IUCN threat status:

Critically Endangered (CR)

Comprehensive Description

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Description

Calotriton arnoldi is an aquatic endemic Iberian newt. The holotype has a snout-vent length of 58.64 mm. The maximum length for males and females is 102.25 mm and 102.62 mm respectively. The head is greatly flattened with the broadest part at the level of the eyes. The snout is blunt with convex sides when looking at the rosal view. The canthus rostralis is marked. The areas above the eyes are raised; their width is about the third of the distance between the two eyes. There are outstanding swellings present on the posterior sides of the head. The throat is posterior to the gular region. The body has oval cross-sections and some compressions that are dorsoventral. Its tubercles are tipped with widely distributed hard blunt spines on the dorsum that become smaller and more scattered on the head and flanks, scattered mainly between the vertical grooves. The caudosacral vertebrate has short, transverse processes that are not directed backwards. The cloacal swelling that is hemispherical with a sagittally lengthened opening where the grooves extend laterally. The female cloaca is cylindrical and is relatively narrow. The digits are not elongated and they are unwebbed. The tail is short (about 2/3 the snout-vent length) and it is strongly compressed on the side, very deep at the base, and tapers gradually to a blunt point (Carranza and Amat 2005).

Calotriton arnoldi is similar to Calotriton asper but mitochondrial DNA sequences differ and there are a few morphological and coloration differences, such as smaller size and fewer spiny-tipped tubercles on the dorsum in C. arnoldi. Calotrion asper also has a light and very thin brownish-orange stripe that extends from its base to the tip of its tail that is absent in C. arnoldi (Carranza and Amat 2005).

In life, the dorsum is dark and is a chocolate color with occasional light silvery-gold stippling on the sides. The pink-ivory throat is very light and is largely unspotted or has a lightly dark stippling. The venter is translucent and is a light ochre-brown color; it has dark markings that are the same color as the dorsum and has dark stippling on the sides. The cloaca has a bright reddish-orange tip. In preservative, it is a dark chocolate brown color the greyish tinge on the dorsum. The flanks and the tail sides have scattered, irregular, pale grey spots. Its underside is dark cream and is brighter under the tail. The belly is partly translucent with ambiguous dark markings on the side that consist of dark stippling. The throat has a large dark blotch and is posterior to the gular region. The throat, upper lip margins, underside of tail, and ulnar and palmar aspects of the limbs are immaculate and pale, and the tips of the digits are dark brown (Carranza and Amat 2005).

There is a variation in the pattern of the coloration of this species. The eastern population has irregular pale yellow spots on the trail and body flanks that are more abundant and apparent in post-meta-morphic newts than adults. The males of the western population have a whitish margin of snout. The pigmentation on the belly also displays slight variability that is most likely the result of individual variation and not seasonal variation (Carranza and Amat 2005; Valbuena-Ureña et al. 2013).

Calotriton arnoldi split off from Calotriton asper 1.1 - 2 million years ago during the Pleistocene. While their distribution ranges are only separated by 25 km, they have evolved independently ever since. Additonally, although there are still similarities in morphology and behavior between the two species, there have not been any signs of hybridization, likely because of geographic isolation (Valbuena-Ureña et al. 2013).

Calotriton arnoldi is named after Dr. E. N. Arnold who is a British herpetologist with a life-long dedication and contribution to herpetology, especially European herpetology. He also guided the senior author of the species authority paper (Carranza and Amat 2005).

Featured in Amazing Amphibians on 21 October 2013

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