Stygobromus grahami Holsinger 1974

Stygobromus grahami

MATERIAL EXAMINED.—CALIFORNIA. Calaveras Co.: Cave of the Catacombs, holotype female (USNM 142781) and 17 paratypes (USNM 142782), R. E. Graham, 22 Aug. 1963; Sink Cave, 5 paratypes (JRH), P. Hara, 7 June 1971; Cave City Cave, 1 paratype (USNM 142783), collector unknown, 7 Feb. 1954; Cave of the Quills, 10 paratypes (JRH), R. E. Graham, 14 May 1960; Shaws Cave, 2 collections of paratypes (JRH), R. E. Graham, 15 Aug. 1962 and 21 Aug. 1963; Amador Co.: Soldier Creek Cave, 2 paratypes (JRH), R. E. Graham, 3 Sept. 1961.

DIAGNOSIS.—A medium-sized cavernicolous species distinguished from other species of the hubbsi group described above by 15 or 16 plumose setae on the apex of the inner plate of maxilla 1 and on the inner margin of the inner plate of maxilla 2; 12 or 13 apical spines on the inner plate of the maxilliped; row of forked spine teeth on the inside margin of the posterior angle of gnathopodal propod 1; proportionately large gnathopodal propod 2 of the female with distally concave palm (excepting S. hubbsi); deep coxal plates of gnathopod 2 and pereopods 3 and 4; more spines on the ventral margins of pleonal plates 2 and 3 (excepting S. hubbsi); and the presence or absence of sternal blisters (excepting S. elliotti). Largest females, 9.0 mm; largest males, 5.0 mm.

FEMALE.—Antenna 1: 60 to 65 percent as long as body, 40 to 55 percent longer than antenna 2; primary flagellum with 20 to 24 segments. Antenna 2: peduncular segments 4 and 5 with numerous slender spines and stiff setae marginally; flagellum with 8 or 9 segments. Mandibles subequal; spine row with 10 or 11 spines; palpal segment 2 with 9 long setae on inner margin; palpal segment 3 with row of very short setae on inner margin, 5 long setae on apex. Maxilla 1: inner plate with 15 or 16 plumose setae apically; palp with 7 small spines and 4 or 5 setae apically and subapically. Maxilla 2: inner plate with 7 bladelike (some serrate) spines, 5 or 6 plumose spines and 3 or 4 setae apically and row of plumose spines (or stiff setae) on inner margin; outer plate with 1 or 2 bladelike spines and 7 or 8 setae apically. Lower lip with small inner lobes.

Gnathopodal Propod 1: Palm oblique, convex, armed with double row of 7 or 8 spine teeth; posterior angle with 4 spine teeth on outside, 6 forked spine teeth on inside; posterior margin with 1 short seta submarginally just below defining angle; medial setae mostly singly inserted; dactyl nail rather long. Coxal plate of gnathopod 1 longer than broad, with 3 marginal setae. Gnathopodal propod 2 up to 3 times size of 1st propod; palm long, oblique, convex proximally, concave distally, armed with double row of 9 spine teeth plus 4 additional spine teeth on outside; posterior angle with 1 long spine tooth and several setae on outside, 2 shorter spine teeth on inside; posterior margin short, less than one-half the length of palm, with short row of long setae just below defining angle; inferior medial setae singly inserted, superior medial setae singly and triply inserted; dactyl long and curved, nail short. Coxal plates of gnathopod 2 and pereopod 3 longer than broad, with 8 or 9 marginal setae each. Coxal plate of pereopod 4 rather deep, about half the length of segment 2, about as broad as long, expanded distally, with 13 marginal setae. Pereopod 6 a little longer than pereopod 7, 55 to 60 percent as long as body, 20 to 25 percent longer than pereopod 5. Bases of pereopods 5–7 broader proximally than distally; posterior margins slightly convex; distoposterior lobes poorly developed, bluntly rounded. Dactyls of pereopods 6 and 7 relatively short, about one-fourth the length of corresponding propods. Coxal gills on pereopods 2–6. Small sternal blisters present or absent on pereonites 2–7. Brood plates of mature females small and narrow.

Pleonal Plates: Posterior margins nearly straight, plate 1 with 2 setae, plates 2 and 3 with 1 seta each; posterior corners small, rounded; ventral margins of plate 2 with 5 spines, that of plate 3 with 4 spines. Uropod 1: inner ramus equal in length to outer ramus, about two-thirds the length of peduncle, armed with 11 spines; outer ramus with 8 or 9 spines; peduncle with 12 spines. Uropod 2: inner ramus longer than outer ramus, equal in length to peduncle, armed with 11 spines; outer ramus with 8 spines; peduncle with 5 spines. Uropod 3: ramus rather broad, about one-half the length of peduncle, with 4 or 5 apical spines. Telson nearly as broad as long; apical margin with small, V-shaped notch; apical lobes with 6 spines each.

MALE.—Differing from the female as follows: Antenna 1, 50 percent as long as body, 40 percent longer than antenna 2; primary flagellum with 16 segments. Antenna 2, flagellum with 7 segments. Gnathopod 1, palm of propod with double row of 5 spine teeth. Gnathopodal propod 2 less than one-half larger than 1st propod; palm oblique, nearly straight, armed with double row of 6 spine teeth plus 2 additional spine teeth on outside; posterior angle with 1 long spine tooth and 1 seta on outside, 1 shorter spine tooth on inside; posterior margin about two-thirds length of palm, with row of several setae just below defining angle and 1 set of 2 long setae about one-half the distance to base of propod; medial setae mostly singly inserted. Coxal plate of gnathopod 2 with 5 marginal setae. Pereopods 5–7 with few less spines; pereopod 6 a little longer than pereopod 7, 50 percent as long as body, 15 to 20 percent longer than pereopod 5. Sternal blisters not present in material examined. Uropods 1 and 2 with 6 or 7 fewer spines each. Peduncular process of uropod 1 not serrate distally.

VARIATION.—The size of gnathopodal propod 2 varies from 2 to 3 times the size of gnathopodal propod 1 in the female, apparently increasing allometrically in older (and larger) animals. Sternal blisters were not present on females collected from Shaws and Soldier Creek caves.

TYPE-LOCALITY.—Cave of the Catacombs, Mother Lode cave region, Calaveras County, California. A specific location, description, and map of this cave were published by Halliday (1962). The type-series was collected from a lake of fluctuating water in August 1963.

DISTRIBUTION AND ECOLOGY.—This species is known from five caves in central Calaveras County and one cave about 16 miles to the north in Amador County. All of these caves are formed in Middle Paleozoic limestones or marble of the Calaveras formation and are situated along tributaries draining west to the San Joaquin River. According to R. E. Graham (in litt.), most of these caves are developed in isolated lenses of steeply dipping or near vertically bedded limestone and the amount of cave interconnectivity is generally very low.

Most of the animals were found in pools or “lakes,” some of which fluctuate seasonally or with precipitation. Out of 53 specimens studied, 43 were females, 3 were males, and 15 were newly hatched young (about 1.5 mm long). Samples were available from the months of February, May, June, August, and September, and all but the February sample (1 specimen) contained sexually mature females with setose brood plates. The May sample from Cave of the Quills contained 1 female with 8 newly hatched young in the brood pouch and an August sample from the Cave of the Catacombs contained 7 free, newly hatched young. These data indicate that S. grahami reproduces at least during the spring and summer.

ETYMOLOGY.—It is a pleasure to name this species in honor of Dr. Richard E. Graham, a pioneer in the biological study of California caves, who collected most of the specimens of this species and furnished valuable observations on its ecology.