Letheobia akagerae, Dehling & Hinkel & Ensikat & Babilon & Fischer, 2018

Dehling, J. Maximilian, Hinkel, Harald H., Ensikat, Hans-Jürgen, Babilon, Kenny & Fischer, Eberhard, 2018, A new blind snake of the genus Letheobia (Serpentes: Typhlopidae) from Rwanda with redescriptions of L. gracilis (Sternfeld, 1910) and L. graueri (Sternfeld, 1912) and the introduction of a non-invasive preparation procedure for scanning electron microscopy in zoology, Zootaxa 4378 (4), pp. 480-490 : 482-487

Letheobia akagerae sp. nov.

Akagera Gracile Blind Snake ( Figs. 1–5 )

Holotype: ZFMK 100862, adult; Rwanda, Akagera National Park , Ruzizi Tented Lodge (1°54'24.90"S, 30°42'58.42"E; approx. 1290 m), collected on 8 July 2012 by construction workers, preserved by Kenny Babilon.

Diagnosis. The new species is assignable to the genus Letheobia for showing the following characters that in combination are diagnostic (Pyron & Wallach, 2014): Dorsal and lateral head profiles rounded; rostral broad; T-0; lateral snout profile rounded; body form gracile; eye invisible; coloration pink (pigmentless); body with 22 longitudinal scale rows without reduction; tail short with 13 subcaudals and apical spine; inferior nasal suture in contact with first supralabial; preocular in contact with second and third supralabials; subocular present. It extends the known total length/midbody width ratio in the genus (42–129; Pyron & Wallach, 2014) to 131 and the known maximum number of middorsal scale rows for any species in the genus (311–737; Broadley & Wallach, 2007; Pyron & Wallach, 2014) to 834.

Description of the holotype. Total length 457.5 mm; midbody diameter 3.5 mm; body extremely slender, total length/midbody diameter ratio 130.7 ( Figs. 4 , 5 ); longitudinal scale rows 22-22-22; 834 middorsal scale rows; 13 subcaudals; tail short (length 5.8 mm), 1.3 % of total length, ending in short apical spine; snout rounded in dorsal profile, in lateral profile bluntly rounded with angular horizontal edge ventrally ( Fig. 2 ); rostral broad (2.0 mm), two-thirds head width (3.1 mm), rounded posteriorly, ventrally broad with almost parallel sides; frontal broad and long, crescentic, bordering nasals, two-thirds width of rostral ( Fig. 1 ); supraocular rhomboid, oblique, about as broad as frontal, its lateral apex wedged between nasal and ocular; ocular half size of supraocular and one-fifth size of preocular, almost in contact with subocular but separated by one temporal, its ventrolateral apex between preocular and temporal; temporal about as large as ocular; subocular about twice size of temporal and ocular; posterior edges of rostral, nasal, preocular and subocular forming continuous line ( Fig. 2 ); eyes invisible; nasal divided; inferior suture bowed laterally, arising from first supralabial at border with second supralabial; nostril semicircular with rounded lateral edge, orientated ventrally; supralabials numbering four on each side; preocular in contact with second and third supralabial; second supralabial about twice size of first supralabial and about equal in size to third supralabial; fourth supralabial about 1.5 times size of second or third supralabial; supralabial imbrication pattern T-0 (no supralabial overlaps superior head shields); rostral, anterior two-thirds of nasal, and anterior halves of preocular and subocular more or less regularly scattered with tiny, rounded pits ( Figs. 1–3 ).

Colouration. In life, overall brightly pink with darker reddish pattern where body scales overlap ( Fig. 4 ). Head lighter, pinkish white. In preservation uniformly beige ( Fig. 5 ).

Comparison. Letheobia akagerae can be distinguished from all congeners by its unique middorsal scale count (834), which exceeds the known range for this character in the genus (311–737; Broadley & Wallach 2007; Pyron & Wallach 2014) considerably, and the extreme slenderness of its body with a total length/midbody width ratio of 130.7 ( Fig. 5 ), which is outside the previously known range for the genus (42–129; Pyron & Wallach 2014). The non-reducing number of longitudinal scale rows (22) further separates the new species from L. acutirostrata (Andersson, 1916) , L. graueri , L. jubana Broadley & Wallach, 2007 , L. kibarae (de Witte, 1953) , L. newtoni (Bocage, 1890) , L. pembana Broadley & Wallach, 2007 , L. praeocularis (Stejneger, 1894) , L. somalica (Boulenger, 1895) , L. stejnegeri (Loveridge, 1931) , and L. sudanensis (Schmidt, 1923) , all of which have at least 24 scale rows, and from L. debilis (Joger, 1990) , L. episcopus (Franzen & Wallach, 2002) , L. erythraea (Scortecci, 1928) , L. lumbriciformis (Peters, 1874) , L. mbeerensis Malonza, Bauer & Ngwava, 2016 , L. rufescens (Chabanaud, 1916) , and L. wittei (Roux-Estève, 1974) , all of which have 21 or less scale rows (Pyron & Wallach 2014; Malonza et al. 2016). The total length of 457.5 mm exceeds the known maximum length for L. acutirostrata (447), L. caeca (Duméril, 1856) (443), L. crossii (Boulenger, 1893) (310), L. episcopus (318), L. erythraea (245), L. feae (Boulenger, 1906) (330), L. graueri (450), L. largeni Broadley & Wallach, 2007 (274), L. leucosticta (Boulenger, 1898) (230), L. lumbriciformis (445), L. mbeerensis (280), L. newtoni (400), L. pallida Cope, 1868 (192), L. pauwelsi Wallach, 2005 (310), L. pembana (158), L. praeocularis (438), L. simoni (Boettger, 1879) (239), L. swahilica Broadley & Wallach, 2007 (191), L. toritensis Broadley & Wallach, 2007 (268), L. uluguruensis (Barbour & Loveridge, 1928) (245), and L. wittei (310) (Pyron & Wallach 2014; Malonza et al. 2016). The rounded snout with a distinct angular horizontal edge of L. akagerae distinguishes the species from L. largeni , L. pallida , L. pembana , L. swahilica , L. toritensis , and L. uluguruensis , all of which have a prominent rounded snout without a horizontal edge, and from L. acutirostris and L. erythraea , which have a pointed snout ( Broadley & Wallach 2007).

The new species is superficially most similar to L. graueri and especially L. gracilis . Besides the aforementioned characters (elongation ratio and middorsal scale count) it differs from both species by having a posteriorly rounded rostral (vs. truncated in L. graueri and L. gracilis ); the sides of the ventral part of rostral running almost parallel (vs. rostral continuously tapering from nostril in near-straight lines on both sides); the ocular being half the size of the supraocular (vs. about as large as supraocular); the ocular almost contacting the subocular (vs. ocular widely separated from subocular by temporal); posterior edges of rostral, nasal, preocular and subocular forming continuous line (vs. posterior edges of these scales not forming continuous line). Besides the aforementioned differences in maximum total length and number of longitudinal scale rows, the new species further differs from L. graueri in the second supralabial being about twice the size of the first supralabial (vs. second supralabial as large as first) and the fourth supralabial being larger than the third by a factor of 1.5 (vs. being smaller by the same factor). Letheobia akagerae further differs from L. gracilis in having a crescentic frontal (vs. frontal trapezoid), bordering the nasals (vs. separated from nasals by supraoculars) and being two-thirds width of rostral (vs. half width of rostral); inferior nasal suture arising from first supralabial (vs. arising from second supralabial) and four-fifths of ventral edge of preocular being bordered by second supralabial, one-fifth by supralabial (vs. about half of edge being bordered by second and third supralabial, respectively).

Etymology. The specific epithet refers to the type locality, the Akagera National Park in eastern Rwanda.

Distribution, habitat and conservation status. The holotype of Letheobia akagerae was found when soil was dug during construction work. The type locality is in gallery forest near the shores of Lake Ihema at around 1290 m a.s.l. Three additional specimens were observed and photographed in tree savanna on a nearby hilltop in the headquarters area of the national park (1°52'29.56"S, 30°42'55.49"E; 1°52'37.32"S, 30°42'50.42"E; 01°52'39.05"S, 30°42'52.80"E; approx. 1600m a.s.l.) slithering on the ground after heavy rainfalls during the day. All of them showed the extreme elongation of the body and a pinkish live colouration but unfortunately none were retained for further examination. The species may be more widespread and even occur in cultivated areas outside the national park. Until further data on the distribution and abundance of the species becomes available, we recommend L. akagerae be classified as Data Deficient according to the IUCN Red List Criteria ( IUCN 2017).

Figures

FIGURE 1. SEM images of head scalation of the holotype of Letheobia gracilis (ZMB 22030; left), the holotype of L. akagerae sp. nov. (ZFMK 100862, centre), and a specimen of L. graueri (ZFMK 63138, right), showing the dorsal side (top row) and the ventral side (bottom row).

FIGURE2. SEM imagesof lateral view of the head of theholotype of Letheobia gracilis (ZMB 22030;top), the holotypeof L. akagerae sp. nov. (ZFMK 100862, centre), and a specimen of L.graueri (ZFMK 63138, bottom).

FIGURE 3. SEM images showing details of the scale pits in (A) the holotype of Letheobia graueri (ZMB 27161) and (B) the holotype of L. gracilis (ZMB 22030).

FIGURE 4. Holotype of Letheobia akagerae sp. nov. (ZFMK 100862) in life.

FIGURE 5. Preserved holotypes of Letheobia gracilis (ZMB 22030, total length 465.4 mm; outside) and L. akagerae sp. nov. (ZFMK 100862, total length 457.5 mm; centre); showing the extreme elongation in the new species.