Tarocystis 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 : 78

Tarocystis Iredale, 1937

Tarocystis Iredale, 1937c: 4 . Type species Microcystis responsivus Hedley, 1912 (OD).

Description. External morphology: Shell 4 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 Ushape. Mantle laps moderately small, narrow, not fused, uniform in colour. Right and median mantle lobes small, left mantle lobe very small. 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. Talon and carrefour not examined. Free oviduct of medium length; capsular gland absent; internal longitudinal pilasters absent. Bursa copulatrix inserted on vagina, short, less than half spermoviduct length; duct of bursa copulatrix wide, not distinguishable from bursa copulatrix, internally smooth. Vagina moderately long, internal structure not examined. Epiphallus enters penis through simple pore; penis internally flat, longitudinal penis pilasters present, penial diverticulum absent. Penial sheath present, enclosing only penis; penis retractor muscle attached to epiphallus. Epiphallus internally with longitudinal pilasters. Epiphallic retractor caecum absent. Flagellum and lime-sac absent. Spermatophore not present in dissected material.

Radula: Relatively long and narrow. Central tooth with small ectocones; mesocone lanceolate, longer than tooth base. Lateral and marginal tooth fields distinguishable. Lateral teeth with endocone much smaller than central tooth ectocones; ectocone equal in size to those on central tooth; mesocone longer than tooth base. Marginal teeth with endocones absent; ectocones approximately same length and breadth as mesocone, not subdivided into extra teeth.

Remarks. Tarocystis was described by Iredale (1937c) for Microcystis responsivus Hedley, 1912 , M. fulva Odhner, 1917 and M. antiqua Odhner, 1917 , all from northern Queensland. Odhner (1917) described and figured the genitalia, radula and jaw of T. fulva and the radula and jaw of T. responsivus . Smith (1992) and Smith et al. (2002) listed all three species under Tarocystis .

Tarocystis responsivus lacks an epiphallic flagellum or caecum, but is placed in Helicarionidae primarily on the shell sculpture. The absence of spiral and radial ribs on the teleoconch and the presence of spiral grooves on the protoconch and teleoconch indicates affinity with Helicarionidae rather than Euconulidae , although the phylogenetic analysis shows that it is the most basal helicarionid.