Family: Pseudostome terminal, of variable shape.
Genus: Pseudostome lacks lobed collar; test round or oval in cross-section; pseudostome relatively large, with or lacking a collar (Illustrated Guide, 1985).
Species: 45-50 μm long for small varieties, 100-600 μm long for large varieties; 25-30 μm wide (test diam.), small; 70-350 μm wide, large; test flask-shaped, base round or polygonal, narrow tapered neck; chitinoid, large imbedded quartz grains; Symbiont, green alga (Kudo, 1966).

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Test L/W less than 1.5
D. pyriformis ? 410 x 260 μm L/W=1.6 P/W=0.25 Shimo-no-koike Shiga highland Nagano, 2005	D. pyriformis ? 348 x 214 μm L/W=1.6 P/W=0.31 Hasu-ike Shiga highland Nagano, 2005	D. pyriformis ? 290 x 220 μm L/W=1.3 P/W=0.32 Tanohara marsh Shiga highland Nagano, 2006	D. pyriformis ? 310 x 206 μm L/W=1.5 P/W=0.29 Shimo-no-koike Shiga highland Nagano, 2005
D. pyriformis ? 240 x 164 μm L/W=1.5 P/W=0.30 Numa-no-hara m. Madarao highland Niigata, 2005	D. pyriformis ? 220 x 150 μm L/W=1.5 P/W=0.27 Imori pond Myoko highland Niigata, 2004	D. pyriformis ? 175 x 140 μm L/W=1.3 P/W=0.34 Tanohara marsh Shiga highland Nagano, 2004	D. pyriformis ? 98 x 74 μm L/W=1.3 P/W=0.24 Japan, 199?
D. pyriformis or D. oblonga ? 90 x 60 μm L/W=1.5 P/W=0.41 Univ. A.V.M. Obihiro Hokkaido, 2005
Test L/W more than 1.5
D. pyriformis 360 x 230 μm L/W=1.6 Iyari marsh Omachi Nagano, 2008 Movies	D. pyriformis ? 280 x 166 μm L/W=1.7 P/W=0.33 near Imori pond Myoko highland Niigata, 2004	D. pyriformis 206 x 119 μm L/W=1.7 P/W=0.32 Japan, 199?	D. pyriformis 145 x 80 μm L/W=1.8 P/W=0.44 Kisuge konuma Shimogo Fukushima, 2005
D. pyriformis ? or D. oblonga ? 164 x 80 μm L/W=2.1 P/W=0.38 Hiroshima, 1998 Movies	D. pyriformis or D. oblonga ? μm L/W=1.6 P/W=0.39 Japan, 199?
Intermediate types
D. pyriformis or D. oblonga ? 190 x 100 μm L/W=1.9 P/W=0.30 Suiren-numa Hakkoda mountain Aomori, 2005	D. pyriformis or D. oblonga ? 178 x 100 μm L/W=1.8 P/W=0.33 Aizu Recreation p. Aizuwakamatsu Fukushima, 2005	D. pyriformis or D. oblonga ? or D. lanceolata ? 170 x 90 μm L/W=1.9 P/W=0.33 Ichinose-enchi Norikura highland Nagano, 2005	D. pyriformis or D. oblonga ? 88 x 42 μm L/W=2.1 P/W=0.38 Japan, 199?
D. pyriformis ? or Nebela sp. ? 205 x 110 μm L/W=1.9 P/W=0.38 Gozaisho marsh Hachimantai Iwate, 2005

Similar species -->> D. oblonga;

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