Montana Field Guide

[From Camacho et al. 2009; Camacho et al. 2016] Genus Pacificabathynella: Male body length 0.53-2.07 mm, female body length 0.51-1.78 mm; antennule with 7 segments, antenna with 7-8 segments; mandible with 2 teeth on incisor process (pars incisiva), pars molaris with 2 bidentated structures; labrum with a small central protuberance at distal edge; epipod of thoracopod I absent, epipod of thoracopod II absent or present; exopod of thoracopods I-VII with 5-6 setae; thoracopods VI and VIII sexually dimorphic. Thoracopod VI of male with 3-segmented endopod, thoracopod VIII of male with 3 lobes around genital opening, basipod prominence present, exopod 1-segmented, endopod 1-segmented; thoracopod VI of female with 4-segmented endopod, thoracopod VIII of female with 1-2 plumose setae on coxa, 1-2 setae on basipod, epipod is present, exopod and endopod 1-segmented, 2 apical setae on exopod, 1-2 apical setae on endopod; sympod of uropod with 6-8 spines, endopod of uropod with 4-8 strong spines along inner margin; furcal rami with 5 spines.

P. kalispellensis: Male body length 0.95-1.47 mm, female body length 0.84-1.46 mm; body form not very elongated, almost cylindrical, approximately 12 times long as wide; pleotelson with 1 barbed dorsal seta on either side, shorter than furcal rami. Antennule and antenna with 7 segments. Antennule shorter than antenna (as long as last 5 antenna segments combined); epipod of thoracopod I absent, present on thoracopod II; exopod of thoracopods I-VII with 6 setae; female thoracopod VIII with 2 plumose setae on coxa, 1 plumose seta on basipod, 3 smooth setae on exopod and 2 barbed setae on endopod; male thoracopod VIII with 1 seta on basipod, 1 seta on endopod, crest of basipod very pronounced; 1/7 setae on pleopod; endopod of uropod with 8 spines, exopod of uropod with 8 setae; first spine on furca 2.3 times longer than second spine and 2 times longer than dorsal spine, size of first spine>dorsal spine>second spine=third spine>fourth spine.

Not described. Adult males and females collected in February, April, and May; juvenile present in late April (Camacho et al. 2009; Camacho et al. 2016). Adults probably active throughout the year.

Antennule 25% shorter than antenna. With a profusion of setae on antenna and thoracopods; setal formula on antenna (0/2/3/12/6/8/5) is unique to the genus, the 4th segment very long with many setae, 5th segment well-developed with many setae (normaly this segment lacks setae). Thoracopod II with an epipod (absent in P. ruthae and P. stanfordi); male thoracopod VIII very large with very pronounced basipod crest; female thoracopod VIII with a very large epipod (3 times length of basipod); the exopod with 3 smooth setae (only 2 smooth setae for P. ruthae and P. stanfordi).

Not described. Likely moves through hyporheic groundwater system.

Hyporheic groundwater aquifers and water wells in alluvial flood plains, interstitial (Camacho et al. 2009).

Not described.

Not described.