Labyrinthus subplanatus (Petit, 1843)

Figures 13–22

Caracolla subplanatus Petit, 1843, 238.

Description: Shell: Morphology as described by Solem (1966: 116), (Fig. 13).

Pallial Organs: Kidney long, thin, occupying about 60% of pulmonary roof length. Surface of pulmonary roof densely speckled with dark spots. Thin transversal veins abundant between kidney and rectum. Main pulmonary vein branched before reaching mantle collar. Pulmonary roof not expanded beyond top of kidney. Secondary ureter closed up to mantle collar. Ureteric interramus triangular, deeply excavated. Diaphragm thick, muscular.

Reproductive system (Figs 14–16): Ovotestis formed by elongated digitiform nonramified acini. Albumen gland yellowish, bean­shaped. FPSC undifferentiated. Hermaphroditic duct reflexed over itself at base of albumen gland. Albumen gland continuous with spermoviduct. Folds of uterine portion transversal with respect to longitudinal axis of spermoviduct (Fig. 14). Free oviduct short, cylindrical, naturally forming angle with vagina. Prostatic duct of spermoviduct extending into proximal portion of free oviduct. Vagina as long as penis. Proximal portion of vagina with inner thick longitudinal ridges in zigzag pattern. Distally, ridges become thinner, straight. Hooked denticles absent in entire length of vagina. Duct of bursa copulatrix long, thick, parallel to spermoviduct up to junction with albumen gland. Bursa copulatrix sac globose, reflexed over duct (Fig. 14). Penial complex formed by flagellum, epiphallus, penis (Fig. 15). Diameter of flagellum progressively decreasing towards tip. Thick internal pilaster extending between flagellum and epiphallus. Pilaster forming papilla­like structure transversally divided at junction between flagellum and epiphallus, point of insertion of vas deferens (Fig. 16). Penis sheath thick, muscular overlapping distal zone of penis. Epiphallus reflexed over penis, wrapped with muscular fibres and connective tissue. Distal zone of penis thicker than proximal. Penis retractor muscle thick, inserting at proximal portion of penis close to junction with epiphallus. Inner penis wall with thick folds, deeper in proximal zone. Dorsal surface of folds with white, oval, hooked pustules, regularly distributed as shown in Fig.16. Verge absent.

Digestive system: Jaw (Figs 17–18) arched, without vertical ribs (Fig. 17). Surface with thin transverse striation crossed by thin, shallow perpendicular lines giving appearance of reticulated surface (Fig. 18). Lower edge without medial protruded cutting edge.

Central tooth of radula unicuspid, triangular (Fig. 19). Fourteen lateral teeth unicuspid (Figs 19, 20). Marginal teeth tricuspid (Fig. 21). Outermost marginal teeth becoming wider but always tricuspid with more pronounced mesocones (Fig. 22). Buccal mass oval. Rest of digestive tract as in L. dunkeri .

Material examined: COLOMBIA: FMNH 163706, Choco Department, Choco, Caño Taparral, 20 Km to the north of Palestina, on San Juan River. November 25, 1968. B. Malkin Coll. FMNH 173866, Choco Department, San Juan River, Quebrada Docordo. June 5–8, 1969. B. Malkin Coll. FMNH 223561, Choco Department, San Juan River, 110 Km to the north of Palestine. January 20,1971. B. Malkin & P. Bouchard Coll.

Remarks: Labyrinthus subplanatus belongs to the L. otis species complex that was supported as a monophyletic clade within the genus (Cuezzo 2003). The group of L. otis is composed by L. otis (Lightfoot, 1786), L. subplanatus, L. marmatensis Pilsbry, 1910, and L. plicatus . Labyrinthus subplanatus is similar to L. otis and both have been confused mostly because their distributional ranges are partly overlapping. However, L. otis differs from L. subplanatus mainly in having a deep supraperipheral groove and in being much larger ( L. otis shell diameter up to 58 mm, while L. subplanatus diameter up to 45 mm). Labyrinthus subplanatus also present a periphery acutely angulated with protruding keel, and the peristome forming a peripheral notch sometimes slightly twisted (see Solem 1966) which is absent in L. otis . Differences in the genitalia between these two species are difficult to evaluate because of the poor descriptions presently available of L. otis .