Myrrophis dakkrongensis, Nguyen & Le & Lathrop & Vo & Murphy & Che, 2024

Nguyen, Sang Ngoc, Le, Manh Van, Lathrop, Amy, Vo, Thi-Dieu-Hien, Murphy, Robert W. & Che, Jing, 2024, A new species of mud snake (Squamata: Homalopsidae: Myrrophis) from southern Vietnam, Vertebrate Zoology 74, pp. 221-233 : 221

Myrrophis dakkrongensis sp. nov.

Holotype.

ITBCZ 6695, adult male, collected from Quang Son, Dak Glong District, Dak Nong Province, Vietnam; coordinates 12°10′24″N, 107°46′36″E; elevation 890 m a.s.l. by Sang N. Nguyen, on 3 August 2018 (Figs 2 , 3 , 5 ).

Paratypes.

Two specimens: ITBCZ 6694 (gravid female) and ITBCZ 6700 (adult male), also collected from Quang Son by the same collector. The former was collected on 2 August 2018 at coordinates 12°10′22″N, 107°46′20″E and elevation 890 m a.s.l. The latter was collected on 12 August 2018 at coordinates 12°09′22″N, 107°46′56″E and elevation 870 m a.s.l. (Figs 4 , 5 ).

Diagnosis.

Myrrophis dakkrongensis sp. nov. is distinguished from all of its congeners by the unique combination of the following morphological characters: medium-sized mud snake (largest TL 452 mm in adult female); internasal single and not in contact with loreals; dorsal scale rows 23-23-19 or 23-23-20, smooth; tail short (TaL/TL ratio 0.15-0.16 in males and 0.14 in female); ventrals 134-138 in males and 133 in female; subcaudals 39-42 in males and 34 in female; 8 supralabials, fourth entering orbit; second pair of chin-shield small, oblique, and in contact with two infralabials; 17 or 18 maxillary teeth; hemipenis short, forked and spinose, reaching 7th subcaudal; cloacal plate divided; gland-like tubercles present in the cloacal region; dorsum dark brown to black; and white or yellow to orange lateroventral stripe present.

Description of holotype.

Adult male; head elliptical in dorsal view, slightly distinct from neck; body short and cylindrical; SVL 372 mm; tail 70 mm (TaL/TL = 0.16); eye small, pupil vertically elliptical to round, situated on latero-dorsal side of the head; nostril directed upward.

Dorsal head scales smooth, slightly overlapping (Fig. 3A ); rostral broader than high (width 3.6 mm, height 1.8 mm), narrowly visible from above, touching nasals and 1st supralabial on both sides; nasals enlarged, more or less pentagonal, broadly in contact with one another behind the rostral; lateral nasal cleft distinctly sunken and extending to first labial, posterior nasal cleft shallow and extending to internasal; internasal single, lozenge-shaped, broader than long (width 2.5 mm, length 2.1 mm), not in contact with loreals; prefrontals forming median suture, in broad contact with nasals; frontal elongated, shield-shaped, almost twice as long as broad (width 2.6 mm, length 5.0 mm), almost as long as distance from tip of snout, and shorter than parietals; parietals in contact with each other behind frontal, each bordered laterally by upper temporals and anteriorly by frontal, supraocular and upper postocular; loreal single, longer than high and in contact with three first supralabials; preocular 1/1; postoculars 2/2, upper higher than long, lower longer than high; anterior temporal 1/1, posterior temporals 2/2, tertiary temporals 3/3; supralabials 8/8, 4th bordering eye, 4th-7th largest, 8th smallest; infralabials 11/11, first pair medially in contact with each other, first four in contact with anterior chin-shield, 4th and 5th in contact with posterior chin-shield, 6th largest; anterior chin shields much longer and wider than posterior ones (length 3.9 mm vs. 2.5 mm, width 1.8 mm vs. 1.1 mm), anterior pair in contact with each other; posterior pair small, oblique, separated from each other by two small scales, and in contact with two infralabials (Figs 3B , 5A ); six gulars and two preventrals between anterior chin-shield and 1st ventral.

Dorsal scales smooth, in 27 rows at first ventral, 23 rows at one head length behind head, 23 rows at midbody, 20 rows at one head length prior to vent, and 19 rows at third ventral anterior to vent; vertebral scale row same size and shape as other dorsal scales; dorsal scale row reduction from 23 to 21 at ventrals 87-92 by fusing 4th and 5th rows of body scales on both sides and from 21 to 19 at ventrals 122-126; ventrals 134 (plus two preventrals), broad, not keeled; cloacal plate divided; three gland-like tubercles on lateral sides of cloacal region (Fig. 3E ); subcaudals 42, all paired; terminal caudal scale forming a pointed cap.

Maxillary teeth 17, forming two groups separated by small diastema: anterior group with 15 teeth, strongly reflected backward; posterior group with two grooved teeth (Fig. 3F ).

Hemipenis short and spinose, extending to 8th subcaudal and forked at 4th subcaudal, having three main distinct areas: basal part naked, median part with enlarged curved spines, and distal part with two lobes bearing small and blunt spines. Bifurcate sulcus spermaticus moderately prominent and divided on two lobes.

In life, dorsal and lateral parts of body and tail dark brown; a distinct yellow to orange lateroventral stripe extending from neck to cloacal region, formed by upper half of first dorsal scale row, second dorsal scale row, and lower half of third dorsal scale row (Figs 2 , 3 ); venter cream to yellowish with three dark brown longitudinal stripes: two outer stripes occupy lower half of first dorsal scale row and outer margin of ventral; middle stripe at the center of each ventral. In preservation, color faded but pattern remains, with dorsal and lateral parts black; all yellow and orange parts becoming white or cream.

Variation.

Paratype ITBCZ 6700 has black dorsum and nasal cleft extending to loreal on both sides. Paratype ITBCZ 6694 has grey dorsum, white lateroventral stripe at the upper half of the first dorsal scale row and the lower half of the second dorsal scale row, and black ventral scales with white color on the posterior margin forming two bright longitudinal stripes. The enlarged, gland-like tubercles in cloacal region in this female are indistinct. Little variation occurs in size and scalation of the type series (Table 3 ).

Sexual dimorphism.

Males (n = 2) have marginally longer tails than the female (n = 1) (TaL/TL 0.15-0.16 in males; 0.14 in females) and more subcaudals (SC 39-42 in males, 34 in female). Males have distinct gland-like tubercles on lateral sides of the cloacal region, whereas this character in the sole female is indistinct.

Etymology.

The specific epithet dakkrongensis is a toponym derived from the Dak Krong River system where the new species was discovered. We recommend "Dak Krong mud snake" and "Rắn bồng đ ắk krông” as the common English and Vietnamese names of the new species, respectively.

Distribution.

The new species is currently known only from its type locality in Dak Glong District, Dak Nong Province, Vietnam (Fig. 6 ).

Field notes.

The holotype was collected at night when it was moving on the ground in a rubber plantation after a heavy rain (Fig. 4D ). The paratypes were collected in the daytime in a fishing net of local people set in a wetland in forest (Fig. 4E ). Paratype ITBCZ 6694 bears 12 well-developed embryos.

Comparisons.

Myrrophis dakkrongensis sp. nov. differs from all species in the family Homalopsidae , except for members in the genus Myrrophis , by the following unique combination of morphological characters: (1) open-grooved fangs on rear of maxillary bone, (2) rostral without appendages, (3) ventral scales wider than dorsal scales, (4) nasals in contact with each other, (5) dorsal scales smooth, in 23 rows at midbody, (6) first supralabial in contact with loreal, (7) internasal not in contact with loreal, and (9) white or yellow to orange stripe on dorsal scale rows 1-3 only ( Murphy and Voris 2014; Köhler et al. 2021). Myrrophis dakkrongensis sp. nov. differs from Myrrophis bennettii by having more dorsal scale rows at midbody (23 vs. 21), more dorsal scale rows before vent (19 or 20 vs. 17 or 15), fewer ventrals (133-138 vs. 158-169), and fewer subcaudals (34-42 vs. 45-56) ( Pope 1935; Smith 1943; Murphy and Voris 2014); and from Myrrophis chinensis by having more maxillary teeth (15 or 16 + 2 vs. 12 or 13 + 2), the second pair of chin shields small, oblique, and in contact with two infralabials (vs. large, longitudinal, and in contact with 3-4 infralabials) (Fig. 5 ), and absence of a dorsal pattern (vs. dorsal pattern of black dots arranging in longitudinal series and tending to be concentrated along the middle of the back and on either side of the body) ( Boulenger 1896; Pope 1935; Bourret 1936; Smith 1943; Kumar et al. 2012; Murphy and Voris 2014).

Figures

Figure 2. Holotype of Myrrophis dakkrongensis sp. nov. (ITBCZ 6695) in life.

Figure 3. Holotype of Myrrophis dakkrongensis sp. nov. (ITBCZ 6695). A - C Dorsal, ventral, and lateral views of head, respectively; D ventral view; E cloacal region showing three yellow gland-like tubercles on both sides; F lateral view of right maxillary teeth.

Figure 4. Paratypes of Myrrophis dakkrongensis sp. nov. and habitats of the new species. A Paratype ITBCZ 6694; B, C paratype ITBCZ 6700 and its hemipenes; D rubber plantation where the holotype was collected; E wetland in forest where paratype ITBCZ 6700 was collected.

Figure 5. Ventral view of heads of Myrrophis dakkrongensis sp. nov. (A, B) and Myrrophis chinensis (C, D) showing difference in the second pair of chin shields (highlighted). A Line drawing of head of the holotype ITBCZ 6695; B paratype ITBCZ 6700; C line drawing of head of Myrrophis chinensis (re-drawn from Boulenger 1896); D examined specimen ROM 31031. Scale bar 5 mm.

Figure 6. Distribution of homalopsid snakes in the genera Gyiophis, Myanophis, and Myrrophis in Indochina and southern China. Data taken from Zhao (2006), Murphy (2007), Karns et al. (2010), Kumar et al. (2012), Quah et al. (2017), Huang (2021), and Koehler et al. (2021).