Discartemon discus (Pfeiffer, 1853) [ "1851" ]

Siriboon, Thanit, Sutcharit, Chirasak, Naggs, Fred, Rowson, Ben & Panha, Somsak, 2014, Revision of the carnivorous snail genus Discartemon Pfeiffer, 1856, with description of twelve new species (Pulmonata, Streptaxidae), ZooKeys 401, pp. 45-107 : 52-54

1. Discartemon discus (Pfeiffer, 1853) [ "1851"] Figs 4 A–C, 11 A–C, 22A, 23, Table 1

Streptaxis discus Pfeiffer, 1851: 252. Type locality: Unknown. Pfeiffer 1853: 289. Pfeiffer 1854: 394, 395, pl. 145, figs 15-17. Ancey 1884: 399. Tryon 1885: 66, pl. 16, figs 77-79. Gude 1903: 226.

Discartemon discus - Bourguignat 1899: 46. Richardson 1988: 182. Schileyko 2000: 784, fig. 1022.

Streptaxis (Discartemon) paradiscus Möllendorff, 1900: 117. Type locality: Phucson bei Touranne, Annam. Gude 1903: 227. Ancey 1904: 289, 290.

Odontartemon (Discartemon) discus - Kobelt 1906: 97, pl. 55, figs 5-7.

Odontartemon (Discartemon) paradiscus - Kobelt 1906: 97, 98, pl. 55, figs 8, 9.

Discartemon paradiscus - Benthem Jutting 1954: 79. Zilch 1960: fig. 1961. Zilch 1961: 82, pl. 5, fig. 3. Schileyko 2011: 22, 23.

Material examined.

This species was described from specimens from the H. Cuming collection. The number of specimens was not indicated, but only one set of measurements was given in the original description. Only one specimen from the H. Cuming collection at NHMUK has Pfeiffer’s handwriting on the species name label. It is identical to the illustration and measurements in Pfeiffer (1854: 394, 395, pl. 145, figs 15-17) and is designated here as the lectotype to stabilize the name: NHMUK 20130684 (Fig. 4A).

Lectotype of Streptaxis paradiscus Möllendorff, 1900 SMF 108534 (Fig. 4B) and paralectotypes SMF 108535 (5 shells). Marble Mountain, Da Nang, Vietnam (16°0'13.4"N, 108°15'49.1"E): CUMZ 6001 (39 shells; Fig. 4C), 6257 (6 specimens in ethanol; Figs 11A, B, 22A). Annam: MNHN Jousseaume Coll. (1 shells), MNHN Denis Coll. (2 shells), MNHN Letellier Coll. (3 shells), NHMW 40858 (2 shells), NHMUK 1901.12.23.13-14 (2 shells), NHMUK Trechmann coll. Acc. 2176 (2 shells), NHMUK Connolly Coll. Acc. 2154 (1 shell), RMNH Fruhstorfer Coll. 45a (1 shell), RMNH Saverbgen Coll. (2 shells). Tourane [=Da Nang], Central Annam: NHMUK McAndrew coll. Acc. 1563 (2 shells). Touraine, Annam: NHMW Rusnov Coll. R 283 (2 shells), NMW 1955.158.25251 (1 shell), RMNH Verdcourt Coll. (2 shells), ZMB 6619 (3 shells), ZMB 52300 (3 shells). Phuc-Son, Annam: NHMW 31140 (1 shell).

Description.

Shell. Shell flattened, white and translucent; whorls 6 –6½; spire flattened with distinct suture. Shell surface glossy, smooth with growth lines and varices present. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl angular, regularly expanded; umbilicus very wide, shallow and showing all preceding whorls. Aperture semi-ovate; peristome discontinuous, thickened, expanded and reflected; apertural dentition with only one parietal lamella (Fig. 4 A–C).

Radula. Each row consists of 61-67 teeth with formula (30-33)-1-(30-33). Central tooth very small and triangular with pointed cusp. Lateral and marginal teeth undifferentiated, unicuspid and lanceolate. Latero-marginal teeth gradually reduce in size, with outermost teeth smaller and shorter than inner teeth (Fig. 22A).

Genital organs. Atrium (at) short; penis (p) long and slender. Penial sheath (ps) thin, extending about half to third-fourths of penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserting at distal end of penial sheath (Fig. 11A). Vas deferens (vd) passes through a very short part of penial sheath before entering into penis distally (Fig. 11B). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.

Vagina (v) long, cylindrical, about two thirds of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) short; oviduct (ov) enlarged and folded. Prostate gland inconspicuous and bound to oviduct. Talon (ta) small. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 11A).

Pallial system. Excretory system typically sigmurethran and without mantle gland. Heart (h, auricles and ventricle) located left of kidney (on right in Fig. 11C). Pulmonary cavity approximately three times longer than broad. Pulmonary vein (puv) and venation on lung roof distinct and well developed. Kidney (k) very short, located at posterior of pulmonary cavity. Ureter (ur) sigmoid, closed tube arising from apex of kidney, extending along right side of kidney, recurving adjacent to rectum (rt). Anus (a) adjacent to pneumostome (pn) on mantle collar.

Remarks.

The type specimen discovered in the H. Cuming collection at NHMUK elucidates two issues. Firstly, Streptaxis paradiscus Möllendorff, 1900 has been recognized as a separate species in many works ( Möllendorff 1900, Gude 1903, Kobelt 1906, Benthem Jutting 1954, Zilch 1960, 1961, Schileyko 2011). However, based on the type specimens, Discartemon discus and Streptaxis paradiscus are identical in all shell characters. Therefore, we officially place Streptaxis paradiscus as a junior subjective synonym of Discartemon discus . Second, Discartemon discus had an unknown type locality and range ( Pfeiffer 1851: 252). From the new material and the type locality of Streptaxis paradiscus , the distribution of this species is demarcated to several localities in the area of Da Nang, Vietnam ( Schileyko 2011).

The record of Streptaxis discus from Brazil, mentioned in Bourguignat (1899) is almost certainly an error, since it is far beyond the distribution range of the genus. The specimen figured in Simone (2006: 191, fig. 708, reg. NHMUK Trechmann Acc. 2176) has the locality Annam [= central Vietnam].