On the development, habitat selection and taxonomy of Helix (Jacosta) siphnica Kobelt (Gastropoda, Helicellinae)

The environmental factors affecting the distribution, variation, and development and taxonomy of Helix (Jacosta) siphnica Kobelt, 1883, an endemic landsnail of Siphnos Island (Cyclades, Greece), are examined.
Two types of populations can be distinguished due to different strategies of shell development. In the first, and more frequent, type, the keeled and depressed juvenile shells, become rounded in the later developmental stages. In the second type, in all developmental stages, only keeled shells are found. In this study changes in the allometric relationships of shell height, shell diameter and whorls are correlated with the development of the genital system and changes in habitat selection. The keeled forms are found in drier and more stony environments. The degradation of the forests to dry maquis and frygana and desertification in the Aegean insular ecosystems are probably connected with the development of keeled forms. Keeled populations of Trochoidea siphnica are regarded as an example of neoteny leading to paedomorphosis by retardation.