Atheris hetfieldi Ceríaco & Marques & Bauer 2020, sp. nov.

Atheris hetfieldi sp. nov.

Zoobank — Atheris hetfieldi: lsid: http://zoobank.org:act: 86771446-1888-4FC6-9C6B-9D29D6FA4956

Atheris squamigera squamigera [part]: Capocaccia (1961: 304)

Atheris chlorechis: Mertens (1964: 235)

Capocaccia (1961) reported on a specimen from Moka collected by Leonardo Fea that was not conspecific with the remaining A. squamigera from the same collection. According to the author, the specimen posed some difficulties in its identification, in that it had “intermediate characters” of both A. squamigera and A. chlorechis. The specimen (MSNG/CE 30428a) has 153 ventral scales, 50 subcaudals, 29 scales rows around the neck, 25 at midbody, and 19 before the cloaca, 10 right supralabials, nine left, 11 right infralabials, 10 left, three scales between the nasals and eye on the right side of the head, two on the left, 12 interoculars, 14 oculars on the right side, 15 on the left side, and only one row of scales between the eye and supralabials. Capocaccia (1961) considered this specimen odd because although the counts of ventrals, subcaudals, dorsal scale rows, supra- and infralabials fall within the range of variation of both A. squamigera and A. chlorechis, the number of interoculars (12), is greater than the known number for A. squamigera (seven to nine), fitting the range of A. chlorechis (nine to 13), but the number of oculars was, according to Capocaccia (1961), more typical of A. squamigera (10 to 17) than A. chlorechis (15 to 18). The author opted to not allocate the specimen to any specific taxon, keeping it in the same account as the remaining Bioko Atheris squamigera. Mertens (1964) referred to this specimen as A. chlorechis, noting that he had not in his possession any specimen that would be referable to it. Specimen CAS 207870 agrees entirely with the specimen referred by Capocaccia (1961) and represents the second known record of the taxon.

Holotype. CAS 207870 (field number RCD-13410, Fig. 3), an adult female from Moka road (3.38844º, 8.65878º, 1296 m), Bioko Island, Equatorial Guinea, collected by Jens V. Vindum and Lindsay G. Henwood on 11 of October 1998.

Paratype. MSNG / CE 30428 a, an adult female from Moka (3.35081º, 8.66254º, 1369 m), Bioko Island, Equatorial Guinea, collected by Leonardo Fea in 1901–1902.

Diagnosis. The newly described species can be distinguished from all other members of the genus by a combination of characters: 1) “horns” above the eyes absent; 2) one or two rows of scales between the eyes and supralabials; 3) lack of lanceolate or acuminate scales on top of the head; 4) lack of conspicuous lateral and/or dorsal markings on the head; 5) 23 to 25 dorsal scale rows at midbody; 6) 153 ventral scales; 7) 47 to 50 undivided subcaudals; 8) four suprarostrals; 9) 10 interorbitals and 19–20 interrictals; 10) a background dorsal coloration brownish-green, with a series of large transverse dark markings.

Specifically, regarding the more geographically proximate species of the genus, the newly described species can be easily distinguished from the sympatric A. squamigera by having four suprarostrals (usually three in A. squamigera, see Fig. 4), three scales between the eye and the nasal (two in A. squamigera), and an higher number of interrictals (19–20 in Atheris hetfieldi sp. nov. versus 14 to 16 in A. squamigera); it can be distinguished from the phenetically similar West African Atheris chlorechis by having 23 to 25 midbody scale rows (25–37 in A. chlorechis), a brownish-green coloration pattern with dark brown marking on the dorsum (uniformly leaf green in A. chlorechis), and four suprarostrals of different sizes (the outer two much larger that the inner two in A. hetfieldi sp. nov. versus four irregular but small and about the same size in A. chlorechis), and a smaller number of interrictals (19–20 in A. hetfieldi sp. nov. versus 25–27 in A. chlorechis). It can be immediately distinguished from A. subocularis by having one or two rows of scales between eye and supralabials (eye in direct contact with supralabials in A. subocularis). It differs from A. mongoensis in having 23 to 25 midbody scales rows (19–21 in A. mongoensis), a higher number of ventral scales (153 in A. hetfieldi sp. nov. versus 141–152 in A. mongoensis), and in having undivided subcaudals (divided in the posterior part of the tail in A. mongoensis). It can be distinguished from A. broadleyi by lacking a conspicuous dark band between the posterior part of the eye and the corner of the mouth (usually present in A. broadleyi), by having one or two rows of scales between eye and supralabials (suboculars always in direct contact with supralabials in A. broadleyi), by having four suprarostrals (only three in A. broadleyi); a higher number of interoculars (10–12 in A. hetfieldi sp. nov. versus 3–8 in A. broadleyi), and a higher number of interrictals (19–20 in A. hetfieldi sp. nov. versus 14–18 in A. broadleyi). The new species differs from A. anisolepis by having a higher number of interorbitals (10–12 in A. hetfieldi sp. nov, versus 6–8 in A. anisolepis), a higher number of interrictals (19–20 in A. hetfieldi sp. nov. versus 14 –18 in A. anisolepis), and by having four suprarostrals (usually three in A. anisolepis). Finally, it can be easily distinguished from A. hirsuta by lacking lanceolate or acuminate scales on top of the head (a distinctive “hairy” appearance in A. hirsuta) by having three scales between the eye and the nasal (two in A. hirsuta), and by having 23–25 midbody scale rows (16 in A. hirsuta).

Besides the obvious geographic distribution gap, the newly described species can be distinguished from their central and eastern African congeners by the following characters: it can be immediately distinguished from A. ceratophora and A. matildae by the lack of supraocular scales similar to “horns”; it can be distinguished from A. hispida and H. acuminata by lacking lanceolate or acuminate scales on top of the head (a distinctive “hairy” appearance in A. hispida and A. acuminata); it can be distinguished from A. desaixi by not having lateral scales serrated, having 20 interrictals (22 in A. desaixi), a lower number of ventrals (153 in A. hetfieldi sp. nov. versus 164 –168 in A. desaixi), and by having a dark-green background dorsal coloration (black in A. desaixi); from A. nitschei by lacking black arrowhead markings on the top of the head and black lateral stripe from the tip of snout, through the eye to the temporal region (typical of A. nitschei); from A. rungweensis by having a lower number of interrictals (20 in A. hetfieldi sp. nov. versus 24–26 in A. rungweensis), by having four suprarostrals (usually three in A. rungweensis) and by lacking the typical yellow dorsolateral zig-zag lines and yellowish markings on the labials; from A. katangensis by having a higher number of ventrals (153 versus 133–144 in A. katangensis) and lacking serrations on the lateral scales (serrated in A. katangensis); from A. barbouri by having a prehensile tail (non-prehensile tail in A. barbouri; see Spawls & Branch 2020), a higher number of ventrals (153 in A. hetfieldi sp. nov. versus 115–127 in A. barbouri), a higher number of subcaudals (47–50 in A. hetfieldi sp. nov. versus 15–23 in A. barbouri), a considerably greater maximum known total length (52 cm in A. hetfieldi sp. nov. versus 36.9 cm in A. barbouri); and from A. mabuensis by its greater maximum known total length (52 cm in A. hetfieldi sp. nov. versus 38.4 cm in A. mabuensis), by having one or two rows of scales between eye and supralabials (suboculars in direct contact with supralabials in A. mabuensis), and a higher number of ventrals (153 in A. hetfieldi sp. nov. versus 128–137 in A. mabuensis).

Description of holotype. An adult female (Fig. 3), 44 cm SVL, body relatively slender anteriorly, but relatively robust in the mid and posterior parts; subtriangular in cross-section. Tail 8 cm (SVL/TL 5.5), thin and most likely prehensile. Head triangular, with a very distinct neck, bluntly rounded snout and swollen supraorbital region that does not bear elongate scales; eye relatively large, laterally placed, and with a horizontal diameter slightly smaller than distance between eye and snout.

Crown of the head covered in small scales, that are larger in the temporal region and smaller between the eyes; they bear a prominent keel that is extended into a small and feebly rounded, brownish knob; the rostral is flattened, rectangular, about four times broader than high, contacting first supralabial and four large, unkeeled suprarostrals, of which the two in the middle are the smallest and about 1.5 times higher than wide, exterior suprarostrals pentagonal, about two times higher than wide, nasal wider than high, with raised posterior edge; nostril oval and approximately in the center of the nasal; internasals five, all feebly keeled; interrictals 20; interorbitals 10, keeled, central scales smaller than those in the outer sides; circumoculars 15/18, blunt, not keeled; one row of suboculars present, separating the circumoculars from the supralabials; circumoculars separated from nasal by two rows of irregular, unkeeled scales; supralabials 10/10, fifth largest; infralabials 11/11, posterior-most feebly keeled, and first in contact at the midline behind the mental, and separating the latter from six pairs of chin shields, the first largest; mental triangular, approximately as wide as deep; gulars bordering chin shields feebly keeled, but prominently-keeled towards the rictus; four preventrals, fourth largest; 153 ventrals; 47 undivided subcaudals (excluding terminal spine); anal entire; dorsal scales about 2.5 times as long as wide, becoming shorter posteriorly; 21 rows anteriorly; 23 rows at midbody, 17 rows posteriorly; keel on dorsal scales increasing in height from base, not terminating in a knob; paraventrals larger than other dorsals, with a feeble keel.

Background dorsal coloration brownish-green, with a series of large transverse dark markings, starting on the neck region and extending to the tail base. Tip of the tail black. Ventral coloration dirty green, becoming darker towards the tail region.

Variation. Variation in measurements and scalation of the paratypes of A. hetfieldi sp. nov. is presented in Table 1. The paratype agrees in general with the holotype, although it has only one row of scales between the eye and the supralabials (two in the holotype) and a higher number of neck, midbody and caudal scale rows, and interoculars (see Table 1).

Distribution. Known only from the vicinity of Moka, on Bioko Island, Gulf of Guinea (Fig. 2).

Habitat and natural history notes. Almost nothing is known regarding the habitat and natural history of the newly described species. The Moka area is dominated by equatorial rain forest at the base of the island’s extinct volcano. The species, like all other Atheris species (with the exception of A. barbouri), is arboreal.

Etymology. The species is named after James A. Hetfield (1963–present), lead vocalist and guitarist of the heavy metal band Metallica, for the inspiration, endurance and sanity that his music provides to the authors while roaming the academic world. The name is here applied as a genitive masculine. We propose the English common name of Hetfield’s Bush Viper.