Zospeum robustum

Zospeum robustum has an average shell height of ca. 1.6 mm and an average shell width of ca. 1.1 mm. The shell is transparent and has an ovate-conical shape, showing a high variability in shape. It is either smooth or ribbed, sometimes at the uppermost part of the whorl or the entire whorl. The shell possesses between 4.75 and 6 whorls, whereby the last whorl is sometimes expanded. The opening (aperture) is taller than wide. The peristome is roundish, sometimes quite massive, in most cases with a small, straight parietal shield. The shell has a parietalis and a weak columellaris. The columellaris is completely absent in those populations with ribbed shells.^[1]

Zospeum robustum occurs in Croatia in three separate areas:

1) In the caves Budina špilja and Markov ponor in the Lika-Senj county, as well as in Ostrvička špilja and the upper part of the Lukina jama-Trojama cave system.

2) In the caves Tonkovića špilja and Špilja pod Mačkovom dragom in the north of Ogulin.

3) In three caves in and around the Žumberak Mountains: Vrlovka, Pušina jama and Židovske kuće.