECOLOGY.—This species is known only from the type-locality, although according to Steve Shimek (in litt.), a small population of amphipods (probably Stygobromus) has been seen in nearby Centipede Cave. Three females with setose brood plates were observed in the May collection (size = 9.0 to 10.0 mm) and two were observed in the July collection (size = 8.0 and 8.5 mm).

ETYMOLOGY.—At the request of the Bower Cave Diving Group, I have named this species in honor of the venerable Clara and George Wenger who have made significant contributions to the study of Bower Cave.

Stygobromus wengerorum, commonly called Wenger's cave amphipod, is a troglomorphic species of amphipod in family Crangonyctidae. It is endemic to two caves in Mariposa County, California in the United States.