Stygobromus puteanus Holsinger 1974

Stygobromus puteanus

MATERIAL EXAMINED.—MONTANA. Gallatin Co.: well near Three Forks, holotype female (USNM 142799) and 3 paratypes (USNM 142800), C. A. Tryon, Jr., Feb. 1939.

DIAGNOSIS.—A medium-sized subterranean species apparently related to S. tritus but distinguished from that species by the straight to slightly convex palms of the gnathopodal propods; broader bases of pereopods 5–7; more spines on uropods 1 and 2; longer apical spines on uropod 3; and proportionately longer and more spinose telson with 16 apical spines (of which 4 are very long and slender). Largest females, 6.5 mm; male unknown.

DESCRIPTION.—Antenna 1, 45 to 50 percent as long as body, about 40 percent longer than antenna 2; primary flagellum with 19 or 20 segments. Antenna 2, flagellum with 5 segments. Mouthparts similar to those of S. hubbsi. Gnathopod 1: propod palm slightly convex, armed with double row of about 5 small spine teeth; posterior angle distinct, with 1 long and 2 short spine teeth on outside, 5 short spine teeth on inside; posterior margin without setae; medial setae few in number, singly inserted; dactyl nail rather long. Coxal plate of gnathopod 1 about twice as long as broad, with 3 marginal setae. Gnathopod 2: propod up to one-third larger than 1st propod; palm oblique, nearly straight, armed with double row of 8 or 9 spine teeth; posterior angle defined by 1 long, curved spine tooth and 3 long setae on outside, 1 or 2 small spine teeth on inside; posterior margin convex, with 2 sets of long setae; inferior medial setae singly inserted, superior medial setae singly and doubly inserted; dactyl rather long, slightly curved, nail moderately long. Coxal plates of gnathopod 2 and pereopod 3 rather shallow, about as broad as long; plate 2 with 3 marginal setae, plate 3 with 6 marginal setae. Coxal plate of pereopod 4 broader than long, with 8 marginal setae.

Pereopod 6, 45 to 50 percent as long as body, slightly longer than pereopod 7, about 25 percent longer than pereopod 5. Bases of pereopods 5–7 rather narrow, slightly broader proximally than distally; posterior margins with 8 to 10 setae; distoposterior corners small, poorly defined. Dactyls of pereopods 6 and 7 nearly 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 convex; posterior corner of plate 1 rounded, corners of plates 2 and 3 indistinct; ventral margins of plates 2 and 3 with 3 spines each. Uropod 1: inner ramus slightly longer than outer ramus, about 60 percent as long as peduncle, armed with 13 or 14 spines, many of which are long and slender; outer ramus with 9 spines; peduncle with 25 spines. Uropod 2: inner ramus nearly twice as large as outer ramus, about 70 percent as long as peduncle, armed with 16 mostly elongate spines; outer ramus with 6 spines; peduncle with 12 spines. Uropod 3: ramus proportionately short, only about one-fourth the length of peduncle, armed with 3 long, apical spines. Telson a little longer than broad; apical margin with very tiny notch; apical lobes with 8 unequal spines each.

TYPE-LOCALITY.—A driven well, 80 feet deep, near Three Forks, Gallatin County, Montana. The exact location of this well was not specified by the collector, therefore it is impossible to determine the geological formation in which it occurs. Three Forks is situated in the Northern Rocky Mountains and the area surrounding the town is underlain by both sedimentary rocks of Early Paleozoic age and more recent deposits of Tertiary and Quaternary age.

DISTRIBUTION AND ECOLOGY.—This species is known only from its type-locality. The type-series contained four females, ranging in size from 6.0 to 6.5 mm. All four specimens had setose brood plates and were apparently sexually mature.

ETYMOLOGY.—The specific name is from the Latin, meaning “of a well.”