Dyakia janus ( Beck, 1837 )

Sutcharit, Chirasak, Tongkerd, Piyoros, Tan, Shau-Hwai Aileen & Panha, Somsak, 2012, Taxonomic Revision Of Dyakia Janus From Peninsular Malaysia (Pulmonata: Dyakiidae), With Notes On Other Sinistrally Coiled Helicarionoids, Raffles Bulletin of Zoology 60 (2), pp. 279-287 : 280-285

Dyakia janus ( Beck, 1837)

Figs. 1B–F , 3 ; Table 1

Helix Ianus bifrons Chemnitz, 1795: 307, 308, pl. 213, Figs. 3016, 3017, type locality: Südsee [Rejected species-group name by the commission (ICZN, 1944: Opinion 184)]

Nanina (Ariophanta) janus Beck, 1837: 5 , type locality: Südsee (= Islands of South Sea ) and Java

Helix janus: Pfeiffer, 1847: 88 , 89, pl. 11, Figs. 4–6; Pfeiffer, 1848: 77

Helix sannio Pfeiffer, 1854: 57 , type locality: unknown; Pfeiffer, 1859: 253

Nanina albersi Martens, 1864: 265 , type locality: Malakka; Martens, 1867: 224, 225, pl. 2, Fig. 3 ; Tryon, 1886: 20, pl. 3, Fig. 37

Nanina sannio: Tryon, 1886: 18 , pl. 2, Fig. 26

Nanina janus: Tryon, 1886: 19 , pl. 3, Figs. 34, 36

Dyakia albersi: Gude, 1903: 49

Dyakia sannio: Laidlaw, 1931: 191 , 201; Laidlaw, 1933: 234; Laidlaw, 1963: 146; Maassen, 2001: 107

Dyakia janus: Laidlaw, 1931: 192 , 200; Laidlaw, 1933: 226; Laidlaw, 1963: 141, 142; Maassen, 2001: 105

Type material. — Designated neotype BMNH 42.5 .10.1463 ( Fig. 1B , height 23.9 mm, width 37.5 mm, 6¾ whorls). Based on the neotype, the type locality is Mount Ophir, peninsulae Malaccanae [=Gunung Ledang, Johor, Malaysia (02°22'N, 102°36'E)].Additional material from the same lot of neotype BMNH 42.5.10.1464–5 (2 shells, height 23.5, 24.2 mm, width 35.5, 36.1 mm, 6¾ whorls) .

Other material. — The specimen that most closely matches the description and measurements given in the original description is designated here as the lectotype of Helix sannio Pfeiffer, 1854 , BMNH 20100242.1 ( Fig. 1E ), and paralectotype BMNH 20100242.2 (1 shell) . Syntypes of Nanina albersi Martens, 1864 , ZMB 57526 ( Fig. 1F ) and 57525 are from Malacca . Other specimens from Malacca, Malaysia: BMNH 1904.5 .26.36 (1 shell), 58.5.12.267 (3 shells), A. S. Kennard coll. (1 shell). Perak, Malay Peninsular: BMNH 97.3.13.5–6 (2 shells), 92.8.24.24 (1 shell). Batang Padang , Malay Peninsula : BMNH 97.3.15.17–18 (2 shells). Gunung Benom , Malaya : BMNH ex. University of Malaya coll. (1 shell). Bukit Besar , Malaysia: BMNH 1904.5 .26.36 (1 shell). Pulau Besar , Mersing , Johor, Malaysia (2°26'17.24"N, 103°58'51.75"E): CUMZ 4918 , 4919 ( Fig. 1C ). Südsee [=Islands of South Sea] ex. Spengler collection ZMUC GAS- 411 ex. Spengler’s coll. dated before 1795 (2 shells, fragile juveniles) .

Taxonomic remarks. — Chemnitz (1795) species level names, including Helix Ianus bifrons, were rejected by the ICZN (1944) on the basis that binomial nomenclature was not consistently maintained in this work. The combination Nanina (Ariophanta) janus was made available by Beck (1837) and specimens in “Mufeo Spengleriano” as indicated by Chemnitz (1795: 309), and known to H. Beck (1837), are acknowledged as the original type series ( ICZN, 1999: Art. 72.4). Unfortunately, both syntype lots cannot be located and are assumed to be lost. The nominal species-name is considered as doubtful application and confusing status. In addition, Chemnitz’s figures are poor and inadequate for recognising the identity of this species ( Fig. 1D ). We therefore consider Nanina (Ariophanta) janus Beck, 1837 to be a nomen dubium. However, the species has been consistently known and understood sensu Pfeiffer (1847; Fig. 1B ). Pfeiffer provided an accurate figure and description for the specimen, on which he based his descriptions ( Pfeiffer, 1842: 87; 1847: 88, 89). Therefore, this specimen is designated herein as the neotype ( BMNH 42.5.10.1463, Fig. 1B ).

Shell. — Shell large, depressed conic, thickened and sinistral. Whorls 6–7, increasing regularly, slightly convex, with very wide and shallow suture. Spire convex; apex acute; embryonic shell smooth; following whorls with thin growth lines and spirally undulated surfaces. Last whorl rounded to shouldered, with slight peripheral keel that disappears proximal to the aperture; a narrow dark brown peripheral band usually present; periostracum thin corneous. Upper shell surface shades of pale to somewhat darker brown; lower shell surface usually darker brown. Aperture ovate; lip slightly thickened in adult snails. Columella slightly dilated; parietal callus thin and translucent. Umbilicus narrow and deep.

Genitalia. — Atrium (at) very short. Penis (p) proximally enlarged, cylindrical, and tapering to small tube. Penial retractor muscle (rm) thin and long. Epiphallus (e) long and slender tube, similar in length to penis and with similar diameter to distal part of penis; flagellum absent. Vas deferens (vd) relatively small and thin tube extending from free oviduct (fo) and entering the epiphallus distally. Internal wall of penis: proximally with large and irregular penial pilasters (pp) for around one-third length of chamber; distally with very thin, smooth longitudinal pilasters; penial verge absent ( Fig. 3A, B ).

Gametolytic duct (gd) a long and large cylinder, distally with elongated and bulbous gametolytic sac (gs). Amatorial organ (am) well developed, large elongated cylinder; proximally attached to gametolytic duct. Amatorial organ gland (amg) composed distally of three major lobes bounded to amatorial organ by thin connective tissue. Each of the three major lobes of the amatorial organ gland extends proximally into thin ducts (ad) that are twisted together and bound with thin connective tissue before fusing prior to entering the distal tip of the amatorial organ. The internal wall sculpture of the amatorial organ consists of small longitudinal amatorial organ pilasters (amp); proximally these are interrupted to produce irregular papillary knobs arranged in lines that occupy onethird of the chamber; distally they are connected to form uninterrupted longitudinal pilasters. The conical amatorial organ papilla (ap) is tipped by a small calcified spike ( Fig. 3A, B ).

Vagina (v) long, cylindrical, and surrounded by sponge-like tissue. Internal wall of introverted chamber consists of strong irregular shaped but smooth pilasters (vp). Oviduct (ov) long, with lobules; prostate gland bound to oviduct.Albumen gland (ag) large and lingulate. A small convoluted hermaphrodite duct (hd) connects lobules of the hermaphroditic glands (hg) with the talon ( Fig. 3A, B ).

External features. — Living snail with long and greyishbrown tentacles. Skin reticulated brown with black reticulations around head. Foot sole relatively elongated, broad and unipartite. Sole of foot brownish and unspotted; side of body brownish; upper part of tail appears dark greyish. Tail long, curved mid-dorsally, tall dome-shaped in cross section. Caudal horn not overhanging; caudal foss, short vertical slit in tail above sole margin. Pedal groove typical aulacopodoid and well defined ( Fig. 3C ).

Viewed internally (thus with reversed left/right orientation in Fig. 3D ), mantle collar with large shell lobes. Left dorsal lobe (ldl) large and thickened. Right dorsal lobe (rdl) undivided. Small ear-shaped posterior right dorsal lobe (prdl) present. Right and left shell laps absent ( Fig. 3D ).

Pulmonary cavity with typical sigmurethan heart (h, auricle and ventricle) located near the kidney (k). Pulmonary cavity approximately four times longer than broad. Pulmonary vein (pv) and venation on lung cavity well developed and distinct. Kidney (k) elongated and slender, approximately one-third of pulmonary cavity length. Ureter (ur) sigmoid, closed tube arising from tip of kidney, extending along the kidney, and curved adjacent to rectum (r). Anus (an) adjacent to mantle collar ( Fig. 3D ).

Radula. — Teeth arranged in V-shaped rows with approximately 134 (68-(15-20)-1-(15-20)-65) teeth. Central tooth symmetric unicuspid and sword-shaped. Lateral teeth asymmetric unicuspid, sword-shaped, and inclined towards central tooth. Marginal teeth start from tooth 15–20, elongate sword-shaped, apically pointed; outermost teeth shorter and apically more rounded than inner teeth ( Fig. 3E ). Jaw smooth (without vertical ribs), crescentic, with anteriorly convex cutting margin.

Distribution. — Chemnitz (1795) gave the locality of this species as “Islands of the South Sea” ( Laidlaw, 1931: 193), and “Java” was subsequently (and inaccurately) added by Beck (1837). The type locality is Mount Ophir, peninsular Malaccanae. Further distribution records demonstrated its geographic range to be restricted to the southern region of peninsular Malaysia: Mount Ophir, Malacca ( Pfeiffer, 1847); Malaya, Billiton, Bangka, Selangor, Malacca, Pulau Aor in Johor, Sungei Rumpon in Pahang, and Singapore ( Laidlaw, 1931, 1933, 1963; Benthem Jutting, 1949). Fresh material examined in the current study is from Pulau Besar, a small granitic island about 10 km from Mersing, Johor, off the east coast of peninsular Malaysia.

Figures

Fig. 1. Shells of Dyakia species. A. Syntype of Dyakia hugonis (BMNH 1975118). B–F. Dyakia janus; B, neotype (BMNH 42.5.10.1463) from Malacca, Malaysia; C, examined specimen from Johor, Malaysia (CUMZ 4919); D, figures of “Helix janus bifron” after Chemnitz (1795, pl. 213, Figs. 3016, 3017); E, lectotype of Helix sannio Pfeiffer, 1854 (BMNH 20100242); and F, syntype of Nanina albersi Albers, 1864 (ZMB 57526). G. Syntype of Dyakia kintana (MNHN, 8 shells). H. Holotype of Dyakia lindstedti (BMNH).

Fig. 3. Genitalia, pallial system, caudal region, and radula morphology of Dyakia janus from Johor, Malaysia (CUMZ 4919). A. Whole genital organ. B. Internal wall sculpture of penis, amatorial organ and vagina. C. Left view of caudal region. D. Pallial system, lung cavity and ventral view of mantle edge. E. SEM image of radula; central tooth indicated by ‘C’. Numbers indicate tooth order from lateral to marginal end.