Atopos transversus, Mitchueachart & & Panha & Somsak, 2025

Atopos transversus , new species

( Figs. 3, 4C, D, 5D)

Type materials. Holotype: One ethanol-preserved specimen ( Fig. 3A, B; length 33 mm, width and height 5 mm) ( CUMZ 160202 View Materials ), in a forest among the limestone hills at Montawa Cave, Taunggyi District, Shan State, Myanmar, 20°45′16.8″N 97°01′03.4″E GoogleMaps . Paratypes: One ethanol-preserved specimen ( Fig. 3C; length 27 mm, width 6 mm, height 5 mm) ( CUMZ 160203 View Materials ), same locality as the holotype. One ethanol-preserved specimen ( Fig. 3D; length 45 mm, width 8 mm, height 9 mm) ( CUMZ 160204 View Materials ), Myin Ma Hti Cave (Pagoda), Kalaw Township, Taunggyi District, Shan State, Myanmar, 20°35′56.3″N 96°36′36.9″E GoogleMaps .

Etymology. The specific name ‘ transversus ’ is from the Latin words ‘trans’ meaning across or cross, and ‘versus’ means stripe or line; these refer to the presence of the crossed stripes on its dorsal side.

Diagnosis. Notum yellowish-brown to pale brown with blackish to brownish cross-reticulated stripes without a distinct pattern. Mid-dorsal keel fairly prominent. Light brown mid-dorsal line with scattered tiny blackish spots. Perinotum and foot pale yellow to off-white. Anterior end with small whitish patch.

External characters. Preserved specimen ( Fig. 3). Animal narrowly elongated cylindrical and tapering to both ends. Dorsal side with fairly prominent mid-dorsal keel along its entire length. Notum rather smooth, and surface with a uniformly low cluster of small- to medium-sized and randomly scattered papillae. Papillae generally rounded, roughened surfaces and with an area of depressions at the centre ( Fig. 4C, D). Anterior end of notum with a small whitish patch. Notum yellowish-brown to pale brown with scattered tiny blackish spots; mid-dorsal line a lighter colour than notum; mid-lateral line absent. Lateral surface of body with irregular and scattered blackish to brownish streaks; sometimes with cross-reticulated stripes. Perinotum narrow with off-white to pale yellow sharp keel; foot narrow, about 2.5-fold narrower than body width ( Fig. 3). Anterior notum covers head region. Head and tentacles off-white; upper tentacle slightly short; lower tentacles short, stout, and bifid.

Genital organs. Male genital pore located at base of lower right tentacle. Atrium long; penis (p) long cylindrical shape and situated at base of right body cavity. Vas deferens (vd) a thin tube, emerging from body wall near the male genital pore before inserting near distal end of penis. Penial retractor muscles (pr) inserted at distal end of penis. Simroth glands present on both sides; left Simroth gland (lsg) much smaller and less developed. Right Simroth gland (rsg) well-developed and consists of three parts: (i) evaginable part (es) is cylindrical shaped and slightly shorter than penis length; (ii) interconnected duct a short, thin, and curled tube; and (iii) secretory part (sp) is cylindrical shaped, curled, long, and slightly larger in diameter than interconnected duct. Simroth gland retractor muscle (sr) attached near distal end of evaginable part ( Fig. 5D).

Female genital pore (fg), anal pore (an), and pulmonary orifice (po) located about 4 to 6 mm from male genital pore in right pedal groove ( Fig. 3A, C, D). Vagina short tubular duct; receptaculum seminis club-shaped; oviduct a coiled and cylindrical tube. Albumen gland (ag), hermaphrodite gland (hg), and prostate gland (pg) bound together and undifferentiable.

Distribution. Atopos transversus , new species, is currently known only from the type locality in Shan State, Myanmar ( Fig. 1).

Comparative diagnosis. This new species can be distinguished from A. laidlawi and Atopos punctata Collinge, 1902 from Thailand, and A. gravelyi by having a fairly prominent mid-dorsal keel, light brown mid-dorsal line, yellowish-brown to pale brown notum with blackish to brownish cross-reticulated stripes in a random arrangement, and anterior end with a small whitish patch. In comparison, A. laidlawi possesses a fairly prominent mid-dorsal keel, white mid-dorsal line, broad dark brown and irregular margin mid-lateral line, and whitish anterior and posterior ends of notum. In contrast, A. punctata has a fairly prominent mid-dorsal keel, light yellow mid-dorsal line, and a yellow notum with scattered black spots ( Collinge, 1902: pl. 5, figs. 49–52). Additionally, A. gravelyi possesses a prominent mid-dorsal keel, dark clove-brown mid-dorsal line, mid-lateral line with pale buff blotches above and clove-brown band below, upper part of mid-lateral line sepia with dark brown blotches and small spots, and lower part of mid-lateral line blue with slaty-black blotches and spots ( Ghosh, 1915: pl. 16, fig. 1). In addition, A. transversus , new species, possesses both left and right Simroth glands with curled cylindrical secretory part ( Fig. 5D). In comparison, A. laidlawi has left and right Simroth glands with an enlarged bulbous secretory part ( Fig. 5C), while A. gravelyi possesses only the right Simroth gland with a very slender secretory part ( Ghosh, 1915: pl. 19, fig. 27).

Although Atopos transversus , new species, has notum colouration and cross-reticulated stripes remarkably similar to those of Atopos kempii Ghosh, 1913 View in CoL and Atopos aborense ( Ghosh, 1913) View in CoL from Abor Hills, India, this new species can be distinguished from the Indian species by having yellowish-brown to pale brown notum decorated with scattered blackish to brownish cross-reticulated stripes, a small whitish patch at anterior end, and pale yellow to off-white foot. In comparison, A. kempii View in CoL exhibits a light straw notum with scattered dark blue cross-reticulated stripes, minute dark blue dots in the interspaces of cross-reticulated stripes, and a light-yellow foot ( Ghosh, 1913: pl. 10, fig. 1); whereas A. aborense View in CoL possesses a sepia notum with blackish dots and cross-reticulated stripes, and a lamp-black foot ( Ghosh, 1913: pl. 13, fig. 1). Regarding the genitalia characters, A. transversus , new species, possesses both left and right Simroth glands, and the right gland is composed of three parts: evaginable part, interconnected duct, and secretory part ( Fig. 5D), whereas A. kempii View in CoL and A. aborense View in CoL have only a right Simroth gland that consists of an evaginable part and an elongated free portion (= indistinguishable between interconnected duct and secretory part). In addition, A. kempii View in CoL has an evaginable part that is slightly shorter than the penis, and a very long free portion, whereas A. aborense View in CoL possesses an evaginable part approximately the same length as the penis, and a short free portion ( Ghosh, 1913: pl. 12, fig. 27, pl. 13, fig. 10).

In addition, this new species also differs from Atopos semperi Simroth, 1891 View in CoL from the Philippines and Atopos leuckarti Simroth, 1891 View in CoL from Indonesia in having yellowish-brown to pale brown notum decorated with scattered blackish to brownish cross-reticulated stripes. In comparison, A. semperi View in CoL exhibits a yellowish-red notum with blackish-violet cross-reticulated stripes, while A. leuckarti View in CoL possesses a reddishyellow notum with blackish-red cross-reticulated stripes ( Simroth, 1891: pl. 37, figs. 1, 2). Furthermore, A. transversus , new species, has the right Simroth gland larger than the left gland, and the right gland has a short-interconnected duct and long cylindrical secretory part ( Fig. 5D), while A. semperi View in CoL possesses left and right Simroth glands of approximately the same size, and the right gland has a very long-interconnected duct and elongated bulbous secretory part ( Simroth, 1891: pl. 37, figs. 16, 20).

Remarks. Comparing specimens from the two localities, the notum and cross stripes of the new species have slightly different colours. Specimens from Montawa Cave ( Fig. 3A, C) possess a pale brown notum with brownish cross-reticulated stripes, whereas the specimen from Myin Ma Hti Cave (Pagoda) ( Fig. 3D) possesses a yellowish-brown notum with blackish cross-reticulated stripes, which we consider to be an intraspecific morphological variation.