Bembidion saturatum, CASEY, 1918

Sproul, John S. & Maddison, David R., 2018, Cryptic species in the mountaintops: species delimitation and taxonomy of the Bembidion breve species group (Coleoptera: Carabidae) aided by genomic architecture of a century-old type specimen, Zoological Journal of the Linnean Society 183, pp. 556-583 : 577-578

BEMBIDION SATURATUM CASEY

( FIGS 2A, 9A, B, 10D, 11D, 16A)

Bembidion saturatum Casey, 1918: 24 . Lectotype female, designated by Lindroth (1975: 117), in USNM, labelled ‘Placer co. Cal.’ [white paper], ‘CASEY bequest 1925’ [white paper], ‘TYPE USNM 36831’ [red paper], ‘saturata Csy.’ [white paper, handwritten], ‘ LECTOTYPE saturatum Csy. By C.H. Lindroth’ [white paper, partly handwritten]. Type locality: Placer Co., California. Examined, including DNA sequences.

Nomenclatural notes: This is the species referred to as ‘ Bembidion “University Peak”’ in Sproul & Maddison (2017). Extracted DNA is deposited at the USNM and associated with the GUID of the type specimen: ark:/65665/380c4cce2-3007-4a2d-9d40-5865c9760b 4f.

Diagnosis: This small-bodied convex species has a broad pronotum and stout appearance ( Fig. 2A). Forebody and hindbody dark brown, some specimens with an aeneous reflection. Pronotum very broad basally with hind angles near 90°; lateral explanation broad ( Fig. 11D), laterobasal carina somewhat weak as the basal fovea beside it is quite shallow, and thus the carina does not stand out so prominently, although carina may still extend far anteriorly. Elytra long relative to length of pronotum; tapered apically in some specimens; dorsal punctures weakly foveate ( Fig. 2A). Microsculpture meshes strongly etched in females and moderately etched in males (except for populations in eastern Oregon and Nevada where microsculpture is notably weakened). Male genitalia with long sinuate flagellum ( Figs 9A, B, 10D); sclerite ‘St’ either lacking ( Fig. 9A), or with a hint of sclerotization in the position of sclerite ‘St’ ( Fig. 9B).

Comparison with similar species: Most easily confused with B. vulcanix and B. geopearlis , from which it is extremely difficult to separate using only external structures. It is most easily distinguished using characters in the male genitalia and geography. It is separated from both by lacking sclerite ‘St’ (but see note on ‘Geographic variation’ below), and by having a southern and southeastern distribution ( Fig. 16). May also be confused with B. breve , from which it is distinguished by a slightly larger body with more parallel-sided elytra, weakly foveate dorsal punctures, and a longer, more sinuate flagellum of the male genitalia.

Geographic distribution: From Washington south to the southern Sierra Nevada, east to the Ruby Mountains in Nevada and Steens Mountains in Oregon ( Fig. 16A) .

Habitat: A variety of damp environments at or below the tree line including damp meadows, along lakeshores or small creeks, or on open alpine slopes below patches of melting snow.

Geographic variation: Populations from the Steens Mountains in eastern Oregon and the Ruby Mountains in Nevada (the ‘eastern form’) are smaller-bodied, shinier and more black than dark brown, with slight sclerotization in the position of sclerite ‘St’ evident (e.g. Fig. 9B), but not nearly so expanded as in B. geopearlis ( Figs 9C, D, 10E) or B. vulcanix ( Figs 9E, F, 10F). A slight patch of sclerotization has also been observed occasionally in individuals from California ( Fig. 9B).