Avakubia avakubiensis ( Pilsbry, 1919 ) de Winter & Vastenhout, 2013

de Winter, A. J. & Vastenhout, N., 2013, Revision of the Afrotropical land snail genus Avakubia Pilsbry, 1919, with description of Pseudavakubia gen. n. and eleven new species (Gastropoda: Pulmonata: Streptaxidae), African Invertebrates 54 (2), pp. 605-663 : 624-628

Avakubia avakubiensis ( Pilsbry, 1919) , comb. n.

Figs 9A–J, 10E–H

Gulella (Avakubia) avakubiensis: Pilsbry 1919: 234 , fig. 102; Verdcourt 1962: 8; van Bruggen & Van Goethem 1997: 9, fig. 5; Schileyko 2000: 817, fig. 1069A; Wronski & Hausdorf 2010: 92; Rowson et al. 2011: 89, 91, 92.

not Gulella (Avakubia) avakubiensis of Degner 1934, nor of Ortiz de Zárate Lopez & Ortiz de Zárate Rocandio 1956.

Diagnosis: Shell differs from other Avakubia species by a combination of characters, like small size, subacute apex, and distant axial teleoconch ribs. Avakubia subacuminata generally has a larger, more elongate shell with a more sharply pointed apex and less convex protoconch whorls.

Description:

Shell ( Figs 9A–J, 10E–H, Table 1; characters of the holotype are taken from the available illustrations of this shell (see Remarks)): Small (mean H 3.3 mm), ovate-biconical, largest width at penultimate whorl. H:D 1.57–1.84 in available specimens, median 1.72, in holotype ca 1.62. Coiling tightness holotype unknown, 4.3–4.6 in available specimens, median 4.5. Whorls rather convex, including protoconch whorls.Apex subacute. Protoconch consisting of ca 2.0 whorls. Pilsbry’s (1919) description of the holotype protoconch sculpture broadly agrees with our observations. On last protoconch whorl, specimens from Kibale (Uganda), and Virunga National Park (DRC) have 14 irregularlyspaced spiral cords of strongly varying width, at most ca 9.5 µm wide but mainly (considerably) less. Spiral cords composed of rectangular particles of variable length, individually separated by a narrow cleft. Much finer lines are distinguishable between major spiral cords ( Fig. 10H). Teleoconch sculpture consists of distantly spaced, curved axial ribs, 7.2–9.4 ribs/mm on penultimate whorl, median 8.3, with fine spirals in interstices. Body whorl height generally less than half of shell height, BWH 45–53 % of H in available specimens, median 47 %, in holotype 49%. Peristome complete, mostly somewhat higher than wide, PH:PW 0.96–1.16 in available specimens, median 1.11, in holotype 1.05. PH 31–37% of H in available specimens, median 34%, in holotype 35%. PW 50–60% of D in available specimens, median 53%, in holotype 55 %. Apertural lip expanded and flaring, slightly reflected and not strongly incrassate. Two barriers visible in aperture: a weak, sometimes almost wanting, tooth-like thickening on mid-palatal wall and a projecting angular tooth that extends inwards as deeply entering lamella. Internal wall of body whorl with deep-set palatal fold, a short pale stripe is externally visible in translucent specimens. Presence of columella fold not discernible in aperture. Umbilicus narrow but open, widest in comparatively low-spired shells (e.g. Fig. 9J) .

Body colour: Not recorded.

Anatomy (a specimen from Uganda was dissected by B. Rowson, who kindly allowed us to study his unpublished drawings): Vas deferens enters penis subapically. Penis with distinct lateral diverticulum and short apical caecum, on which the penial retractor muscle is attached. Overall penial morphology similar to A. acuminata ( Fig. 6), but penis seems less elongate. Interior of penis with two strong and one minor pilasters, without any hooks or spines.

Holotype: DRC: Ituri , Avakubi, ca 1.318°N 27.544°E, J. Bequaert (shell could not be traced in AMNH, Christine Johnson, pers. comm., Dec. 2011). A photograph of the holotype shell in frontal view is available on http://research.amnh.org/iz/types_db/details.php?specimen_id=9951.

Other material examined: DRC: various sites within Virunga National Park [formerly Parc National d’Albert (PNA)] : 2 ad. dry shells, Abyalose, affl. Djuma , PNA, sta.A 511, 800 m, 12.vi.1953, G.F. de Witte ( RBINS) ; 2 ad., 1 juv. dry shells, Kabalwa, affl. dr. Talya , PNA, sta.A476, 1130 m, 21.v.1953, P. Vanschuytbroeck & J. Kekenbosch ( RBINS) ; 1 ad. dry shell, Tungula , PNA, sta.A1223, 16.xii.1959, H. Synave ( RBINS) ; 2 ad. in alcohol, Makano-Kisisile River , PNA, sta. B432, 1150 m, 27.v.1957, G.F.de Witte ( RBINS) ; 1 ad. dry shell, PNA, sta. A877, no further data ( RBINS) . UGANDA: 5 ad., 2 juv. dry shells, Bushenyi, Kasyoha-Kitumi Central Forest Reserve, Kamuzuku , ca. 0°15'S 30°09'E, 1250 m, 11–12.iv.2006, T. Wronski ( ZMH 52796 , 52819 , 53543 , 53478 ) ; 1 ad., 1 juv. dry shell, Kamwenge, Kibale Forest National Park, Fort Portal towards Ibanda at bridge crossing Dura River , 0°27'26"N 30°22'51"E, 1390 m, 13.iv.2006, T.Wronski ( ZMH 52709 ) ; 1 ad., 1 juv. dry shell, Kibale Forest National Park, Kanyanchu, Elephant wallow, 0°26'25"N 30°23'42"E, 1250m, 14.iv.2006, T. Wronski ( ZMH 52637 ) ; 1 dry shell, Kibale Forest National Park, Kanyanchu , 0°26'13"N 30°23'42"E, 1230 m, 14.iv.2006, T. Wronski ( ZMH 52744 ) ; 1 ad. dry shell, Masindi, Budongo Central, Forest Reserve: Masindi-Butiaba road between Karongo and Busingiro , 1°42'26"N 31°28'57"E, 1080 m, 17.iv.2006, T. Wronski ( ZMH 52425 ) ; 1 juv. dry shell, Mpigi, Mpanga Central Forest Reserve, Kafumo , 0°13'15"N 32°17'03"E, 1190 m, 24.iii.2006, T. Wronski ( ZMH 53293 ) ; 1 ad. dry shell, Bundibugyo District, Bwamba County, Semuliki National Park , ca 0.82°N 30.16°E, 720 m, 16.vii.1996, P. Tattersfield & J.A. Allen ( NMW.Z.1997.009) ; 1 ad. dry shell, 1 ad. in alcohol, Malabigambo Forest , ca 0°57'N 13°38'E, 1150 m, 4.ii.2007, P. Tattersfield & B. Rowson ( PT) .

Distribution ( Fig. 11): Specimens attributed here to A. avakubiensis originate from a large area extending from Avakubi in the eastern DRC to Kampala, Uganda, a linear distance of ca 500 km. This species has the easternmost distribution of the genus and by far the largest known range. Material from the north-western DRC (Bozene, Gemena) attributed by van Bruggen and Van Goethem (1997) to this species would, if correct, increase the range considerably. Unfortunately these specimens were not available. Material from central Gabon is attributed to A. avakubiensis with doubt (see Remarks).

Habitat: The species appears to have been collected in leaf litter on the forest floor in mid-altitude moist evergreen forest between 720 and 1390 m.

Remarks: Shells from the eastern DRC and Uganda agree rather well with the original description ( Pilsbry 1919) and available illustrations of the holotype of A. avakubiensis in (proportional) shell dimensions, rib distance, apical angle, and in whorl convexity.

We therefore confidently attribute these specimens to A. avakubiensis , although the holotype shell could not be studied. Still we stress the need to examine the holotype in order to confirm generic characters like an open umbilicus and the presence of a deepset palatal fold; the latter character may have been addressed by Pilsbry (1919) as “a low transverse fold … within the basal margin”, but this may also refer to what we here term the columellar lamella.

Material from two nearby localities in central Gabon (Reserve de la Lopé, Ogooué- Ivindo) is considered too poor (one worn adult and one juvenile shell plus two fragments) to confidently attribute this material to A. avakubiensis . In the PCA, the only adult shell was placed well within the A. avakubiensis cluster ( Fig. 2), indicating a strong resemblance in shell proportions. Fontaine et al. (2007) tentatively considered this a new species. In view of the large distance between the Gabonese records and the nearest locality of A. avakubiensis (nearly 1800 km), their view could well be correct. For the time being we classify these Gabonese specimens as A. cf. avakubiensis .