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 : 550-553

Trachischium sushantai sp. nov.

( Figures 1 , 2 )

Holotype. ZSI25651A, National Zoological Collection , ZSI, Kolkata ; adult female; from ‘ Jammu’ ( Jammu & Kashmir state, India); collected on 4th August, 1993, during Jammu survey; name of collector is given in register as ‘ Rajtilok’.

Diagnosis. Trachischium sushantai sp. nov. can be diagnosed by a combination of the following characters: a single nasal and PF, SL (R/L) 6/6, post-ocular 1, DSCH:M: V 13:13:13; VEN 152; SC 23 pairs of which those on anterior half of tail are as long as wide and regular hexagon/ rhomboid shaped, TAL/TL ratio of 0.11, head and dorsum uniform dark brown, venter brown with cream or yellow border on the trailing edges of VEN and SC.

Etymology. The new species is named after Sushanta Kumar Das, father of the second author of present paper. He is an enthusiastic nature observer who have spent a significant amount of time of his life in forested areas of West Bengal ( India) and nurtured the same interest in the second author. The specific epithet, a patronym, is a noun in genitive case.

Description of holotype. Adult female; incised on underside; SVL and TAL of 276 mm and 35 mm respectively; tail small, TAL/TL ratio being only 0.11; head small (HL 7.8 mm, 2.8 % of SVL); head width (HW 4.7 mm) greater than head height (HH 4.2 mm); head indistinct from neck; eye small (ED 1 mm, 12.8 % of HL); ESN 2.9 mm; rostral slightly wider than high (1.1 mm and 0.8 mm, respectively); internasals paired, much shorter than the single PF; frontal pentagonal, 2.8 mm long, longer than its distance from the posterior edge of rostral (1.9 mm), around two and half times wider than supraocular; parietals, being 4.4 mm long, are longer than frontal; 1 pre- and 1 post-ocular; loreal nearly twice wider than high and is in contact with nasal, internasal, frontal, preocular and 1 st and 2nd SL; very small nostril in single forward directed nasal; SL (R/L) 6/6, 1 st smallest and 6th largest, 3rd and 4th touching eye; IL (R/L) 6/6, 1st, 2nd and 3rd IL touch the anterior genial while the 4th one contacts both the anterior and posterior genials; anterior genials longer than posterior genials; TEMP (R/L) 1+2/1+2; maxillary teeth in life were probably around 16 or 17 (counting for missing teeth which were evident by longer than usual gaps between extant teeth at some places), subequal; dorsal scales smooth, including those around the region of the tail base, DSCH:M: V 13:13:13; VEN 152; anal divided; SC 23 pairs, anterior subcaudals (those on anterior half of tail) are as wide as long (4SCW/L 1.05 and 5SCW/L 1.01), regular hexagonal or rhomboid shaped, SC become slightly wider than long on posterior part of tail; tail tip in a spike like scale.

Coloration in preservative: head and dorsum uniform dark brown; edges of scales on lower jaw lighter colored; venter brown with outeredges of VEN cream or dirty yellow; underside of tail light brown with the posterior edges of SC bordered with lighter yellowish cream.

Comparisons. T. sushantai sp. nov. differs from T. monticola in possessing 13 rows of dorsal scales (vs. 15 rows in the latter), undivided PF (vs. divided PF in T. monticola ), 1 post-ocular (vs. usually 2 in the latter) and 152 VEN (vs. less than 125 VEN in T. monticola [ Smith 1943])( Table 2).

T. sushantai sp. nov. differs from T. leave in having 6 SL, 1 PF, 23 SC and a brown venter (vs. 5 SL, 2 PF, 29– 39 SC and a yellow venter in T. leave ).

T. sushantai sp. nov. can be diagnosed from T. tenuiceps by having a shorter tail (TAL/TL 0.11), 1 PF, 1 postocular, 23 SC of which the anterior ones are regular hexagonal or rhomboid and a brown venter (vs. TAL/TL 0.15– 0.18, 2 PF and 2 post-oculars, 28–42 SC of which anterior ones are transversely elongated and yellowish or orange ventral coloration in T. tenuiceps ).

T. sushantai sp. nov. differs from T. guentheri by having a brown venter and 23 pairs of SC (vs. a coral red venter in T. guentheri and SC more than 30 in T. guentheri [ Smith 1943]).

The new species most closely resembles T. fuscum from which it can be distinguished by its shorter tail (TAL/ TL 0.11) compared to T. fuscum (vs. TAL/TL 0.13–0.18 [± 0.14 in 27 specimens] in T. fuscum ), 23 pairs of SC of which anterior ones are regular hexagonal/rhomboid with 4SCW/L 1.05 and 5SCW/L 1.01 (vs. 30–44 SC in T. fuscum [31–41 in females examined by us], SC wider than long and are not regular hexagonal/rhomboid with 4SCW/L 1.33–3 [± 1.6 in 22 specimens] and 5SCW/L 1.27–2.7 [± 1.6 in 21 specimens] in physically examined specimens [specimens of T. fuscum examined from photographs too had SC number within the range given here and were distinctly wider than long]).

Distribution. Trachischium sushantai sp. nov. is currently known only from its type locality in Jammu (Jammu & Kahmir, India) ( Figure 3 ).

Natural history. Unknown.

Figures

FIGURE 1. Holotype of Trachischium sushantai sp. nov.A. dorsal view of the head, B. lateral view of the head, and C. dorsal view.

FIGURE 2. A. Regular hexagonal/rhomboid subcaudals, anterior ones are as long as wide, in Trachischium sushantai sp. nov.in comparison to much wider than long subcaudals typical of B. and C. T.fuscum, D. T. guentheri. (Photo of Figure 2B by Aquila Wilks)

FIGURE 3. Map showing the type localities of Trachischium sushantai sp. nov. (large open circle), T. fuscum (small filled circle), T. rugosum (large square) and Ablabes gilgiticus (star). Larger symbols are used for those type localities which is the name of a large area i.e. recorded with lesser precision (for instance, exact collection locality within Jammu devision is not known for T. sushantai sp. nov.). Type localities of Eminophis lineolata and Calamaria obscurostriata are in all probability erroneous and therefore not shown.