Stygobromus mysticus Holsinger 1974

Stygobromus mysticus

MATERIAL EXAMINED.—CALIFORNIA. Siskiyou Co.: subterranean habitat at Greenview, holotype female (USNM 142794) and 24 paratypes (USNM 142795), W. E. Barrett (date of collection unknown).

DIAGNOSIS.—A rather unique, medium-sized subterranean species, probably distantly related to species of the hubbsi group and distinguished by proportionately small gnathopodal propods; deep coxal plates, especially plate 4, which is also broadly expanded; broadly expanded bases of pereopods 5–7 with convex posterior margins and large, rounded distoposterior lobes; narrow outer rami of uropods 1 and 2; and long, distally tapering telson with rather short apical spines. Largest females, 8.0 mm; male unknown.

DESCRIPTION.—Antenna 1: about 45 percent as long as body, 55 to 60 percent longer than antenna 2; primary flagellum with 15 or 16 segments. Antenna 2: peduncular segments 4 and 5 with a few spines and stiff setae; flagellum with 6 or 7 segments. Mandibles subequal; spine row with 7 spines; palpal segment 2 with 2 long setae; palpal segment 3 with row of short setae on inner margin and 4 long setae apically. Maxilla 1: inner plate with 9 or 10 apical, plumose setae; outer plate with 4 slender spines and 1 stiff seta on apex. Maxilla 2: inner plate with oblique row of 9 or 10 plumose setae on inner margin. Maxilliped: apex of inner plate with 1 bladelike spine, 3 plumose spines and 3 or 4 setae, inner margin with 6 plumose setae; outer plate with 1 bladelike spine and about 6 stiff setae apically. Lower lip without inner lobes.

Gnathopodal Propod 1: Palm not oblique, nearly straight, armed with double row of 4 small spine teeth; posterior angle with 3 long spine teeth on outside, 5 shorter spine teeth on inside; posterior margin without setae; medial setae singly inserted. Coxal plate of gnathopod 1 longer than broad, with 4 marginal setae. Gnathopodal propod 2 as broad as, but about one-fourth longer than, 1st propod; palm slightly convex, armed with double row of 6 spine teeth; posterior angle defined by 1 long spine tooth and several long setae on outside, 1 short spine tooth on inside; posterior margin about as long as palm, with 3 sets of 3 or 4 long setae each; medial setae mostly singly inserted; dactyl nail and accessory spine moderately long. Coxal plates of gnathopod 2 and pereopod 3 rather deep, about 30 percent longer than broad, with 4 or 5 marginal setae each; coxal plate of pereopod 4 broad and deep, reaching about two-thirds the length of segment 2, with 9 or 10 short setae marginally. Pereopod 6 a little longer than pereopod 7, about 40 percent as long as body, about 20 percent longer than pereopod 5. Bases of pereopods 5–7 broadly expanded; posterior margins convex; distoposterior lobes large, bluntly rounded. Dactyls of pereopods 6 and 7 about one-third the length of corresponding propods. Coxal gills on pereopods 2–6. Brood plates of mature females small and narrow.

Pleonal Plates: Posterior margins nearly straight; posterior corners of plates 1 and 3 tiny but distinct, that of plate 2 rounded and indistinct; ventral margins of plates 2 and 3 with 3 spines each. Uropod 1: inner ramus a little longer than outer ramus, about two-thirds the length of peduncle, armed with 7 spines; outer ramus with 5 spines; peduncle with 6 spines. Uropod 2: inner ramus about one-fourth longer than outer ramus, equal in length to peduncle, armed with 7 spines; outer ramus with 4 or 5 spines; peduncle with 5 spines. Uropod 3: ramus about one-third the length of peduncle, with 4 rather short, apical spines. Telson nearly twice as long as broad, tapering distally; apical margin with very shallow notch; apical lobes with 4 short spines each.

TYPE-LOCALITY.—A subterranean habitat at Greenview, Siskiyou County, California. The habitat is possibly a well, but this was not specified on the collection label. Greenview is located in the Klamath Mountains and the area surrounding the town is underlain by both metamorphic rocks of Paleozoic age and more recent deposits of Quaternary age.

DISTRIBUTION AND ECOLOGY.—This species is known only from its type-locality. Two of the larger females in the sample measured 7.5 to 8.0 mm and had setose brood plates.

ETYMOLOGY.—The specific name is from the Latin mysticus, meaning “secret,” so named because of the secretive nature of this species, both in regard to its habitat and its relationship to other western species of the genus Stygobromus.