Nitor Gude, 1911

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 : 58-59

Nitor Gude, 1911

Thalassia Albers & Martens, 1860: 59 . Type species Helix subrugata Reeve, 1852 (OD) [not Gistel, 1848].

Nitor Gude, 1911: 270 [nom. nov. for Thalassia Albers & Martens, 1860 non Gistel, 1848].

Modonitor Iredale, 1937c: 3 . Type species Helix pudibunda Cox, 1868 (M).

Melocystis Iredale, 1937c: 5 . Type species Helix circumcincta Cox, 1868 (OD).

Description. External morphology: Shell 4.3–6.2 whorls, glossy, spire and apex slightly raised. Protoconch sculptured with incised spiral grooves; teleoconch with microscopic spiral grooves. Whorl profile flattened above and rounded ( Nitor subrugata ) or flattened ( N. circumcincta , N. wiangariensis ) below a rounded to angulate periphery. Internal walls of early whorls complete; umbilicus closed ( N. wiangariensis ) or narrowly open ( N. circumcincta , N. subrugata ). Right mantle lap short to very short, left mantle lap short to absent, both mantle laps narrow, finger-shaped, not fused, uniform in colour. Right and median mantle lobes of moderate size, thick, left mantle lobe very small. Caudal apparatus as for genus; caudal foss vertical or diamond-shaped slit in tail.

Mantle cavity: Mantle with visible minor blood vessels; pigmentation absent ( N. subrugata ), of white spots ( N. wiangariensis ), or of black and white spots ( N. circumcincta ).

Digestive system: Oesophageal crop absent.

Genital system: Carrefour embedded in albumen gland, talon free (only observed in N. circumcincta ). Free oviduct of medium length; capsular gland present; internal longitudinal pilasters present. Bursa copulatrix inserted on vagina, short, less than half spermoviduct length; duct of bursa copulatrix wide, not distinguishable from bursa copulatrix, internally smooth ( N. wiangariensis , N. subrugata ) or with longitudinal pilasters ( N. circumcincta ). Vagina internally with longitudinal pilasters. Epiphallus enters penis through two fleshy lips ( N. circumcincta ) or a short verge ( N. wiangariensis , N. subrugata ); penis internally flat, longitudinal penis pilasters present, diverticulum on penis absent. Penial sheath present, enclosing only penis ( N. subrugata , N. wiangariensis ) or enclosing only base of penis ( N. circumcincta ); penis retractor muscle attached to tip of epiphallic caecum. Epiphallus internally with longitudinal pilasters. 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 narrow teeth.

Radula (only examined in N. circumcincta ): Relatively long and narrow. Central tooth with small ectocones; mesocone lanceolate, shorter than tooth base. Lateral and marginal tooth fields distinguishable. Lateral teeth with endocone smaller than central tooth ectocones; ectocone equal in size to those on central tooth; mesocone shorter than tooth base. Marginal teeth with endocones absent; ectocones not subdivided into extra teeth.

Remarks. A detailed description of the nomenclatural history of Nitor was given by Hyman (2007) and is not repeated here. The description of Nitor given below is based on three species: Nitor subrugata , Nitor circumcincta and Nitor wiangariensis Hyman, 2007 . Nitor wiangariensis was described in full by Hyman (2007) and a description is therefore omitted from the current study.

Nitor is here grouped with a number of other genera of snails with a smooth, slender flagellum ( Expocystis , Malandena , Pravonitor and Westracystis ). However, there are considerable anatomical differences separating these genera. Malandena and Expocystis possess no distinct vagina; Pravonitor and Westracystis have a short vagina; while the three Nitor species have a distinct, moderately long vagina. In addition, in all Nitor species the penis retractor muscle attaches to the tip of a moderately long epiphallic caecum, while it attaches to the base of the caecum in Expocystis and Westracystis , the middle of the caecum in Pravonitor , and to the epiphallis in Malandena . Also, in Nitor and Westracystis , the interior of the penis has multiple distinct longitudinal pilasters, whereas in the other genera irregular longitudinal pilasters or ridges ( Malandena , Expocystis ) or pustules ( Pravonitor ) are present. Finally, the spermatophore was observed in E. rustica and in all three Nitor species. It was similar in general shape, but differed in the shape of the teeth present on the tail-pipe. In Nitor the teeth were small and very narrow, more similar to short spines than teeth, whereas in Expocystis small triangular teeth were present.