Closely related to Tellimya ferruginosa . Shell small, fragile, equivalve and moderately convex. Outline oblong-ovate. Subequilateral. Beaks are subcentral. Antero-dorsal margin slightly excurved; antero-ventral portion slightly pointed. Hinge teeth feeble (M. tenella-hinge). Resilifer submarginal, forming a very acute angle with the posterior-dorsal edge of the shell. Surface almost smooth, with fine and dense growth-lines and a few stronger ones at irregular intervals, with faint microscopic radiating striae. Periostracum thin polished film. Interior is smooth, mat or slightly polished.
Up to 4.3 x 2.8 mm.
Transparent bluish-white in living and fresh specimens, opaque and yellowish-white in preserved ones.
Soft parts much like in Tellimya ferruginosa : one large siphonal tentacle above, and another one below, the orifice of the exhalant siphon. However, there are only a few scattered papillae along the ventral part of the middle fold of the mantle, not numerous and densely places ones as in T. ferruginosa .
Lives at moderate depths in soft bottoms.
Scandinavian shelf from northern Norway to Øresund (Distr. M. tenella).