Indoartemon medius Siriboon & Panha, 2014

Siriboon, Thanit, Sutcharit, Chirasak, Naggs, Fred, Rowson, Ben & Panha, Somsak, 2014, Revision of the carnivorous snail genus Indoartemon Forcart, 1946 and a new genus Carinartemis from Thailand (Pulmonata: Streptaxidae), Raffles Bulletin of Zoology 62, pp. 161-174 : 164-166

Indoartemon medius Siriboon & Panha , new species

( Figs 1 , 2A , 3 E–G, 4A–C, 5A–I, Table 1)

Material examined. Holotype CUMZ 5016 ( Fig. 3E ). Measurement: height 8.8 mm, width 9.2 mm, 7 whorls . Paratypes: CUMZ 5017 (56 shells; Fig. 3F ) , CUMZ 6206 (28 specimens in ethanol) , NHMUK 20130076 (2 shells) , SMF (2 shells), and ZRC (2 shells).

Type locality. Wat Chuak Charoentham, Ban Rai , Uthai Thani, an isolated limestone hill about 200 m above mean sea level (15°16'26.3"N, 99°41'43.4"E) .

Other material examined. Tam Lom-Tam Wang, Si Samrong, Sukhothai. Shells slightly smaller than specimens collected from Uthai Thani ( CUMZ 5018 , Fig. 3G ) .

Etymology. The specific epithet “ medius ” is derived from the Latin “ medius ” meaning “middle”. It refers to the distribution range of this new species in central Thailand.

indicated in parentheses.

Diagnosis. Indoartemon medius , new species, can be distinguished from I. cingalensis and I. fuchsianus ( Gredler, 1881) in its higher spire, the last whorl being less deviated from the vertical axis, the left periphery of the penultimate whorl being keeled, and the absence of a columellar lamella. Indoartemon laevis differs from I. medius , new species, in its lower spire, the left periphery of the penultimate whorl being rounded and not extending beyond the diameter of the last whorl, and the presence of a basal lamella. Indoartemon prestoni possesses a distinct suture, the left periphery of the penultimate whorl extends beyond the diameter of the last whorl, and the umbilicus is wider. Indoartemon medius , new species, can be distinguished from the type species by its larger shell, the left periphery of the penultimate whorl being shouldered, last whorl being more deviated from the vertical axis, its wider umbilicus, and semi-ovate aperture.

Description. Shell oblique-heliciform, white, and translucent; whorls 7, spire conical with indistinct suture. Shell surface glossy, with fine transverse ridges that diminish below the periphery. Embryonic shell with about 2½ whorls and smooth surface; following whorls regularly expanded. Shell periphery keeled; last whorl axially deflected. Umbilicus narrow and deep. Aperture subcircular; peristome discontinuous, thickened and slightly expanded. Apertural dentition with one parietal lamella and one palatal lamella ( Fig. 3E ).

Radula. Teeth arranged in anteriorly V-shaped rows, each row containing 33–37 teeth with the formula (16-18)-1- (16-18); central tooth small, short, triangular with pointed cusp. Lateral and marginal teeth undifferentiated, unicuspid and lanceolate; lateral teeth gradually reduced in length and size with outer teeth much smaller and shorter than inner teeth ( Fig. 5I ).

Genital organs. Atrium (at) short. Proximal penis (p) long slender; becoming slightly broader before tapering distally. Penial sheath (ps) thin, extending about half of total penis length, penial sheath retractor muscle (psr) very thin, originating at atrium, inserting distally on penial sheath ( Fig. 4A ). Vas deferens (vd) slender, attached to distal end of penial sheath by a narrow band of connective tissue ( Fig. 4B ). Penial retractor muscle (pr) thin and very long, inserting distally on penis at the penis and vas deferens junction.

Internal wall of atrium possesses numerous atrial pores ( Fig. 5A ). Proximal penial wall with scattered and pale brown penial hooks about 3 hooks/200 μm 2; hooks withdrawn into penial papillae separated by low reticulated folds. Proximal penial hooks are minute (<0.01 mm in length), tips obtuse and curved towards genital orifice ( Fig. 5C, D ). Distal penial wall with pale brown penial hooks about 5 hooks/200 μm 2; hooks located on penial papillae (pl). Penial papillae may extend across penial hook and adjacent areas with low reticulated folds ( Fig. 5E, F ). Distal minute penial hooks with obtuse tips (<0.01 mm in length) expanded at base and curved towards genital orifice ( Fig. 5G ).

Vagina (v) short, stout, about quarter of total penis length. Gametolytic duct (gd) long, extending as far as albumin gland; gametolytic sac ovate (gs). Free oviduct (fo) stout and long. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct ( Fig. 4A ). Talon (ta) small, very short, and club shaped ( Fig. 4C ). 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. Vaginal wall with oblique parallel vaginal folds; vaginal hooks absent ( Fig. 5H ).

Animal. Live specimens exhibit yellowish to orange reticulated skin, and orange tentacular retractor muscles are visible through the semi-transparent body ( Fig. 2A ).

Figures

Fig. 1. Distribution map of Indoartemon spp. and Carinartemis spp. Indoartemon spp (white circle): (1) Indoartemon cingalensis (Benson, 1853); (2) Indoartemon layardianus (Benson, 1853); (3) Indoartemon glacilis (Collett, 1898); (4) Indoartemon eburneus (Pfeiffer, 1861); (5) Indoartemon fuchsianus (Gredler, 1881); (6) Indoartemon bidens (Möllendorff, 1883); (7) Indoartemon tridens (Möllendorff, 1898); (8) Indoartemon laevis (Blanford, 1899); (9) Indoartemon prestoni (Gude, 1903); and (10) Indoartemon medius, new species. Carinartemis spp. (black circle): (1) Carinartemis vesperus, new species; and (2) Carinartemis striatus, new species.

Fig. 2. Living snails of: A, Indoartemon medius, new species, paratype CUMZ 5017 (shell width about 8 mm); B, Carinartemis vesperus, new species, paratype CUMZ 6201 (shell width about 10 mm); C, Carinartemis striatus, new species, paratype CUMZ 6205 (shell width about 12 mm).

Fig. 3. Shells of Indoartemon spp: A, B, Indoartemon eburneus, (A) lectoype NHMUK 20120255, and (B) specimen CUMZ 5014, with apertural dentition, from Wat Tam Phalom, Loei; C, D, Indoartemon prestoni, (C) lectotype NHMUK 1922.8.29.5, and (D) specimen CUMZ 5015, with apertural dentition, from Wat Tam Ra-Khang, Si Samrong, Sukhothai. E–G, Indoartemon medius, new species, (E) holotype CUMZ 5016 with apertural dentition, (F) paratype CUMZ 5017, and (G) specimen CUMZ 5018 from Tam Lom-Tam Wang, Si Samrong, Sukhothai.

Fig. 5. Internal sculpture of genitalia of Indoartemon medius, new species, paratype CUMZ 5017: A, details of atrial pore on the atrium surface; B, low magnification shows arrangement of penial hooks; C, high magnification of penial hooks in proximal area; D, top view of penial hook, hooks shrunken in tubed penial papillae; E, low magnification of penial hook in distal area; F, lateral view of penial hook in distal area; G, high magnification of penial hooks in distal area; H, arrangement of vaginal folds; I, radula morphology.

Fig. 4. Genitalia of Indoartemon medius, new species, paratype CUMZ 5017: A, reproductive system; B, attachment of vas deferens into distal end of the penial sheath; C, details of albumin gland and talon.