Centropyxis dentata Siemensma, Shimano & Wanner, 2024
Diagnosis: Shell circular, oblong or ovoid when viewed ventrally, with its width sometimes being greater than its length. In ovoid shells, both sides taper slightly towards the anterior lip, sometimes with a slight constriction. In lateral view, the height of the shell is about 2/3 that of the length, the ventral side appears flat. From the dorsal area, the anterior side runs in a convex line to the anterior lip, while the posterior area of the shell has a semicircular contour that curves inward on the ventral side about halfway up the shell’s height and then bends horizontally, forming the posterior lip. In ventral view, the pseudostome looks oval and is strongly eccentrically located. The anterior lip is broad, usually filled with larger mineral particles and with 2-6 relatively large, often triangular, and sharply pointed mineral particles attached to the lip in the ventral plane. Some shells do not have these tooth-like particles and are less densely embedded with xenosomes. The posterior lip varies in width, up to 18 µm wide, but not always present or visible. Shell composed of chitinoid cement embedded with mostly flat mineral particles, giving the shell a dark color or sometimes a yellowish color when the shell is less densely packed with mineral particles. No living specimens have been observed.
Dimensions: Bhutan population: Shell length 130-178 µm (mean 148 µm), width 105-149 µm (mean 130 µm) and L/W ratio 0.92-1.39 (mean 1.14); pseudostome width 62-78 µm.
Habitat: Freshwater.
Geographical distribution: Type locality: Wangdue Phodrang district, Bhutan, GPS 27.4353 N 90.1999 E.
Differential diagnosis. Centropyxis dentata differs from all other described Centropyxis species by the presence of some relatively large mineral particles that protrude like large teeth from the anterior lip. In general shape and size it bears some similarity to C. ecornis (Ehrenberg, 1841) Leidy, 1879, C. orbicularis Deflandre, 1929 and C. janetscheki Laminger, 1971. Centropyxis orbicularis and C. janetscheki also tend to incorporate relatively large mineral particles into the anterior lip, but these particles never protrude from the lip like teeth. In lateral view, the contour of C. orbicularis is hemispherical, which is clearly different from the contour of C. dentata, where the anterior region is slightly convex or straight. Centropyxis orbicularis is also rounded in ventral view, while the shape of C. dentata is rounded to ovoid. In contrast to C. dentata, the posterior part of C. janetscheki is clearly separated from the pseudostome part (“setzt sich bei Dorsalansicht deutlich vom Pseudostomteil ab”). Centropyxis ecornis has no major elements in the anterior lip.
