Egg structure of some vertiginid species (Gastropoda: pulmonata: Vertiginidae)

Eggs of species of the genus Vertigo: angustior, antivertigo, moulinsiana, pusilla, pygmaea, ronnebyensis and substriata are flattened-sphaerical (lenticular), gelatinous and nearly colourless. The eggs of V. angustior, V. pygmaea and V. moulinsiana have 3 envelopes: external, gelatinous and internal. In V. angustior the external envelope bears sparse granules while in V. moulinsiana and V. pygmaea it is smooth. The eggs of V. antivertigo, V. pusilla, V. ronnebyensis and V. substriata are additionally surrounded with a mucus cover of variable thickness and density. The mean egg size (diameter in mm) is: pygmaea – 0.54, angustior – 0.59, pusilla – 0.63, substriata – 0.64, antivertigo – 0.65, ronnebyensis – 0.70, moulinsiana – 0.74. The smallest egg (0.42 mm) was laid by V. pygmaea, the largest (0.87 mm) by V. moulinsiana. Eggs of Truncatellina cylindrica are spherical or slightly oval, with a strongly calcified external envelope, and are 0.52-0.58 mm in diameter. Eggs of Columella edentula are probably calcified, flattened-oval, 0.64-0.66 × 0.69-0.71 mm, with their external envelope rugose.