Virginia Land Snails
Photo(s): Three views of a Helicodiscus diadema shell, noting the curved processes upon the outer protein coat. Images by Jeffrey C. Nekola ©.
Click photo(s) to enlarge.
Helicodiscus diadema Grimm, 1967
Common name: Shaggy Coil
Width: 3.0-4.5 mm
Height: 1.0-1.5 mm
The shell of Helicodiscus diadema is disk-like, with a flat spire and a wide, shallow umbilicus nearly half the diameter of the shell. The rounded whorls are sculptured with growth wrinkles, intersected by spiral lirae, on which fine, curved “hairs” can be barely seen. Sparkling dew trapped on these hairs led Grimm (1967) to name this species for a diadem, or royal headband. These processes are worn off on older shells.
The final whorl of the shell descends slightly towards the rounded aperture. Near the aperture there are sets of three teeth - two long, radially-oriented teeth on the basal and outer walls, and one cupped tooth on the parietal wall – and there may be two or three sets.
Helicodiscus diadema is found on thinly-wooded hillsides among limestone talus and rubble. It appears to be active at the surface only during damp periods.
While Grimm’s description notes three separate locations for this species, recent work suggests that two of these sites may have been misidentified subfossil shells of other helicodiscids (K.P. Hotopp, J.C. Nekola, T.A. Pearce, pers. obs.). There are no synonyms of H. diadema.
Helicodiscus diadema is an endemic known only from the Falling Spring valley in Bath and Alleghany Counties, Virginia.
NatureServe Global Rank: G1
NatureServe State Rank: S1
Virginia’s wildlife action plan: Tier I
State Status: Endangered
Ken Hotopp, Meegan Winslow 11/2012Range Map