Montana Field Guide

Stygobromus: without eyes and pigment, subterranean; sexually mature animals range from 2.5-12.0 mm; antenna 1 longer than antenna 2; propod of gnathopod 1 usually longer than second propod; pereopod 6 a little longer than pereopod 7, always longer than pereopod 5; uronites free, not fused, dorsal margins without spines; telson usually longer than broad, apical margin entire or emarginate (but not deeply cleft), armed with spines. The principle diagnostic character of the genus is the uniramus third uropod (U3), in which the ramus is 1-segmented, shorter than the peduncle (sometimes vestigial or absent), and when present is armed with 1 to several short spines (Holsinger 1974; Wang and Holsinger 2001).

S. glacialis: [From Wang and Holsinger 2001] Female. "Antenna 1: 40 percent of body length, 40 percent longer than antenna 2; primary flagellum with 6 segments. Mandibles subequal: spine row with 7-8 plumose spines; palp segment 2 with row of 9 long setae on inner margin; palp segment 3 bearing 2B setae, 9 D setae, and 4 setae E, lacking both A and C setae. Inner lobes of lower lip vestigial or absent. Maxilla 1: inner plate with 7 apical, plumose setae on inner margin. Maxilliped: inner plate with 1 bladderlike spine, 5 plumose spines, 2 naked setae apically, and 3 plumose spines on inner margin; outer plate with setae on inner margin and 3 lightly plumose setae on or near apex" (p. 120). Coxal gills present on pereopds 2-6, absent from 7. Three pairs of long, slender simple lateral sternal gills present on pereonites 5-7, longest on 6 and 7. Telson longer than width, apical margin with small median notch bearing 12 relatively long spines. Largest female 7.0 mm in length, largest male 4.5 mm in length. See Diagnostic Characteristics and Wang and Holsinger (2001) for description of additional body regions.

Limited information. Presumably active throughout the year. Type specimens (females) collected 25 and 27 August 1977; additional individuals collected or observed at known localities on 26 June 2010, 20 August 2000 (males, females, juveniles), 19 September 2010, 27 September 1999 (females), 28 September 2010, 25 November 1980 (female) (Wang and Holsinger 2001; Bodenhamer 2011). No S. glacialis reported at known localities 19-20 February 2010, 25-26 June 2010, 4-5 August 2010, ca. 29 August 1976, 3-7 September 1975, 5-6 September 2009, 15-16 September 2009, 27-28 September 2009, 10-11 November 2010 (Campbell 1975; Campbell et al. 1976; Bodenhamer 2011), even though water present during survey.

"A relatively small to medium-sized cavernicolous species, distinguished from all other species of Stygobromus by the possession of 3 pairs of lateral sternal gills on pereonites 5, 6 and 7; and further distinguished by slender bases of pereopods 5-7, and several setules each on posterior margin of pleonal plates" (Wang and Holsinger 2001:120).

Not described. Likely moves through hyporheic and cavernicolous groundwater and spring systems.

Limited information. Cave streams and pools in limestone and dolomite, hyporheic headwater spring systems (Campbell 1975; Campbell et al. 1976; Campbell et al. 1978; Hendricks 2000; Wang and Holsinger 2001; Bodenhamer 2011).

Not described. Apparently attracted to sample boxes baited with raw beef liver (Bodenhamer 2011).

Limited information. Juveniles present with adult males and females on 20 August, ovigerous females (5.8 mm body length) present 27 September, each with 2 embryos in brood pouch (Wang and Holsinger 2001), although each originally carried 4 embryos (Hendricks pers. obs.); females appear to reach sexual maturity when about 5.5 mm body length.