Two shells from the same sample, 310 µm (Naardermeer, Netherlands)
Erugomicula bidens (Penard, 1902)
Basionym: Difflugia bidens Penard, 1902
Diagnosis: Shell ovoid, compressed in cross-section, relatively smooth; fundus usually with 2-3 small spines; pseudostome large, circular, without collar; nucleus finely granulated, large, sometimes with a globular structure inside.
Dimensions: Penard (1902): 250-270 µm long; Nasser et al., (2021): 219 – 341 μm; my measurements: 270-366 µm.
Habitat: I found several specimens in detritus from the bottom of ditches in the nature reserve Naardermeer in the Netherlands (GPS 52.281278 – 5.118853). This species has also been recorded for some other European countries and for Canada.
Remarks: This species has usually two spines, hence the name bidens.
Nucleus, 80 µm in diameter; left: DIC, right: normal illumination
Drawing: Penard in Faune Rhizopodique du Bassin du Léman, 1902
E. bidens, 366 µm, front and side view (Naardermeer, the Netherlands)
Four Difflugia species in one sample; left: E. bidens and right: Difflugia nodosa, Naardermeer, the Netherlands
E. bidens, part of the shell
E. bidens, spine
E. bidens, from the Pénard Collection in Geneva – Photographed by Thierry Arnet, as part of the Pénard project (https://commons.wikimedia.org/w/index.php?curid=40497788)
E. bidens, 315 and 270 µm, Naardermeer, the Netherlands