Rimet & Couté in Rimet et al. 2010 Category: Monoraphid
BASIONYM: Achnanthidium druartii Rimet & Couté in Rimet et al. 2010
Contributor: Marina Potapova - August 2011
Length Range: 14-25 µm
Width Range: 4.1-5.3 µm
Striae in 10 µm: 15-20 in 10 µm in the center valve, 40-50 in 10 µm at the ends of raphe valve, 25-35 in 10 µm at the ends of rapheless valve
Valves are linear-lanceolate to lanceolate with subrostrate ends. The raphe valve possesses a linear axial area, which widens slightly in the middle portion of the valve. The terminal raphe fissures are hooked towards the same side of the valve. Externally, the central raphe ends are teardrop-shaped. Internally, the central raphe ends curve to opposite sides. The rapheless valve has a narrow, linear axial area, widening slightly in the middle. Striae are very slightly radiate throughout both valves. The external openings of the areolae are transapically elongated, appearing as narrow slits. Each stria in the middle part of the valve is composed of 6-7 areolae. Very short marginal striae are often present in the middle portion of the valve.
Basionym: Achnanthidium druartii
Author: Rimet & Couté in Rimet et al. 2010
Length Range: 12-29 µm
Width Range: 3.9-5.8 µm
Striae in 10 µm: 15-22 in the center valve, 40-50 at the ends
Valves lanceolate with slightly subrostrate ends never capitate. Valve length 12-29 μm (average 21 μm), valve width 3.9-5.8 μm (average 5 μm). Raphid valve is presenting proximal ends in the shape of tapered drops in external view which are distant by about 0.8 μm. Central endings in internal view are short and curved to opposite sides. The raphe sternum is larger in the middle of the valve than in the extremities. Rapheless valve is convex, with narrow straight sternum very slightly enlarged in the middle. Striae are very weakly radiate throughout on both valves. Occasionally there are short striae inserted near the middle of the valve. For both valves, stria density is 15-22 in 10 μm (average 18) at the valve center and about 40-50 in 10 μm near the apices. Striae in the middle part of the valve are composed of 6 to 7 areolae, whereas striae in the extremities are only composed of 3 to 4 areolae. External foramina of areola are round to slightly elongated. Internal foramina of areola are closed by a rectangular hymen. The internal foramina are forming lines inside a shallow depression and foramina are separated from each other except near the apex where they are coalescent. On both valves, the rows of areola are interrupted at the apex.
Rimet, F., Couté, A., Piuz, A., Berthon, V. and Druart, J.C. . (2010). Achnanthidium druartii sp. nov. (Achnanthales, Bacillariophyta), a new species invading European rivers. Vie et Milieu - Life and Environment 60(3):185-195.
Achnanthidium druartii has been reported in North America only recently from rivers in Kentucky and Virginia (Potapova, unpublished). This species is considered invasive in France (Rimet et al. 2010). It is not clear in either location, however, if the species was misidentified in the past and if it has a broader distribution.