Stygobromus elliotti Holsinger 1974

Stygobromus elliotti

MATERIAL EXAMINED.—WASHINGTON. Skamania Co.: Deadhorse Cave, holotype female (USNM 142779) and 8 paratypes (JRH), W. R. Elliott et al., 22 Aug. 1972; 6 paratypes (BBM), F. G. Howarth and Lynn M. Ferguson, 14 Aug. 1972; other collections (in BBM) from Skamania Co. as follows: Upper Falls Creek Cave system, 1 female, F. G. Howarth and L. Nieuwenhuis, 24 Aug. 1972; Little Red River Cave, 7 females, Howarth and Nieuwenhuis, 26 Aug. 1972.

DIAGNOSIS.—A comparatively large cavernicolous species easily differentiated from other members of the hubbsi group and distinguished by the long and heavily setose palpal segment 2 of the maxilliped; 8 serrate spines on apex of inner plate of maxilla 1; broadly rounded outer lobes and short lateral processes of the lower lip; proportionately small gnathopodal propod of the male; typically uneven posterior margins of the bases of pereopods 5–7; presence or absence of sternal blisters; and frequently unnotched apical margin of the telson. Largest females, 9.5 mm; largest males, 7.0 mm.

FEMALE.—Antenna 1: 55 to 60 percent as long as body, 55 to 60 percent longer than antenna 2; primary flagellum with 19 to 23 segments. Antenna 2: peduncular segment 3 with 7 slender spines, peduncular segments 4 and 5 with numerous slender spines and long setae marginally; flagellum with 7 or 8 segments. Mandibles subequal; spine row with 9 spines; palpal segment 2 with 15 setae on inner margin, segment 3 with row of short setae on inner margin and 5 long setae apically. Maxilla 1: inner plate with 9 apical, plumose setae; outer plate with 8 apical, serrate spines; palp with 7 spines and 6 setae apically and subapically. Maxilla 2: inner plate with oblique row of 10 plumose setae on inner margin, numerous short setae on apex; outer plate with numerous long, apical setae. Maxilliped: inner plate with 3 bladelike spines, 3 plumose spines and 3 setae apically and 5 plumose spines on inner margin; outer plate with 2 bladelike spines and 9 setae apically and double row of short setae on inner margin; segment 2 of palp with numerous long setae on inner margin. Lower lip with broad outer lobes and bluntly rounded lateral processes, inner lobes lacking.

Gnathopodal Propod 1: Palm long, oblique, straight, armed with double row of about 8 spine teeth; posterior angle with 5 spine teeth and 2 setae on outside, 7 spine teeth on inside; posterior margin rather short, without setae; medial setae singly inserted; dactyl not reaching to defining angle. Coxal plate of gnathopod 1 longer than broad, with 2 short, marginal setae. Gnathopodal propod 2: palm long, oblique, slightly concave, armed with double row of 12 or 13 spine teeth; posterior angle with 2 long spine teeth and 2 sets of long setae on outside, 3 long spine teeth on inside; posterior margin with 1 set of 3 setae; medial setae mostly singly inserted; dactyl rather long and curved, nail short. Coxal plates of gnathopod 2 and pereopods 3 and 4 about as broad as long, plates 2 and 3 with 5 marginal setae each, plate 4 with 8 marginal setae. Pereopod 6 a little longer than pereopod 7, 50 to 55 percent as long as body, about 20 percent longer than pereopod 5. Bases of pereopods 5–7 not much broader proximally than distally; posterior margins nearly straight or slightly irregular, with 12 setae on pereopod 7 and 16 setae each on pereopods 5 and 6; distoposterior lobes distinct, bluntly rounded. Dactyls of pereopods 6 and 7 about one-third the length of corresponding propods. Coxal gills present on pereopods 2–6. Small sternal blisters sometimes present ventrally on pereonites 2–7, more obvious on pereonites 5–7. Brood plates of mature females small and narrow.

Pleonal Plates: Posterior margins nearly straight to slightly convex; posterior corners poorly developed, rounded; ventral margin of plate 2 with 2 spines, that of plate 3 with 3 spines. Uropod 1: inner ramus slightly longer than outer ramus, about two-thirds the length of peduncle, armed with 10 to 12 spines; outer ramus with 10 spines; peduncle with 10 or 11 spines. Uropod 2: inner ramus longer than outer ramus, subequal in length to peduncle, armed with 12 to 16 spines; outer ramus with 6 or 7 spines; peduncle with 4 spines. Uropod 3: ramus about 40 percent as long as peduncle, armed with 3 to 5 apical spines. Telson longer than broad; apical margin often entire, sometimes slightly emarginate, armed with 12 to 16 spines.

MALE.—Differing from the female as follows: Gnathopodal propod 1 with fewer spine teeth on palm. Gnathopodal propod 2 proportionately much smaller, not much larger than 1st propod; palm not very oblique, slightly convex, armed with double row of 4 spine teeth; posterior angle with 3 long spine teeth and several long setae on outside, 3 shorter spine teeth on inside; posterior margin with 5 or 6 long setae. Pereopods 5–7 with few less spines. Uropod 1: inner ramus slightly longer than outer ramus, about two-thirds the length of peduncle, armed with 8 spines; outer ramus with 7 spines; peduncle with 7 spines and distal process. Uropod 2: inner ramus longer than outer ramus, equal in length to peduncle, armed with 10 spines; outer ramus with 5 spines; peduncle with 2 spines. Telson with 10 or 11 apical spines.

VARIATION.—Slight variation in the structure and number of spines of the telson, the number of spines on uropod 3 and the presence or absence of sternal blisters was noted. A few females in the samples from both Deadhorse and Little Red River caves had a tiny notch in the apical margin of the telson. Most of the females from Little Red River Cave had 3 apical spines on the ramus of uropod 3 and 14 to 16 apical spines on the telson, while, in comparison, most of the females from Deadhorse Cave had 4 or 5 apical spines on uropod 3 and 12 to 14 apical spines on the telson. The presence or absence of sternal blisters was variable in each population.

TYPE-LOCALITY.—Deadhorse Cave, 7 miles northwest of Trout Lake, Skamania County, Washington. The type-locality is a relatively large, complex lava cave formed in the Mount Adams pahoehoe lava flow. The type-series was collected from a stream and stream pools (water temperature = 5°C) in association with an undescribed species of troglobitic isopod (Asellus) and eyed planarians of the family Dendrocoelidae.

DISTRIBUTION AND ECOLOGY.—This species is recorded from three lava caves in Skamania County. The specimens from Upper Falls Creek and Little Red River caves were collected from streams and pools (water temperature = 5°C). Upper Falls Creek Cave, located about 15 miles south-southwest of Deadhorse Cave, is also developed in pahoehoe lava of the Mount Adams flow. Little Red River Cave is located about 25 miles west-northwest of Deadhorse Cave and is developed in pahoehoe lava of the Mount St. Helens flow. Some of the females, ranging in size from 5.0 to 9.5 mm, had setose brood plates, and one female (8.0 mm) from Little Red River Cave was ovigerous with 12 embryos in the brood pouch. Out of the 23 specimens studied, only two were males.

ETYMOLOGY.—It is a pleasure to name this species in honor of its collector, William R. Elliott.