Expocystis Iredale, 1937

Hyman, Isabel T. & Ponder, Winston F., 2010, A morphological phylogenetic analysis and generic revision of Australian Helicarionidae (Gastropoda: Pulmonata: Stylommatophora), and an assessment of the relationships of the family 2462, Zootaxa 2462 (1), pp. 1-148 : 65

Expocystis Iredale, 1937

Expocystis Iredale, 1937c: 4 . Type species Helix rustica Pfeiffer, 1852 (OD).

Description. External morphology: Shell of about 5 whorls, glossy, spire and apex slightly raised. Protoconch sculptured with incised spiral grooves; teleoconch with microscopic spiral grooves. Whorl profile rounded above and below evenly convex periphery. Internal walls of early whorls complete; umbilicus open, very narrow U-shape. Mantle laps short, narrow, finger-shaped, not fused, uniform in colour. Right and median mantle lobes small, left mantle lobe absent. Sole of foot and caudal apparatus as for family.

Mantle cavity: As for family; mantle with no visible minor blood vessels, pigmentation absent.

Digestive system: Oesophageal crop absent.

Genital system: As for family. Carrefour and talon both not embedded in albumen gland. Free oviduct of medium length; capsular gland present; internal longitudinal pilasters absent. Bursa copulatrix inserted at junction of penis and free oviduct, moderately long, more than half spermoviduct length; duct of bursa copulatrix narrow, distinguishable from bursa copulatrix, internally with transversely elongate pustules. Vagina absent. Epiphallus enters penis through simple pore; penis internally covered in irregular ridges, longitudinal penis pilasters present, penial diverticulum absent. Penial sheath present, enclosing only penis; penis retractor muscle attached to base of epiphallic caecum. Epiphallic retractor caecum moderate in size, positioned in middle of epiphallus. Flagellum present; flagellum and distal part of epiphallus without internal cryptae and externally smooth and slender. Spermatophore soft capsule with firm tail pipe open at one end; tail pipe long, sculptured with longitudinal rows of tiny teeth.

Radula: Relatively long and narrow. Central tooth with small ectocones; mesocone lanceolate, shorter than tooth base. Lateral and marginal tooth fields distinguishable. Lateral teeth with small endocone; ectocone equal in size to those on central tooth; mesocone shorter than tooth base. Marginal teeth with endocone absent; ectocone shorter and narrower than mesocone, subdivided into extra teeth at outer edge of radula only.

Remarks. This genus was introduced by Iredale (1937c) for Helix rustica Pfeiffer, 1852 from southern Queensland on the basis of radular differences shown by Odhner (1917). Iredale later added another species, ‘Expocystis’ exclusus ( Iredale 1941) . This species was moved to Melocystis by Smith (1992), who recognised only a single species in Expocystis , E. rustica .

Illustrations of the shell of Expocystis rustica were provided by Cox (1868) and Tryon (1886) and the penial complex and radula by Odhner (1917).

Expocystis can be differentiated from Nitor by its rounded whorl profile, the lack of a distinct vagina and the attachment of the penis retractor muscle to the base of the caecum rather than the tip. The genus can be distinguished from Pravonitor by its smaller size, by the attachment of the penis retractor muscle to the base of the caecum and by its straight and uncoiled flagellum. Westracystis differs from Expocystis in the presence of a vagina, and Malandena differs in the absence of an epiphallic caecum.