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Zamenis scalaris (SCHINZ, 1822)

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Higher TaxaColubridae, Colubrinae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common NamesE: Ladder Snakes
G: Treppennatter
D: Trapslang 
SynonymColuber scalaris SCHINZ 1822: 123
Rhinechis agassizii
Xenodon Michahelles SCHLEGEL 1837: 92 (fide DUMÉRIL & BIBRON 1854)
Rhinechis scalaris — DUMÉRIL & BIBRON 1854: 227
Coluber scalaris — BOULENGER 1894: 65
Coluber scalaris — BOULENGER 1913
Elaphe scalaris — KAHL et al. 1980: 227
Elaphe scalaris — ENGELMANN et al 1993
Elaphe scalaris — SCHULZ 1996: 229
Rhinechis scalaris — HELFENBERGER 2001
Rhinechis scalaris — UTIGER et al. 2002
Rhinechis scalaris — AGUILAR 2005
Rhinechis scalaris — VENCHI & SINDACO 2006
Rhinechis scalaris — GRUBER 2009
Rhinechis scalaris — PYRON et al. 2011
Zamenis scalaris — ZAHER et al. 2012
Rhinechis scalaris — SINDACO et al. 2013: 135
Rhinechis scalaris — KWET & TRAPP 2015
Zamenis scalaris — WALLACH et al. 2014: 809
Zamenis scalaris — FIGUEROA et al. 2016
Rhinechis scalaris — DIECKMANN 2018
Zamenis scalaris — SALVI et al. 2018
Zamenis scalaris — SPEYBROECK et al. 2020 
DistributionSpain (except for the North, introduced to Menorca, Ibiza), Portugal, Gibraltar, S France

Type locality: S France (Schinz, 1822)  
TypesType: nondesignated, location unknown (fide V. Wallach, pers. comm.) 
DiagnosisDiagnosis (genus): The only external feature that differentiated the genera Rhinechis and Zamenis is the rostral shield (Boulenger, 1894; Venchi & Sindaco, 2006). In R. scalaris the rostral shield forms an acute angle posteriorly, clearly pointing behind and wedged between the internasal scales, which represents a unique trait in ratsnakes (Boulenger, 1894, Salvi et al. 2018).

Description: 2 dark longitudinal lines along the sides of the back on a pale, yellowish or reddish-brown background. A series of loose irregularly spaced small, vertical, black marks on the flanks tend to disappear with age, sometimes leaving just an indistinct longitudinal band on either side, making 4 longitudinal bands in all.There are a few black marks on the top of the head, at the edges of the head scales, that tend to disappear in the adult. On the side of the head, there are a few incomplete black bars on the labials, a black mark below the eye and a wide black oblique temporal band that ends at the corner of the mouth. These also fade in the adult and disappear in certain aged individuals, especially males.
Eyes have black irises; the pupil is hardly distinguishable. Smooth and shiny back scales, generally arranged in 27 (sometimes 25 or 29) rows at mid- body.The rostral plate is remarkably pointed and predominant, protruding farther than the lower mandible, especially in adults, and is inserted in a point between the internasals; 1 large preocular, 2 postoculars, 7-9 supralabials on each side, the 4th and 5th in contact with the lower edge of the eye. 198-228 ventral plates, a divided anal plate (Geniez 2018: 181).

Sexual dimorphism: males have yellowish colouring on the sides of the head and neck, whereas females partially retain their juvenile colouring (but not transverse bars on the back) (Geniez 2018: 181).

Ontogenetic change: The juveniles have a very contrasting black on straw-yellow or very pale beige pattern, the black in the form of successive Hs joined together to form a ladder.The ladder bars progressively disappear as the snake ages, eventually leaving just 2 dark lines; the belly becoming a uniform pale yellow. See also description (Geniez 2018: 181). 
CommentDistribution: Might occur in Morocco (fide JOGER 1983). Listed as questionable for Italy by Geniez 2018 (only ONE specimen found in Liguria, possibly introduced from France? [E. RAZZETTI, pers. comm.]). For a map see Sindaco et al. 2013.

Type species: Rhinechis agassizii (= Rhinechis scalaris) is the type species of the genus Rhinechis MICHAHELLES in WAGLER 1833.

Synonymy: Rhinechis is nested within Zamenis in several studies (reviewed by Salvi et al. 2018) including Zaher et al. 2012 (Appendix S1) who do not recommend any taxonomic changes. WALLACH et al. 2014: 809 synonymized Rhinechis with Zamenis. However, with an extended dataset Salvi et al. 2018 found Rhinechis and Zamenis to be monophyletic each.

Behavior: Geniez (2018) says that the snake is “quite lethargic” but some reports found the species to be rather aggressive (e.g. R. Leye, pers. comm., 21 Jan 2021). 
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