Isomeria Albers, 1850

Cuezzo, Maria Gabriela, 2006, On a new species of Isomeria Beck and redescription of species of Labyrinthus Beck from South America (Gastropoda: Stylommatophora: Camaenidae), Zootaxa 1221, pp. 1-23 : 16-17

Isomeria Albers, 1850

Type species: Helix oreas Koch, 1844 , by monotypy.

Diagnosis: Shell small to large (18–75 mm) generally globose; shell surface sculpture with wrinkles, granulations and/or malleations; periphery convex to obtusely angulated; umbilicus usually closed or very narrow; lip thick, reflected with aperture subquadrate with few teeth and lamellae, toothless in some species; parietal callus usually thin, sometimes raised edge; parietal wall generally toothless or with small triangular teeth or short lamellae; basal lip with 0–2 denticles, palatal lip having small triangular denticle in most species, rarely with large tooth marked by posterior indentation; presence of special structures such as penial appendages, epiphallic flagellum and/or stimulator­like appendage in vagina­atrium; both vagina and penis with internal hooked denticles. Jaw smooth or with weakly developed plaques.

Distribution: distributed from Sierra Nevada de Santa Marta in northern Colombia, Valle del Cauca, Cordillera Central and Occidental in Colombia south to Cajamarca department in Peru ( Solem 1966; Breure 1984). Isomeria is more abundant in Ecuador at Esmeraldas and in amazonian localities close to Napo River. Its distributional range seems to be more restricted than that of Labyrinthus , further collections will allow to define more precisely the distribution of Isomeria .

Remarks:In the phylogenetic hypothesis proposed for Camaenidae by Cuezzo (2003), the synapomorphies supporting the monophyly of Isomeria were only shell characters. This is probable a consequence of the scarce anatomical information available for Isomeria and the low number of species used in the cladistic analysis. The identified synapomorphies were: 1) aperture shape quadrangular; 2) presence of palatal teeth in the aperture and 3) umbilicus partially or entirely covered by lip. Characters shared with Labyrinthus are the presence of hooked denticles in the penis, which are smaller in Isomeria ; the penis­epiphallus reflection usually wrapped in part by penis sheath. The free oviduct formed an angle with vagina. The jaw in Isomeria (as it is the case in some species of Labyrinthus ) is smooth with transverse striae, not ribbed.