Xenochrophis piscator ( Schneider, 1799 )
treatment provided by
|Xenochrophis piscator ( Schneider, 1799 )|
Hydrus piscator Schneider, 1799: 247 ; based on Russell (1796: 38, pl. 33, “Neeli Koea”).— Type locality by original designation:
“ Indiae orientalis ”, namely Eastern India; here restricted by geographic inference to the northern coastal areas of Andhra Pradesh
State, eastern India.— Holotype. BMNH 1904.7.27.32. Coluber anostomosatus Daudin, 1803 . Coluber umbratus Daudin, 1803 . Hydrus palustris Schneider, 1799 . Coluber braminus Daudin, 1803 . Coluber mortuarius Daudin, 1803 . Coluber dora Daudin, 1803 . Coluber bengalensis Gray, 1834 . Coluber rectangulus Gray, 1834 . Tropidonotus quincunciatus Schlegel, 1837 . Tropidonotus sancti-johannis Boulenger, 1890 . [ Tropidonotus piscator ] var. unicolor Wall, 1907 . [ Tropidonotus piscator ] var. lateralis Wall, 1907 . [ Tropidonotus piscator ] var. punctatus Wall, 1907 . [ Tropidonotus piscator ] var. obscurus Wall, 1907 .
Taxonomic comments. Initially, our revision suggested that the taxonomy of this species was unresolved. We are convinced that several taxa remain under this nomina. Because the boundaries of these taxa cannot be resolved at the moment, we do not list those populations here and combine them under the name X. piscator . The exceptions are the Sri Lankan population and the northern Indian X. sanctijohannis . Although we do not formally recognize these two taxa as specifically distinct from X. piscator pending further research on the X. piscator -group, we treat both of them separately. The Sri Lanka population, as an insular form, is defined through the geographical barrier (Palk Straits). Due to the fact that it is distinguishable by pholidosis, we feel that it is useful to treat it separately. Xenochrophis sanctijohannis is mainly defined by its colouration. Because it was treated as a full species by recent authors, we also treat it here separately, and description is given below. As a consequence, the specimens from these two groups are excluded from the diagnosis of X. piscator given here.
Identification. Body cylindrical, moderately stout in males, very stout in old females; tail length unexceptional. Maximum recorded total length 1,020 mm for female (MNHN 1991.1628 from Bengal). Males barely shorter (maximum length females / males 1.03), largest male total length 992 mm (BMNH 184.108.40.206 from Bombay). Tail 28.3–33.1 % of total length in males 24.7–30.0 % in females, with sexual dimorphism. Head distinct from neck, eye size average or large, i.e. diameter equal to or greater than distance between edge of upper lip and lower margin of eye.
Dorsal scales in 19–19–17 rows (21–19– 17 in 4 specimens, 19–19– 16 in one specimen), weekly keeled, except the outer two to four rows; vertebral scales not enlarged. Ventral scales: 128–143 in males and 136–154 in females, unkeeled; subcaudals: 79–96 in males and 68–88 in females, unkeeled and paired; anal plate divided. Head scalation includes 1 loreal, 1 preocular, 3 or sometimes 4 postoculars, 2 (sometimes 3 rarely 1 or 4) anterior temporals, and 2 (sometimes 3 rarely 1) posterior temporals, 9 supralabials (in four cases 8, in one case 10) with 4 th to 5 th (rarely only the 4 th in one case only the 5 th) contacting eye, 10 (rarely 9 or 11) infralabials, with anteriormost 5 (in three cases 6) touching anterior chin shields.
Dorsal colour highly variable, glossy olive green, olive brown, tan, yellowish-grey, brown, grey or blackishbrown. Dorsal pattern also variable, in part correlated to geographical variation. Some individuals almost uniform, but dorsal pattern normally consists of five to seven rows of dark brown, dark grey or black blotches, alternating to give chess-board like pattern. Amount of rows might vary at different levels of body; most prominent anteriorly and vanishing posteriorly. Size of blotches extremely variable: they might be so large and confluent, that the body looks nearly black with small pale dots. In contrast, blotches may be also reduced to small dots; usually, the outer row larger than the other two ones, forming short transverse bars; some specimens speckled, spotted or blotched with white dots, sometimes in hues of reddish-brown that may also vary from salmon or rose pink to a brilliant scarlet and also varies in abundance; speckling irregularly distributed across the dorsum, but almost entirely confined to ventral half of each scale and especially their margins, where scales overlap one another. Lastly, some pale, large diffuse blotches usually present on the sides between the dorsal black blotches, especially in specimens where dark blotches are narrow.
Two oblique black lines extend on each side of the head, one below the other behind the eye. There might be two pale, dark-edged ocelli, on parietals (visible in 105 out of 130 specimens). Behind parietals, often a pale, darkedged mark that might extend into neck mark and breaking it (83 out of 130 specimens). On the neck, there is a either a dark mark looking from above as an inverted V (apex towards the snout) (in 78 out of 130 examined specimens) or no mark at all ( Wall, 1907; Taylor, 1965; own data). This inverted V or the lack of nuchal mark easily separate X. piscator from X. flavipunctatus . Venter cream or yellowish-brown, all ventral plates with cloudy spots laterally. Throat and forebody may be bright yellow or orange ventrally.
Morphological variation. Specimens from northeastern India have large dark checker-board blotches with a strong contrast. They attain a much larger size and might warrant a distinct specific status in the future. Our data are insufficient at the moment to prove this, but we regard it as likely. For this population the name X. mortuarius ( Daudin, 1803) would be available (see above).
Some specimens from southern India have a broad straight collar marking. We believe this population also to be a distinct, valid species but again our data are insufficient to fully resolve this at the moment. For this population, the name Xenochrophis bengalensis (Gray, 1837) would be available. These specimens are not conspecific with X. schnurrenbergeri (see Table 3). We also examined pictures of a few specimens from southern India without any pattern. At the moment nothing can be said about the status of these animals.
Specimens form the eastern part of the range, namely from western Thailand and Laos, show some extreme values in numbers of ventrals and subcaudals, namely 130–136 VEN (n = 12) and 86–94 SC (n = 11) in males, and 136–145 VEN (n = 15) and 75–85 SC (n = 14) in females. They are at the lower end of the range of ventrals in contrast to very high counts in nearby Chinese populations. The subcaudals of hese Thailand and Laos specimens are at the upper end of the variation. They are also smaller (largest male 761 mm, largest female 890 mm) and inconspicuously coloured. This population might warrant specific status, too. No name is available for this population.
Distribution. This species, as defined here, has a wide range in subtropical and tropical Asia. Pakistan. Eastern and southeastern parts of the country. India. Throughout the country. Nepal. Southern edge, in the Terai. Bangladesh. Throughout the country. Myanmar. Throughout the country, except Tenasserim. Known only from the north, west and northwest of the country. Laos. Northwest, in the region of Vientiane and further west. People’s Republic of China. Only known from southwestern Yunnan Province and in western Guangxi Province.
The population here recognized as the “ X. sanctijohannis morph” is known from northern India, Nepal, Afghanistan (ZFMK H 8652) and northern Myanmar.
Discussion. Underwood (1948) discussed variation of 49 specimens of this species form Cocanada, Madras Presidency, India. In this sample, 19 specimens were freshly caught, and 13 and 17 neonates from two clutches laid by two females from the wild. His data are shown in Table 2.
The ventral counts given by Underwood (1948) are slightly above our values, perhaps due to differences in counting methods. All other data are inside our ranges. Underwood discusses variation in colouration and pholidosis in his specimens, a discussion of which is beyond the aims of this work.
As already noted above, Taylor (1965) compared some scale counts of X. piscator and X. flavipunctatus specimens from northern Thailand. For X. piscator , the variation in the numbers of ventrals of his females is 140– 144 (our data for the whole distribution 136–154), for his males 131–146 (our data 128–143). Taylor did not use Dowling’s method system, so his counts might be higher by about one to two scales. For the subcaudals, he gave 77–80 (our data 68–88) in females and 80–93 (our data 79–96) in the three complete males he had at hand. The relative tail length is 0.27–0.28 in females (0.25–0.30) and 0.29–0.30 in 3 males (0.28–0.33). Again, all of these data agree with our findings except one female which might have one ventral more than the maximum value given here, but because of the different counting methods we cannot judge if this specimen is within the variation shown by our sample. Taylor’s largest specimen was a female 1,108 mm long, which is larger than our largest female (1,020 mm).
Kramer (1977) provided data for 29 specimens from a single locality in Nepal. He provided the following scale counts (our values for the whole distribution area in brackets): ventrals males, n = 14, 133–141 (128–143), ventrals females, n = 15, 146–155 (136–154), subcaudals males, n = 9, 90–96 (79–96) and subcaudals females, n = 12, 78– 82 (68–88). The ventral counts for his females are on the upper limit or one scale above our range. The subcaudals for males are also on our upper limit; those for the females are high but below our upper limit. As might be expected, there is some geographical variation in the scale counts of X. piscator as defined here. Kramer stated that a neotype for this species should be designated. He called the population here defined as X. piscator “lowland form” and that of the higher elevations “highland form”. Kramer correlated the highland form with X. p. sanctijohannis . A discussion of this form is given below.
Lastly, Zug et al. (2006) reported data for 20 specimens from Myanmar. All of their values fit within the ranges of our data .
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.