The ruler is in millimeters.
This species has so far been found only at a few disjunct locations in western Turkey. The specimens pictured above are from the vicinity of Manisa. Neubert published a drawing of the genitalia of a specimen from near Bursa1.
As in most clausiliid snails, there are several folds and lamellae in the aperture of the shell of this species and when the snail is fully withdrawn into its shell, the opening in the back of the aperture is blocked by a movable plate, the clausilium. Idyla bicristata has a so-called G type (Graciliaria type) organization of its clausilium and the associated lamellae.
Aperture of the shell of Idyla bicristata with the palatal wall removed; c: columellaris, cm: clausilium, p: parietalis, sc: subcolumellaris. The clausilium is in its closed position.
The evolution of the clausilium in the Clausiliidae is the subject of ongoing research. In future posts I will return to these interesting snails.
1. Neubert, E. 1995. Note on some genera of Clausiliidae from Turkey.
Zoology in the Middle East 11:101-108.