Atomaria ephippiata - dorsal habitus.
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Atomaria ephippiata - dorsal habitus. |
The genus Atomaria is one of 8 genera in the family Cryptophagidae, the silken fungus beetles, found in Atlantic Canada. Atomaria is the only genus in the subfamily Atomariinae LeConte, 1861 found in this region (although the Palearctic Ephistemus globulus (Paykull) is recorded from Ontario. They are small (1.0-2.0 mm), somewhat shiny, oval-oblong, sparsely pubescent beetles typically found in leaf litter, grass litter and in decaying vegetation and in habitats which promote mycelial fungal growth.
Members of this genus are divided into two subgenera, Atomaria Stephens, 1829 and Anchicera Thomson, 1863. Leschen and Skelley (2002) record 10 species from North America (9 described; 1 undescribed) and note that the genus is in need of revision since the last comprehensive treatment in North America was Casey (1900). Nearctica.com records 71 specific names for the Nearctic region, however, as noted, the genus is in great need of revision and many probably represent unrevised names in need of synonymization.
Majka and Johnson are in the process of surveying and revising the genus in Atlantic Canada, however, in the interim, below are dorsal habitus photos along with average, length, widths (at widest-point of the elytra), and width/length ratios. Also a provisional key to the ten species found in Atlantic Canada.
Key to Atlantic Provinces species of Atomaria
- 1. Antennae close basally, separated from each other by a distance not greater than their distance from eyes; antennomere 1 much longer than 2, obconnical; habitus elongate, parallel; width/length ration < 0.35 - subgenus Atomaria Stephens ---- 9
- -- Antennae less close basally, more distant from each other than their distance from eye; antennomere 1 slightly longer than 2; habitus oval, short, compact; width/length ratio > 0.40 - subgenus Anchicera Thomson ---- 2
- 2(1). Elytra distinctly bicoloured ---- 3
- -- Elytral colouration variable, either concolourous, or gradually paler apically, but not with a distinct bicoloured pattern ---- 4
- 3(2) Elytra testaceus with a prominent piceus crossbar at the mid-point, either interrupted or continuous across suture; pronotum and prosternum piceous. 1.5-1.6 mm. ---- Atomaria ephippiata Zimmerman
- -- Elytra abruptly ferruginous in apical 1/2 to 2/5; pronotum and prosternum (except near coxae) ferruginous. 1.4-1.5 mm. ---- Atomaria distincta Casey
- 4(2). Pronotal margin arcuate, broadest at point near middle; evenly narrowing to base. pronotal base straight or weakly curved; Hind angles obtuse. ---- 5
- -- Lateral margins of pronotum in basal half more or less straight, not evenly arcuate; pronotal base sinuate or slightly bi-lobed,; hind angles more right-angled. ---- 6
- 5(4). Antennomere 1 widening apically, at least 1.5 times as long as width of the antennomere at the apical end; clearly longer than antennomere 2. Habitus narrower, body width (at maximum width of elytra) to length ratio 0.47; pronotum comparatively shorter, pronotum to elytra ratio 0.46. Elytra clearly gradually paler in apical half. 1.3-1.6 mm. ---- Atomaria testacea Stephens
- -- Antennomere 1 not noticeably wider apically; at most 1.3 times as long as width of the antennomere at the apical end; not or a slightly longer than antennomere 2. Habitus broader, body width to length ratio 0.54; pronotum comparatively longer, pronotum to elytra ratio 0.64. Elytra indistinctly gradually paler in apical half. 1.3-1.6 mm. ---- Atomaria apicalis Erichson
- 6(4). Testaceus to ferrugineus in colour; antennal club more distinct; antennomeres 9 and 10 slightly transverse to transverse. ---- 7
- -- Usually dark castaneous throughout, sometimes pronotum darker; antennal club less distinct; antennomeres 9 and 10 frequently quadrate. 1.4-1.7 mm. ---- Atomaria fuscata Schšnherr
- 7(6). Antennomere 1 long, curved, 1.5-2.0 times as long as width of the antennomere at the apical end; much longer than antennomere 2. Lateral elytral margins evenly arcuate from widest point at middle. Body and elytra broad; width/length ratio of elytra 0.82, width/length ratio of body 0.53. Elytral setae somewhat erect and "bristling". 1.3-1.6 mm. ---- Atomaria lewisi Reitter
- -- Antennomere 1 short, straight, not expanded at apex, hardly longer than wide, approximately as long as antennomere 2. Lateral elytral margins almost parallel in basal 3/4, narrowed to apex. Body and elytra narrower; width/length ratio of elytra 0.72, width/length ratio of body 0.50-0.48. Elytral setae short and appressed. ---- 8
- 8(7). Antennomere 2 slender, noticeably narrower than antennomere 1. Body dorso-ventrally flattened, width/length ratio (in lateral view) 0.36. 1.2 mm or less in length. 1.0-1.2 mm. ---- Atomaria pusilla (Paykull)
- -- Antennomere 2 robust, at apex the same width (or almost so) as antennomere 1 at apex. Body dorso-ventrally wider and more robust, width/length ratio (in lateral view) 0.43. 1.2 mm or more in length. 1.2-1.4 mm. ---- Atomaria lederi Johnson
- 9(1). Pronotal base with a strong transverse impression, laterally with several fine and sharp longitudinal ridges; pronotum widest at midpoint, lateral margins parallel to base, hind angles distinct. 1.7-1.9 mm. ---- Atomaria nigrirostris Stephens
- -- Pronotal base without a strong transverse impression with sharp longitudinal ridges; pronotum widest at midpoint, lateral margins evenly arcuate to base, hind angles rounded. 1.5-1.8 mm. ---- Atomaria wollastoni Sharp
Atomaria fauna of Atlantic Canada. Anchicera Thomson, 1863 NB NF NS PE Atomaria apicalis Erichson 1 1 Atomaria distincta Casey 1 1 Atomaria ephippiata Zimmerman 1 1 1 Atomaria fuscata Schönherr 1 1 1 1 Atomaria lederi Johnson 1 Atomaria lewisi Reitter 1 1 Atomaria pusilla Paykull 1 1 1 Atomaria testacea Stephens 1 1 Atomaria Stephens, 1829 Atomaria nigrirostris Stephens 1 1 Atomaria wollastoni Sharp 1
Atomaria apicalis Erichson, 1846
Atomaria distincta Casey, 1900
Atomaria ephippiata Zimmerman, 1869
Atomaria fuscata Schönherr, 1808
Atomaria lederi Johnson, 1970
Atomaria lewisi Reitter, 1877
Atomaria pusilla (Paykull, 1798)
Atomaria testacea Stephens, 1830
Atomaria nigrirostris Stephens, 1830
Atomaria wollastoni Sharp, 1867
All determinations by Colin Johnson; all photographs by Christopher Majka (Nova Scotia Museum).
Mean dimensions of Atomaria species in Atlantic Canada. Anchicera Thomson, 1863 length (mm) width (mm) W/L ratio Atomaria apicalis Erichson 1.2 0.50 0.41 Atomaria distincta Casey 1.4 0.60 0.43 Atomaria ephippiata Zimmerman 1.4 0.65 0.46 Atomaria fuscata Schönherr 1.5 0.70 0.47 Atomaria lederi Johnson 1.4 0.60 0.43 Atomaria lewisi Reitter 1.4 0.65 0.46 Atomaria pusilla Paykull 1.0 0.40 0.40 Atomaria testacea Stephens 1.3 0.60 0.46 Atomaria Stephens, 1829 Atomaria nigrirostris Stephens 1.6 0.50 0.31 Atomaria wollastoni Sharp 1.5 0.50 0.33
References
Casey, T.L. 1900. Revision of the North American Cryptophagidae. Journal of the New York Entomological Society, 8: 75-128.
Downie, N.M. and Arnett, R.H., Jr. 1996. The Beetles of Northeastern North America. Sandhill Crane Press. Gainsville, Florida. 1721 pp.
Johnson, C., Otero, J.C., and Leschen, R.A.B. 2007. Cryptophagidae Kirby, 1837. In: Löbl, I. and Smetana, A. (editors). Catalogue of Palaearctic Coleoptera, Volume 4: Elateroidea, Derontoidea, Bostrichoidea, Lymexyloidea, Cleroidea, Cucujoidea. Apollo Books, Stenstrup, Denmark. pp. 513-531.
Leschen, A.B. and Skelley, P.E. 2002. Cryptophagidae Kirby 1837. In: Arnett, R.H., Jr., Thomas, M.C., Skelley, P.E., and Frank, J.H. (editors). American Beetles, Volume 2: Polyphaga: Scarabaeoidea through Curculionoidea. CRC Press, Boca Raton, USA. pp. 338-342.
(c) All rights reserved. Christopher Majka & Empty Mirrors Press. revised 4 July 2009.