Homalopsis nigroventralis Deuve, 1970

Murphy, John C., Voris, Harold K., Traub, Joshua & Cumberbatch, Christina, 2012, The masked water snakes of the genus Homalopsis Kuhl & van Hasselt, 1822 (Squamata, Serpentes, Homalopsidae), with the description of a new species, Zootaxa 3208, pp. 1-26 : 16-18

Homalopsis nigroventralis Deuve, 1970

Figs 2 d, 8d, 9

Homalopsis buccata — Taylor & Elbel 1958: 1159; Taylor 1965: 923; Gyi 1970: 136. Homalopsis buccata nigroventralis Deuve, 1970 . Type Specimen: none, Deuve’s specimens presumed lost in a fire. Type locality: Ngum River Valley, Laos.

Homalopsis nigroventralis Stuart et al. 2006:149 .

Comment. Deuve (1970) described this snake from the Ngum River Valley, Laos and reported 35–39 scale rows at midbody, 152–164 ventrals and 75–94 subcaudals. The specimens examined here fall within these parameters, except for the subcaudal counts. Homalopsis nigroventralis may use a different habitat than other Homalopsis – streams with a moderate current, and sand and rock substrate as opposed to slow moving or stagnant water with mud substrates. Because we have not examined specimens from Laos we have not established a neotype or restricted the type locality. Photographs of this snake can be found in Taylor & Elbel (1958: 1066) and Murphy (2007: 201-203). Field observations on this snake can be found in Deuve (1970), Stuart et al. (2006), and Bezuijen et al. (2009).

Diagnosis. Homalopsis nigroventralis has upper labials 1–3 contacting the loreal; two prefrontals; 35–39 dorsal scale rows at midbody, reduced to 30 or less; one or two postocular scales plus one postsubocular scale; 10–12 upper labials; 159–167 ventrals; and a reverse color pattern on the venter (dark olive-gray with white spots). Homalopsis buccata has upper labials 1–4 contacting the loreal; one postocular scale plus a postsubocular scale; a ventral pattern that is light with dark spots. Homalopsis hardwickii has a divided loreal contacting upper labials 1– 4; one postocular scale and no presubocular scale. Homalopsis semizonata has a divided or fragmented loreal contacting upper labials 1–4 or 1–5; three prefrontals; 39–44 dorsal scale rows at midbody, reduced to more than 30 posteriorly; one postocular and one postsubocular. The new species, H. mereljcoxi has a single loreal contacting upper labials 1–4; 40–47 scale rows at midbody, reduced to 30 or more posteriorly; 13 (12–14) upper labials; and ventral counts that are usually greater than 165.

Distribution. This species is known from the Mekong River in Laos, Cambodia, and Thailand. Deuve (1970) reported it in the Ngum River Valley of Laos. Taylor & Elbel (1958) describe specimens from Thailand’s Phan Phu Mountain, and Stuart et al. (2006) reported it from Siem Pang and Ta Veng in eastern Cambodia in bamboo mixed with evergreen forest between 100 and 170 m ASL. Two specimens were taken during the day, others were found in gill nets. The streams were described as having a moderate current, and a sand and rock substrate; one had a closed canopy, others were open and had grass lined banks. All of these localities are peripheral to the Mekong. However, Bezuijen et al. (2009) report it from the Mekong River in Kratie Province, Cambodia. They describe four specimens, one in a market, and three others at Koh Kapeung and Koh Khlap Islands, the largest was 104 cm in total length. One of these snakes was on a mud substrate.

Material Examined. CAMBODIA – Ta Veng FMNH 263029 (Virachey National Park, O Lopeung stream, 14°10'39.2" N, 107°17'25.1" E, 150 m); Siem Pang FMNH 263030 (Virachey National Park, O Kanome stream, 14°13'33.7" N, 106°36'16.0" E, 170 m), FMNH 2630301-32 (Virachey National Park, O Kanome stream, 14°15'08.0" N, 106°37'58.8" E, 175 m), FMNH 263033 (Virachey National Park, 14°12'53.8" N, 106°35'51.3" E, 100 m); Nong Khai FMNH 265801 (Phu Wua Wildlife Sanctuary, Houay Sod waterfall, 18°15'51.4" N, 103°54'22.1" E, 160 m), MNHN 1988.2104; THAILAND – Phan Phu Mt. FMNH 179239, 117858-60.

Figures

FIGURE 2. Plots of the principal components (PC) scores on the first two PC axes derived from 11 morphological variables (dorsal scale row counts on the forebody, midbody, posterior body; number of prefrontals, preoculars, postoculars, upper labials; upper labials under orbit; upper labials at loreal; loreal condition; ventral pattern) for 95 specimens of Homalopsis. The square with the central circle is H. hardwickii which associates with H. buccata in this analysis. Plot A compares H. buccata, H. mereljcoxi, and H. hardwickii; Plot B compares H. buccata, H. mereljcoxi, H. hardwickii, and H. semizonata; Plot C compares all five species: H. buccata, H. mereljcoxi, H. hardwickii, H. semizonata, and H. nigroventralis.