Trachischium sushantai, Raha & Das & Bag & Debnath & Pramanick, 2018

Raha, Sujoy, Das, Sunandan, Bag, Probhat, Debnath, Sudipta & Pramanick, Kousik, 2018, Description of a new species of genus Trachischium with a redescription of Trachischium fuscum (Serpentes: Colubridae: Natricinae), Zootaxa 4370 (5), pp. 549-561 : 553-555

Redescription of Trachischium fuscum Blyth, 1854

( Fig. 4A )

Talukdar et al. (1980) designated ZSI7044 as the lectotype of Trachischium fuscum . They provided a redescription but it was brief and contained some ambiguous (such as number of VEN) and erroneous (namely SVL and TAL) information. Moreover, it lacked morphometric details and description of the novel characters used in this paper (such as 4SCW/L and 5SCW/L) used to separate T. sushantai sp. nov from T.fuscum . The aforesaid reasons necessitate the inclusion of a redescription of the lectotype of T. fuscum along with an analysis of variation in paralectotypes and non-type materials of T. fuscum .

Redescription was based on the lectotype of Trachischium fuscum (ZSI7044): Adult male; SVL 325 mm and TAL 52 mm (not 305 mm and 49 mm respectively as reported by Talukdar et al. [1980]); TAL/TL ratio is 0.14; head small (HL 9.8 mm, 3.2 % of SVL), wider than its height (HW and HH 6.6 mm and 5.1 respectively); head indistinct from neck; eye small (ED 1.3 mm, 13.3 % of HL); ESN 3.7 mm; rostral slightly broader than high (width and height of rostral 1.2 mm and 1.1 mm respectively); internasals paired, much shorter than the undivided PF; length of the pentagonal frontal shield (3.6 mm) greater than its distance from the end of rostral (1.9 mm), wider than supraoculars; parietals (length 5.6 mm) longer than frontal; 1 pre- and 1 post-ocular; loreal twice wider than high; nasals divided and very small; SL (R/L) 6/6, 1 st smallest , 6th largest, 3rd and 4th touching the eye; IL (R/L) 6/6 of 4 are in contact with the genials; anterior genials longer than posterior genials; TEMP (R/L) 1+2/1+2; dorsal scales smooth except those on the basal region of tail which are keeled, DSCH:M: V 13:13:13; VEN 156; anal divided; SC 35 pairs, those one anterior half on tail around twice wider than long with 4SCW/L 2.46 and 5SCW/L 1.88.

Blyth (1854) described the colour as follows ‘Of an iridescent dull black colour throughout, the ventrals slightly margined paler.’ Now the specimen has become uniformly brown, with paler margins at the trailing edge of VEN still being evident.

Variations. Range of morphometric and meristic data of paralectotypes and other non-type specimens of T. fuscum are presented in Table 1. Head and dorsal scalation in this species shows almost no variation except that in ZSI18693 there is only one 1 posterior TEMP on right side. Smith (1943) reported the range of VEN as 150–165 (the lowest VEN count reported by Sharma [2007] is 132 which is most probably erroneous). The highest VEN count made by us was 169 in ZSI19120. Range of SC reported by Smith (1943) was 28–42. In ZSI18679, there are 44 pairs of SC. ZSI7059 (collected from Darjeeling) exhibits several anomalous ventral scales ( Figure 4B ). In this specimen, split VEN, incomplete VEN and fused VEN are present sporadically among normal VEN. This anomaly results from abnormalities on vertebrae and ribs (e.g. Shine et al. 2005; Mebert 2011). This specimen also has divided PF. Wall (1909b) found one specimen from Darjeeling which got 9 of its anterior SCs undivided. We found undivided SC in three specimens, including one paralectotype (ZSI7051). The dorsum coloration (in preservative) varies from dark brown to almost jet black. Juveniles, as reported by Wall (1909b) and Smith (1943), have longitudinal stripes and an incomplete collar over nape.

Here we would like to mention that there is another specimen from Jammu deposited in ZSI general collection (ZSI25651B) with divided nasal, VEN 150, SC 35 (first 4 undivided, rest distinctly wider than long, not regular hexagon/rhomboid shaped), SVL 227 mm and TAL 45 mm (TAL 19.8 % of SVL) and black dorsum. It can be seen that this specimen can be easily distinguished from the holotype of T. sushantai sp. nov. and we currently refer it to T. fuscum as we could not find any differences in characters from other T. fuscum of eastern Himalaya that we have studied.

Distribution. T. fuscum was found from the states of Jammu & Kashmir, northern West Bengal, Uttarakhand, Sikkim, Assam and eastern Arunachal Pradesh in India, east and central Nepal and Bhutan border area ( Günther 1860; Boulenger 1893; Annandale 1904; Wall 1909b; Smith 1943; Agarwal et al. 2010; Wallach et al. 2014; also see the references contained in Wallach et al. 2014). We currently regard one specimen from Jammu as T. fuscum . Also see comments on Ablabes gilgiticus . Wall (1924) regarded the locality Khasi hills (Meghalaya state) to be questionable.

Natural history. T. fuscum is a montane snake and it is found between 920 and 2590 meters above sea level ( Wallach et al. 2014). This snake species is semi-fossorial and live under stones and leaf litter in montane deciduous forests ( Wall 1909b; Das, 2002; Agarwal et al. 2010). Though Das (2002) stated that these snakes become active after sunset, Wall (1909b) frequently found it during daytime in Darjeeling. They feed on earthworms and are of very gentle disposition ( Wall 1909b). T. fuscum has a sex ratio that is skewed toward females. The specimens studied by us contained 14 males and 19 females (ratio 1:1.36). Wall (1909b) reported 37 males and 51 females among 88 specimens of which he determined the sex. A similar type of skewed sex ratio was reported for T. guentheri by Wall (1909b) and Chettri et al. (2009). The clutch size of T. fuscum was reported to be 3–6 ( Wall 1909b). We found 9 eggs in ZSI19120 (from Gopaldhara, Darjeeling, West Bengal) ( Figure 4C ). This is the highest number of eggs reported for any Trachischium spp. to date. Hatchlings of this species were seen by Wall (1909b) in Darjeeling in July.

Figures

FIGURE 4. A. Lectotype of Trachischium fuscum (ZSI7044), B. Anomalous ventrals of a T. fuscum (ZSI7059), C. Nine eggs in a specimen of Trachischium fuscum (ZSI19120)