Paikwaophis kruki, Kok & Means, 2024

Kok, Philippe J. R. & Means, D. Bruce, 2024, Hiding in the mists: molecular phylogenetic position and description of a new genus and species of snake (Dipsadidae: Xenodontinae) from the remote cloud forest of the Lost World, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 200 (2), pp. 505-531 : 514-528

Paikwaophis kruki gen. nov., sp. nov.

Zoobank registration: urn:lsid:zoobank.org:act:A7918471-9399-4AEA-AD08-D176E13D53ED

Holotype: RBINS 2734 (field number CPI11310; Figs 4–13), an immature female, collected by D. Bruce Means on 24 February 2021 at ‘ Sloth Camp’ [5.247074° N, 60.705471° W; ~ 1180 m elevation; Cuyuni-Mazaruni District (Region 7), Guyana, South America], which is located on a broad ridge running downhill along the west fork of the Paikwa River from the bottom of the talus slope below the vertical cliff wall of Wei-Assipu-tepui ( Fig. 2).

Etymology: The specific epithet ‘ kruki ’ is a noun in the genitive case, honouring Professor Andrzej Kruk (born 1971), the current Dean of the Faculty of Biology and Environmental Protection at the University of Łódź, Poland, for his friendship and his influential contribution in enhancing the quality of research at the University of Łódź.

Diagnosis: The species diagnosis is the same as for the genus.

Description of holotype: The specimen is a small immature female ( Figs 4–13), with TL 180 mm, TaL 24 mm (13% of TL); HL 7.1 mm (4% of TL); HW 4.7 mm (66% of HL); snout short and blunt, SnL 2.1 mm (30% of HL); ED 1.0 mm; DSN 0.6 mm; and DNE 1.5 mm. Head poorly distinct from neck; body robust, slightly wider than high. Dorsal scales rhomboid, smooth, lacking keels or apical pits, DSR 17-17-17. There are 171 ventrals, an undivided anal scale and 38 paired subcaudals. Dentition diacranterian, aglyphous opisthodont. Prediastemal maxillary teeth 7, postdiastemal teeth 2.

Rostral 3.6 times wider than high (RW 1.8 mm, RH 0.5 mm), visible from above, contacting first supralabials, nasals and internasals. Paired internasals 1.3 times wider than long, laterally in contact with nasals. Paired prefrontals large, 1.5 times broader than long, laterally contacting nasals, second supralabials and preoculars. Frontal subtriangular, anteriorly convex, with dorsal termination acute, ~1.2 times longer than wide, laterally in contact with supraoculars, laterodorsally in contact with parietals. Elongate single supraocular ~2 times longer than wide. Parietals large, ~2 times longer than wide, median suture ~1.5 times shorter than frontal length. Nostrils located in anterior portion of undivided nasals, which are 2 times longer than high. Nasals in contact with rostral, internasals, first and second supralabials and prefrontals. Loreal absent, seemingly fused with prefrontal. Eyes moderate in size, with vertically oval pupils, poorly visible in ventral view, surrounded by one preocular, one supraocular, two postoculars and third and fourth supralabials. No subocular. Preocular ~2 times higher than long. Supralabials 7/7, with numerous minute sensory pits, irregularly increasing in size posteriorly; last one ~2 times longer, but as high as first; second supralabial contacting nasal, prefrontal and preocular; third contacting preocular and eye; fourth contacting eye and lower postocular; fifth contacting lower postocular and anterior temporal; sixth contacting anterior and lower posterior temporals; seventh contacting lower posterior temporal and first scale of dorsolateral and lateral body scale row. Temporals 1 + 2 + 3; first and second temporals about twice as long as high; third temporals almost as long as high. Mental triangular, as long as wide, separated from chinshields by first pair of infralabials, which are in contact with each other along the ventral midline. Infralabials 7/7, with numerous minute sensory pits; fourth the largest, second the smallest; first to fourth contacting anterior pair of chinshields (fourth in point contact); fourth infralabial contacting posterior chinshield and first gular. Two pairs of chinshields; anterior chinshields projecting frontolaterally, about twice as wide as long and ~1.6 times shorter than posterior chinshields; posterior chinshields ~2.5 times longer than wide, laterally contacting fourth infralabial, posteriorly separated from first preventral by two rows of gulars. Anterior row of gulars consists of six scales; second row consists of seven scales.

Summary of morphometric and meristic data: SVL 156 mm; TaL 24 mm; TL 180 mm; HL 7.1 mm; HW 4.7 mm; ED 1.0 mm; DSN 0.6 mm; DNE 1.5 mm; SnL 2.1 mm; RW 1.8 mm; RH 0.5 mm; DSR 17-17-17; SL 7/7; IL 7/7; PrO 1; PtO 2; SuO 1; IN 2; LoR 0; TMP 1 + 2 + 3; CS 2 + 2; V 171; SC 38.

Coloration of holotype in life ( Fig. 4A, B): The top of the head is boldly marked with a dense light yellowish cream colour from the rounded tip of the snout distally to the ends of the parietal shields, and laterally ending abruptly where the top of the head makes a sharp downturn to the vertical sides of the face. Dense black pigment surrounds the nostrils, completely colouring the small rostral, and makes two similar-sized black spots at the distal edges of the prefrontals. Small black specks are scattered loosely on the frontal and parietal scales and in some of the depressions between the head scales. The sides of the face are coal black beginning on the loreal and anterior-most labial in front of the eye and sweeping backwards from the orbit to become a two- to three-scale-wide dorsolateral intense black stripe all the way onto the tail. The eye is entirely embedded in the black lateral stripe. The iris is dark reddish orange or rust coloured. Also beginning on the upper labials are three or four light blue spots that fuse posteriorly and become a very distinct ventrolateral stripe including the ventral-most dorsal scale and a small lateralmost portion of the adjacent ventral scales, running in parallel with the wider black stripe all the way onto the sides of the tail. The ventral pattern is a shiny, slick black colour beginning at the base of the chin and running all the way to the tip of the tail. A bold white to very light blue midventral stripe about one-fifth the width of the black ventral scales begins on the second ventral scale and runs all the way to the anal scale. The undersurface of the chin is densely black, but the chinshields have small whitish blotches, and each lower labial has a bold white oval spot. The dorsal pattern consists of a thin, one-scale-wide, continuous, black line in the middle of an eight- or nine-scale light brown stripe. The main impressions of the colour pattern are a light brown snake with a boldly whitish head and a light bluish streak on dense black sides.

Coloration of the holotype in preservative ( Fig. 4C, 5): After 22 months in ethanol preservative, the overall coloration of the holotype appears only slightly faded from the condition of the live snake. The light brown dorsal colour has faded slightly, but the black-pigmented venter, lateral and middorsal stripes and chin are essentially the same. The blue colour of the lateral and midventral stripes has disappeared from the remaining underlying white colour.

Osteology ( Figs 6–13): Skull and postcranial skeleton are well ossified.

Snout: The premaxilla ( Fig. 8) is short and blunt. The ascending process is frontolaterally expanded and slanted posteriorly, giving it a wishbone shape from above, with its anterior surface having a sigmoid curvature in the lateral view. The transverse process is short and slightly curved, almost rectangular in shape in dorsal view. The posterior end of the vomerine process bears a notch; it fails to contact the tip of the septomaxilla. Both anterior and posterior sections of the nasal bone are tapered; the dorsal surface is bulged.

Braincase ( Fig. 7): The parietal is short and blunt, lacking a conspicuous lateral ridge (= adductor ridge). The lateral aspect of the prefrontal exhibits an expanded lateral lamina. The dorsal margin of the prefrontal bears a notch that almost contacts the lateral edge of the dorsal lamina of the nasal. The lateral aspect of the prefrontal shows a conspicuous outer orbital ridge. The lateral foot process is well developed, in contact with the dorsal surface of the maxilla, where it expands frontally and dorsally as a plate, giving it an inverted T-shape in lateral view. The medial extension is short, poorly differentiated and almost in contact with the pterygoid. The lacrimal foramen is large and vertically ovoid. The anterior margin of the frontal is trapezium-shaped; the lateral margin is slightly convex. The postorbital is highly reduced, crescent-shaped, not in contact with the frontal. Supraoccipital sagittal and adductor crests are poorly developed. The basisphenoid is wide, with no conspicuous lateral ridges on the ventral surface. The parasphenoid rostrum is not divided. The columella is short and thick, approximately as long as the diameter of its footplate.

Palatomaxillary arch: The maxilla ( Fig. 9) is short and stout, with a strong sigmoid curvature in dorsal and ventral view. The palatine process of the maxilla is elongate, with its tapered rounded tip strongly curved towards the ectopterygoid process. The ectopterygoid process is expanded, short and sharp. The maxilla has nine teeth on each side, with one row of replacement teeth on the lingual side. The palatine ( Fig. 10) bears five teeth, with one row of replacement teeth on the labial side. The choanal process of the palatine is curved towards the rostral end of the cranium and is shark-fin-shaped in dorsal view. The maxillary process of the palatine is short and small. The pterygoid ( Fig. 10) is slender and lanceolate, ~1.6 times the length of the palatine, bearing eight teeth on its anterior portion only (i.e. approximately half of its length), with one row of replacement teeth on the labial side. The ectopterygoid process is large and well defined, outwardly curved in dorsal view; its anterior part is horizontally expanded, bearing a large notch. The lateral furculum of the ectopterygoid is short and sharp; the medial furculum is straight and elongate with a pointed tip.

Suspensorium and mandible: The mandible ( Fig. 11) is stout and moderately curved. The dorsal process of the dentary is upwardly curved and expands further posteriorly than the ventral process. The dentary bone bears 12 teeth, with one row of replacement teeth on the lingual side. The largest dentary nutrient foramen is elongated, oval-shaped and lies below the seventh tooth. The prearticular crest of the compound bone is about twice as high as the surangular crest. The angular is slender and triangular. The splenial is triangular, tooth-shaped and slightly shorter than the angular. The supratemporal is flat and slender, having a sigmoid curvature in the dorsal view, with its posterior margin outwardly curved. The quadrate is expanded and stout, almost triangular in lateral view, and approximately as long as the supratemporal. The supratemporal angular surface of the quadrate is expanded and elongated. The stylohyal is long, completely fused with the quadrate, strongly protruding backwards.

Dentition: Diacranterian (presence of a diastema), aglyphous opisthodont (ungrooved fangs); prediastemal maxillary teeth: 7/7; postdiastemal maxillary teeth: 2/2; pterygoid teeth: 8/8; palatine teeth: 5/5; dentary teeth: 12/12.

Postcranial skeleton: Trunk vertebrae 175, neural spines smooth, ungrooved and not laterally expanded; conspicuous hypapophyses present on anterior trunk vertebrae only (approximately one-quarter of trunk vertebrae, hypapophyses abruptly decreasing in size from ~46th vertebra), absent on posterior vertebrae; caudal vertebrae 42, with distinct haemapophyses.

Distribution and natural history: The forest at the type locality is a fairly dense growth of small [10–13 cm diameter at breast height (DBH)] to medium (15–45 cm DBH) trees, with an occasional large tree> 45 cm DBH. Their trunks are densely grown, with a 5-cm-deep cover of moss to ≥ 1.5 m above the ground, but many trees are mossy to their canopy limbs. The trees are ~ 30 m high, and few have branches until ~ 25 m. Large aroids with big whorled leaves are epiphytes from ground level to the bottom of the canopy branches, but only on ~20% or less of the trees. An understorey layer of small-diameter brush with dwarf palms and long, strap-leaved Rapateaceae exists, with lots of pesky vines that make walking a challenge. The ground is covered with 30–45 cm of recently fallen leaf litter over peaty soil invaded by fine roots growing upwards from larger roots of the trees. Many of the small- to medium-sized trees are prop-rooted species, with a labyrinth of declivities among them filled with leaf litter and/or moss. These are havens for many tiny frogs that we hear calling all day long and at night. The mossy epiphyte load is not so vigorous as in a more substantial cloud forest, but getting there.

The skull of Paikwaophis kruki appears to be conducive to burrowing in the soft peaty soil immediately under the decomposing top layer of the leaf litter of cloud forests, and we assume that the new genus is fossorial or semi-fossorial, as also suggested by, inter alia, the highly reduced postorbital bones (Cundall and Irish 2008).

Paikwaophis kruki is saurophagous, at least in part, given that we found a few small lizard scales in the large intestine of the holotype.

Unlike its sister genus ( Xenopholis ), defensive mechanisms, such as body flattening and head hiding (e.g. Mira-Mendes et al. 2013, de Oliveira Meneses et al. 2022), have not been observed in Paikwaophis .