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A Parabathynellid Crustacean - Pacificabathynella stanfordi

Native Species

Global Rank: GNR
State Rank: SNR

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General Description
[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. stanfordi: Male body length 0.53-1.02 mm, female body length 0.51-0.94 mm; body form not very elongated, almost cylindrical, approximately 13 times long as wide; pleotelson with 1 barbed dorsal seta on either side, shorter than furcal rami. Antennule and antenna with 7 segments, antennule slightly shorter than antenna; epipod of thoracopods I and II absent; exopod of thoracopods I-VII with 5 setae; female thoracopod VIII with 1 plumose seta on coxa, 1 smooth seta on basipod, 2 smooth setae on exopod and 2 smooth setae on endopod; male thoracopod VIII with 1 seta on basipod, 1 seta on endopod, crest of basipod very pronounced; 1/6 setae on pleopod; endopod of uropod with 6 spines, exopod of uropod with 7 setae; first spine on furca 1.3 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 March, April, May, July, and November; immatures present in late March (Camacho et al. 2009; Camacho et al. 2016). Adults probably active throughout the year.

Diagnostic Characteristics
The smallest species in the genus. Thoracopods I-VII with 5 setae (not 6 as with P. kalispellensis and P. ruthae); second segment of pleopod with 6 setae (not 7); uropod with 5 spines on endopod (not 4, 6, or 8) and 7 setae on exopod (not 8 or 9).

Range Comments
Montana endemic: reported from two localities (nine wells) on the Flathead River floodplain (Kalispell Aquifer) and Nyack floodplain (Nyack Aquifer) in Flathead County (Camacho et al. 2009), at about 1000-1200 m elevation. Specific well depths not reported but largely between 1 and 12 m.

Observations in Montana Natural Heritage Program Database
Number of Observations: 9

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Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Not described. Likely moves through hyporheic groundwater system.

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

Food Habits
Not described.

Reproductive Characteristics
Not described.

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Citation for data on this website:
A Parabathynellid Crustacean — Pacificabathynella stanfordi.  Montana Field Guide.  .  Retrieved on , from