Dieurostus dussumierii ( Duméril, Bibron & Duméril, 1854 )

Souza, Hugo Francisco De, Pavukandy, Umesh & Ganesh, S. R., 2024, On further specimens of Dussumier’s Mud Snake Dieurostus dussumierii (Duméril, Bibron & Duméril, 1854) with notes on its taxonomy, type material, and natural history (Reptilia: Serpentes: Homalopsidae), Zootaxa 5496 (2), pp. 261-272 : 263-266

Dieurostus dussumierii ( Duméril, Bibron & Duméril, 1854)

( Table 1 ; Fig.1–5 )

“ Eurostus dussumierii Duméril 1853 ” nomen nudum, no description

Eurostus dussumierii Duméril, Bibron & Duméril, 1854: 953

Hypsirhina dussumieri — Jan, 1863

Eurostus dussumieri — Boulenger, 1896

Enhydris dussumieri (Smith) — Parameswaran 1954, 1962 (sic)

Enhydris dussumieri — Gyi 1970; Murphy 2007

Enhydris dussumierii — Smith 1943 (incl. H. malabarica ; read below)

Enhydris dussumierii — Kumar & Captain 2011; Chandramouli et al. 2012

Dieurostus dussumierii — Berg 1901

Dieurostus dussumieri — Kumar et al. 2012; Murphy & Voris 2014

Dieurostus dussumierii — Wallach et al. 2014; Ganesh et al. 2019

Hypsirhina malabarica Werner 1913: 26 (fide Smith 1943)

Hypsirhina melabarica Werner — Gyi 1970 (in error)

Material Examined (n=11). CES/S-523, CES/S-524, both juvenile females, CES/S-525, subadult male, CES/S-526, CES/S-527, both adult females, CES/S-528 an adult male, CES/S-529, CES/S-530, CES/S-531, CES/S-532, all adult females, coll. Hugo Francisco de Souza and Umesh Pavukandy in February 2022, all from Kumarakom near Vembanad Lake, Kottayam district; TNHM (H) 149, adult male, labelled “ Hypsirhina sp. ” coll. 14 July 1914 from Kulathupuzha , Kollam district, Kerala state, India .

Description and Variation ( Table 1 ). Body rather short and stout; body slightly depressed; snout fairly rounded; eyes and nostrils placed dorsally; Measurements (in mm): head length 11.1–38.7; head width 5.4–25.1; head depth 4.1–14.4; maximum body width 6.3–29.5; snout to vent length 175.0–745.0; tail length 22.0–95.0; relative tail lengths 10.60–11.50% (n=3, males), 13.00–14.80% (n=8, females); eye diameter 1.1–3.3; inter-orbital distance 3.1–9.5; inter-narial distance 1.7–3.7; rostral length 0.5–2.9; rostral width 1.0–5.0; internasal length 0.8– 2.3; internasal width 1.0–2.8; supraocular length 1.3–4.9; supraocular width 0.9–4.0; frontal length 2.8–6.9; frontal width 1.7–3.8; prefrontal length 1.3–3.8; prefrontal width 1.5–4.0; parietal length 2.8–9.5; parietal width 2.1–5.9; eye-snout tip distance 2.4–8.8; eye-lip distance 1.5–4.9; eye-nostril distance 1.7–5.9; nostril-snout tip distance 1.2–2.9; nasal length 1.3–3.8; nasal width 1.3–3.9; loreal length 0.6–3.9; loreal width 1.0–2.9; preocular length 0.8–1.6; preocular width 1.2–3.8; postocular length 1.0–2.8; postocular width 1.0–2.7. Scalation: Rostral visible from above; nasal pierced by nostril, with a nasal cleft; internasals or rather postnasals 2, touching one another; prefrontals 2; frontal longer than broad; loreal 1, touching 2 nd supralabial; parietals twice as long as broad; occipital small, rhomboid; preocular usually 1, rarely 2; preocular touching 3 rd supralabial; postoculars 2, basal one larger, touching 5 th supralabial; anterior temporal hexagonal, as large as loreal and basal postocular; anterior temporal 1; posterior temporals 2–3; basal one shortly contacts 6 th supralabial while the upper one contacts parietal; supralabials 7–8 (4 th –5 th touching eye), higher than broad; 6 th supralabial largest, hexagonal, bulged, contributing to the head height / depth, 7 th and 8 th ones often horizontally divided into upper and lower; infralabials 11–12 (5 th –7 th touching genials), progressively smaller, 1 st crescentic, oriented towards anterior genials; posterior genials much smaller than anterior pair; linguals 8–9; preventrals 2–3; ventrals 141–151, mildly angulate laterally, narrow; coastals rhomboid, homogenous throughout, two outermost scale rows slightly larger; coastals smooth, not imbricate, glossy; dorsal scale rows: 27 (neck): 27 (midbody); 23 (tail base); anal undivided; subcaudals 28–43 pairs, divided. Colouration: Dorsum olivaceous to greenish-brown, from 5 th /6 th to 19 th /21 st scale rows; three black parallel longitudinal stripes from parietals to tail-tip; vertebral stripe on 13 th scale row; lateral ones occupying 5 th –7 th scale rows on either side; ventral colour dirty white to golden orange, with three longitudinal parallel black stripes along the length of body; ventral stripes created by a central black patch on each consecutive ventral scales; this patch again bordered by another ventrolateral stripe of same colour, thickness, and length along upper edges of last coastal scale row; scales on head and neck bordered with light outline; ventrolateral scales bordered with dark edge; eye with golden ochre iris and round pupil.

Natural History observations. The present study was carried out in Vembanad wetland and the surrounding village of Kumarakom in Kerala. The study site adjoins a water bird heronry and our sampling was focused on the seasonal wetlands surrounding tourist hotels and backwater boat routes. Despite locals familiar with snakes reporting that this species was common in the area, we could only sight one individual on 29 th January. During the course of our intensive sampling, we observed four sightings of the homalospid Cerberus rynchops (Schneider, 1799) and, on average, six sightings of the natricid Fowlea cf. piscator (Schneider, 1799) per night.

On the 3 rd of February, local farmers informed us that they would begin tilling their fields in preparation for paddy sowing the following day. During this work, we encountered two individuals of D. dussumierii , one of which slithered into a pond that the farmers cordoned off for us. When we took a closer look at the other individual, it had succumbed to inadvertent spade wounds sustained during the digging process by the farmers. We suspended the following morning’s (4 th February) routine fieldwork and instead joined the farmers in their digging. Between 6 a.m. and 1 p. m., we encountered 26 individuals of D. dussumierii , most of which were hidden under 0.7–1.2m of paddy muck. Individuals of all life stages (neonate, juvenile, subadult, adult) and both sexes were recorded. Still, only the adults were observed to be actively hunting catfish that co-inhabited their ponds. Of the 26 encountered individuals, 14 were inadvertently hurt by the digging activity carried out by the farmers. We rescued and subsequently released four individuals that sustained rather minimal wounds and were expected to recover well in due course. However, the rest were either found dead or died soon after sighting, and hence were preserved for vouchering in museum collections for our studies.

During the times when D. dussumierii was seen, the overhead cloud cover was generally minimal, with intermittent haze during the night and early morning sampling. Short downpours during sampling were recorded on 26 th January and 1 st February. In the study area, generally, salinity readings varied between 0.4 and 4.1 parts per thousand (ppt). All individuals of D. dussumierii were found in water or under the soil with between 1.22 and 1.97 ppt. Air temperature varied between 23.7°C and 36.8°C during the sampling session, and all sightings of D. dussumierii were found in sites that experienced temperatures ranging between 29.2°C and 36.4°C. In the study area, water temperature varied between 26.1°C and 35.1°C during the sampling session, and all sightings of D. dussumierii were found in sites that experienced temperatures ranging between 28.7°C and 34.3°C.

MaxEnt Modelling ( Fig. 5 ). Our mapping and MaxEnt analysis revealed that low elevations (<50 m asl) areas in the coastal plains of central and southern Kerala, are the most suitable habitat / region within the realised range of D. dussumierii . The analysis run based on 40 points, including recently reported and the current study’s ones revealed fairly high projections (> 61%; dark grey shade) along the coast, while moderate projections (45–63%; light grey shade) in the immediately adjacent inland areas and low (15–45%; ash shade) to very low (<15%; halfwhite shade) projections in areas further inland, abutting the Western Ghats. No other part of the country (including Bengal) was projected as even very low suitable area for D. dussumierii (not shown).

Figures

FIGURE 1. Dieurostus dussumierii a syntype MNHN-RA-0.3751 (a) lateral, (b) dorsal and (c) ventral head profiles, (d) dorsal and (e) ventral entire body views. Photo courtesy MNHN; (f) modified reproduction of drawing from Duméril et al. (1854) showing entire ventrolateral view, head dorsal scalation and (inset) disarticulated skull and jaws.

FIGURE 2. Dieurostus dussumierii CES/S-529–32 (a) dorsal views, (b) CES/S-530 dorsal entire view, (c) dorsal and (d) ventral views of CES/S-523–25 young ones, (e) CES/S-527 and (f) CES/S-528 showing two preoculars.

FIGURE 3. Dieurostus dussumierii (a) close-up views of trunks of snakes injured unwittingly during farming, (b) live adult restrained in-situ, (c) live adult emerging out from paddy muck, (d) field dug out and worked by peasants and a live snake crawling out to slither away.

FIGURE 4. Dieurostus dussumierii century-old, historical specimen TNHM(H) 149 (a) entire dorsolateral view, (b) entire ventrolateral view, (c) head lateral view, (d) head dorsal view, (e) head vental view and (f) subcaudal profile.

FIGURE 5. Dieurostus dussumierii MaxEnt modelling map with localities dotted, wherein increasingly darker intensity blackish shade (darkest> 60%; lightest <15%) indicate higher simulated projection values and hence higher likelihood of occurrence.