Isthmura corrugata Sandoval-Comte & Pineda & Rovito & Luría-Manzano 2017, sp. nov.

Isthmura corrugata sp. nov.

Suggested English name: Corrugated Salamander. Suggested Spanish name: Salamandra corrugada. (Figures 2, 3)

Holotype. CARIE 0 943 (Colección de Anfibios y Reptiles del Instituto de Ecología, A.C.), an adult male collected 9 km NW of Coatepec, Veracruz, México (19° 29´N, 97° 02´W), 2,106 m elevation, collected by A. Sandoval- Comte (original field number ASC 200) at 22:15 h on 28 April 2014 (Fig. 2 A–2F).

Paratype. CARIE 0 960, an adult male, same locality data as the holotype, collected by R. Luría-Manzano at 15:18 h on 4 August 2014 (Fig. 2 G–2H).

Diagnosis. This is a plethodontid salamander of the genus Isthmura, based on its large size, robust body, and presence of a sublingual fold as well as on mtDNA sequence data. Differs from all other bolitoglossines except Pseudoeurycea papenfussi by its extremely well-defined and bulging costal folds, giving it a segmented appearance that extends even across the venter. Distinguished from all species of Aquiloeurycea by its larger size (A. scandens maximum SL 71 mm) and from similarly sized species of Bolitoglossa by the presence of a sublingual fold. Differs from large, robust species of Pseudoeurycea such as P. papenfussi and P. smithi by having more substantial foot webbing and triangularly shaped toes. It is the second smallest species of Isthmura (maximum SL 85.3 mm), only slightly larger than I. naucampatepetl (maximum SL 82.9 mm); all other species in the genus are substantially larger (maximum SL in: I. sierraoccidentalis 88.3 mm; I. maxima 128.1 mm; I. bellii 146 mm; I. boneti 107 mm; I. gigantea 161 mm; Parra-Olea et al. 2005; Raffaëlli 2007). No females of I. corrugata have been found, so the maximum size of this species is likely greater than 85.3 mm SL because female Isthmura tend to be larger than males.

Members of the genus Isthmura have been characterized by the presence of spots or marks on a solid black dorsal background. The new species, however, is easily distinguished from all other members of the genus by the absence of any spot or mark on the dorsum, which instead is uniformly black, except by dull reddish brown coloration on eyelids. All other species have a series of chevrons (I. boneti and I. gigantea), half-chevrons (I. bellii and I. maxima), or small marks (I. naucampatepetl) along the dorsum, that are red-orange in all species except in I. naucampatepetl, in which they are pink (Parra-Olea et al. 2001; Parra-Olea et al. 2005). Isthmura sierraoccidentalis has a predominantly black dorsum, but all known individuals have some degree of reduced redorange dorsal spotting (Lowe et al. 1968; Rovito et al. 2015). Isthmura corrugata is further distinguished by contrasting coloration between the blackish brown dorsal and vinaceous brown ventral background color, whereas all other species of the genus have a uniformly black dorsal and ventral background coloration. In addition, this species has a body marked by deep grooves and an unusual coloring above the eyes (dull reddish brown). Some body proportions also distinguish the new species from its congeners (Fig. 2). It has a relatively larger head (mean HL/SL= 0.23 versus 0.15–0.18 in the other species) and a relatively shorter tail (mean TL/SL= 0.69 versus 0.77– 0.98 in the other species).

Description of holotype. Among the large salamanders of the genus Isthmura, this is a robust but relatively small species (maximum SL= 85.3 mm). Its body has a very muscular appearance. It has a prominent, broad (HW/ SL= 0.22) and large head (HL/SL= 0.23) with very substantial jaw musculature. Deep postorbital groove extends from eye to end of jaw and continues to gular region. Snout is rounded and neck region is defined by deep groove behind head, slightly narrower than head. Parotoid glands are well developed and a large oval mental gland (mental gland width/HW= 0.39) was present in both specimens. Eyes are protuberant. Maxillary teeth 62 (31/31), premaxillary teeth 6, enlarged compared to maxillary teeth; vomerine teeth 46, arranged in two arcs (22/24) extending beyond outer margin of choanae; around 52 parasphenoid teeth arranged in two series as inverted “V” shape; nasolabial protuberances are poorly developed (Fig. 3). Extremely well-marked costal grooves 13, counting one each in axilla and groin (Fig. 2). Tail is relatively short (TL/SL= 0.69) and robust with basal constriction and tip rounded. Limbs are robust and relatively long (combined limb length/SL= 0.5). Digits are well defined, relatively short, stout and triangular. Digits in order of decreasing length III-II-IV-I on hands and III-IV-II-V-I on feet (Fig. 2 D). Phalangeal formulae 1-2-3-2 for hands and 1-2-3-3-2 for feet.

Coloration in life. Dorsum uniformly dark, color Vandyke Brown (282) from tail to head (including hands and feet). Prominent eyelids, jaw margins and gular surface pale Cinnamon-Rufous (31). Iris Raw Umber (280). Distal half of flanks dark, like dorsal coloration; proximal half Deep Vinaceous (248) extending to the venter and ventral side of limbs (Fig. 2 A–2F).

Coloration in alcohol. Coloration very similar to that in life. Dorsum, dorsal surface of head, trunk, limbs, and tail Dusty Brown (285). Eyelids Raw Umber (280), slightly darker than in live individuals. Jaw margins and gular region Dark Grayish Olive (245). Distal half of flanks same color as dorsum, proximal half Deep Vinaceous (248), extending onto ventral surface. Ventral side of the tail color slightly more grayish than rest of its dorsum. Underside of hands and feet paler than in life (Fig. 2 G–2H).

Measurements of holotype / paratype (in mm). Standard length (SL: distance from snout to posterior end of vent) 71.9/85.3; head width (HW) 15.8/17.7; head length (HL: snout to gular fold) 16.3/20.8; head depth at angle of jaw 6.8/7.9; eyelid length 5.3/6.2; eyelid width 2.9/3.5; anterior rim of orbit to snout 3.6/4.5; eye diameter 2.8/ 3.3; interorbital distance 4.5/5.0; snout to forelimb 21.2/27.4; internarial distance 4.5/5.5; intercanthal distance 4.8/ 5.6; nostril diameter 0.4/0.6; snout projection beyond mandible 1.5/1.5; snout to anterior angle of vent 65.9/82.1; axilla to groin 31.6/35.1; tail length (TL) 48.3/60.2; tail width at base 7.0/7.5; tail depth at base 8.9/9.8; forelimb length 16.2/20.0; hind limb length 20.0/25.7; hand width 5.9/6.5; foot width 7.5/8.7; length of the longest (third) toe 2.1/2.3; length of fifth toe 0.9/1.2; mental gland width 6.1/6.2; mental gland length 3.8/3.8; Numbers of teeth: premaxillary 6/10; maxillary 62/60; vomerine 46/42 (Fig. 3).

Distribution and Ecology. Isthmura corrugata is known only from the type locality, near the city of Coatepec in the mountainous region of central Veracruz (Fig. 4). This mountain range lies within the eastern portion of the Trans-Mexican Volcanic Belt. The vegetation at the type locality is cloud forest, characterized by the presence of tall trees that provide a high percentage of canopy cover, a deep layer of leaf litter (= 8cm), and a high density of bromeliads and epiphytes. The dominant tree species are Clethra mexicana, Hedyosmum mexicanum, Miconia spp, Platanus mexicana, Quercus spp, as well as tree fern species (García-Franco et al. 2008; Toledo-Garibaldi & Williams-Linera 2014). A frequent fog maintains high levels of humidity. The holotype was found active on the forest floor at night, whereas the paratype was encountered inactive under a layer of leaf litter (= 10 cm) during the day. Despite of I. corrugata has been found only in one locality, it is possible that this species may inhabit additional localities around Cofre de Perote extending to the Sierra Norte de Puebla near Cuetzalan, because a high proportion of the amphibian fauna is shared between these areas.

Six species of salamanders have been found in sympatry with Isthmura corrugata: Aquiloeurycea cafetalera, Parvimolge townsendi, Thorius pennatulus, Pseudoeurycea lynchi, Chiropterotriton chiropterus and Chiropterotriton sp. Most of these species are found in the leaf litter, except for the last three, which also use arboreal bromeliads.

Etymology. The specific epithet makes reference to the extremely pronounced grooves along the body, giving these salamanders a corrugated appearance.