Avakubia semenguei 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 : 640-649
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|Avakubia semenguei de Winter & Vastenhout|
Figs 20, 21E–G
Gulella (Avakubia) n. sp.: de Winter & Gittenberger 1998: 240.
Etymology: The species is named after Eric-Joël Semengue, in recognition of the importance of his guiding and collection assistance in the field.
Diagnosis: A. semenguei is easily recognised from other Avakubia species by its large ovate shell (only the shell of A. acuminata is larger) with rapidly increasing whorls, flattened apex and very wide protoconch.
Shell ( Figs 20, 21E–G, Table 1): Large (mean H 4.9 mm), largest width at penultimate whorl. H:D 1.66–1.77, median 1.70, in holotype 1.66. Whorls expanding rapidly, coiling tightness 3.1–3.3, median 3.2, in holotype 3.2. Whorls moderately convex. Protoconch little elevated, consisting of ca 2.0–2.25 whorls. Apex comparatively flat. Protoconch sculpture consists of ca 11 distinct, comparatively conspicuous spiral cords, each 9–14 µm wide, consisting of poorly individualized, irregular-rectangular or quadrangular particles, on average 9 particles per 100 µm. In many spots the coarse spirals resemble wrinkled continuous cords, rather than series of beads. One or two spirals of intermediate coarseness, as well as very thin lines, occur occasionally between major cords. Teleoconch sculpture consists of obliquely curved axial ribs, with rather irregularly spaced spiral lines in interstices, 8.7–11.5 ribs/mm on penultimate whorl, median 10.5 ribs/mm, in holotype 11.5 ribs/mm. Last whorl proportionally large, BWH 51–54% of H, median 53 %, in holotype 53%. Peristome complete, higher than wide; PH : PW 1.08–1.29, median 1.16, in holotype 1.15. Peristome proportionally large: PH
36–40% of shell height, median 39 %, in holotype 40%. PW 54–59 % of shell width, median 57%, in holotype 58 %. Apertural lip expanded and flaring, slightly reflected, not strongly incrassate. Two barriers visible in aperture: a weak (or almost wanting) thickening on mid-palatal wall and not (or barely) projecting angular tooth that extends inwards as deeply entering lamella. Internal wall body whorl with comparatively long, deep-set palatal fold, externally visible in fresh specimens as a pale stripe ( Figs 20C, E). Columellar lamella not visible in aperture. Umbilicus rather narrow but open.
Body colour: Soft parts of live animal pale, without reddish pigment.
Holotype: CAMEROON: Sud Prov. : Minwo area, 6 km NE of Ebom, 15 km S of Lolodorf, plot I2 (de Winter & Gittenberger 1998), sta. CAM.055a, 3.10°N 10.73°E, 520 m, 21.iii.1996, A.J. de Winter & E.-J. Semengue, undisturbed high forest on hilly terrain ( RMNH.MOL.330191). GoogleMaps
Paratypes: CAMEROON: all from same square km as holotype, same collectors : 2 ad., 1 juv. dry shell, sta. CAM.022a, 470 m, 21.ix.1995 ( RMNH.MOL.42809) ; 1 ad. dry shell, sta. CAM.028a, 400 m, 27.ix.1995 ( RMNH.MOL.330192) ; 1 ad. dry shell, sta. CAM.039a, 470 m, 6.x.1995 ( RMNH.MOL.42810) ; 1 juv. dry shell, sta. CAM.065, 470 m, 2.iv.1996 ( RMNH.MOL.330193) ; 1 juv. in alcohol, sta. CAM.070a, 590 m, 2.iv.1996 ( RMNH.MOL.330194) ; 1 juv. dry shell, sta. CAM.076a, 480 m, 9.iv.1996 ( RMNH.MOL.330195) ; 4 juv. in alcohol, sta. CAM.082a, 470 m, 12.iv.1996 ( RMNH.MOL.330196) .
Distribution ( Fig. 25): Only known from a single square km in Southwest Cameroon, 90 km east of Kribi. The collecting technique of beating the vegetation over an umbrella was used extensively in other areas in Southwest Cameroon, but yielded only other Avakubia species. The species might be a narrow range endemic.
Habitat: Collected from understorey vegetation up to 3 m above the forest floor in relatively undisturbed rainforest between 400 and 500 m. The species lives syntopically with A. acuminata and A. fruticicola , which are also arboreal.
Avakubia subacuminata de Winter & Vastenhout , sp. n. Figs 5G, 22–24
Etymology: Refers to the superficial resemblance to the larger and more strongly acuminate A. acuminata .
Diagnosis: Superficially resembles A. acuminata by the acuminate apex and tapering spire, but has a much smaller, shorter-spired shell with tighter coiled whorls and a less sharp apical angle. The shell of A. avakubiensis is generally smaller with less tightly coiled whorls, proportionally larger body whorl, more convex protoconch whorls, and less acute apex. It is easily distinguished from other Avakubia species by the acuminate apex, proportionally small body whorl and slowly increasing whorls, among other characters.
Shell ( Figs 22, 23, Table 1): Small to medium-sized (mean H 3.8 mm), ovate-biconical, largest width at penultimate whorl, occasionally preceding whorl equally wide. H:D 1.65–1.93, median 1.75, in holotype 1.76. Whorls expanding rather slowly, coiling tightness 4.5–5.0, median 4.8, in holotype 4.8. Whorls moderately convex. Apex acuminate. Protoconch with ca 2.0–2 ¼ whorls. Protoconch of specimens from the Ebimimbang area with 10–11 major spiral cords on second whorl, each at most 6.5 µm wide, usually somewhat less, made up of rectangular particles of rather unequal size (each ca 5–17µm long, on average 9 particles per 100 µm), which become individually less distinct towards teleoconch. Major cords irregularly interspaced by thinner, seemingly solid, lines. Material from the Nyangong area has a larger number of somewhat wider (up to 8 µm) major cords (12–15) on second whorl; distinction between major and minor cords much less clear than in the Ebimimbang material, and individual particles appear to be shorter, but they are individually less clearly recognisable than in the Ebimimbang material. Teleoconch with sculpture of slightly oblique, regularly spaced axial ribs, ca 6.6–9.4 ribs/mm on penultimate whorl, median 7.6 ribs/mm, in holotype 6.9 ribs/mm, interstices with fine, comparatively regularly spaced spiral lines. Last whorl proportionally small, BWH 38–45 % H, median 41%, in holotype 42 %. Peristome entire, proportionally small, generally slightly higher than wide; PH:PW 0.97–1.15, median 1.07, in holotype 1.09. PH 29–32 % of H, median 31 %, in holotype 32 %. PW 48–56% of D, median 51%, in holotype 51 %. Apertural lip expanded and flaring, slightly reflected, not strongly incrassate. Two barriers visible in aperture: a weak or almost wanting, tooth-like thickening on mid-palatal wall and a projecting angular tooth that extends inwards as deeply entering lamella. Wall of body whorl with deep-set palatal fold ( Fig. 5G), externally visible in fresh specimens as a pale stripe ( Figs 22C, E). Columellar lamella rather small ( Fig. 5G), not visible externally. Umbilicus narrow, slightly more open than in most other Avakubia species.
Body colour: Live animal with orange-reddish soft parts.
Anatomy ( Fig. 24; one specimen dissected): Atrium about as wide as long, thin-walled. Penis subcylindrical, elongate, with short apical caecum as well as lateral diverticulum that is longer than wide. Vas deferens convolute along female genital tract, becoming more straight, wider and muscular upon reaching penis; it enters penis subapically cutting off a short caecum. Penis retractor muscle convolute, originating from columella muscle and inserting on penial apex, extending under terminal portion of vas deferens. Interior of distal penis without obvious pilasters but with irregularly-shaped tissue pads. Vagina short but distinct. Bursa copulatrix with ca 2.5 mm long narrow duct and elongate terminal sac close to albumen gland. Free oviduct short. Hermaphrodite duct with long, tube-like, convolute talon. No chitinous spines found inside penis.
Paratypes: CAMEROON: Sud Prov. : all within 5 km from Ebimimbang-Saa, S of the Bikoui River (= R. Lokoundjé), same collectors as holotype : 1 ad. dry shell Ebimimbang , ca 2 km WSW of Saa, sta. CAM.042, 3.038°N 10.456°E, 120 m, 10.x.1995, swamp forest ( RMNH.MOL.330198) GoogleMaps ; 1 ad. dry shell, Ebimimbang , 1 km SW of Saa, sta. CAM.043, 3.041°N 10.457°E, 110 m, 11.x.1995, high forest on flat terrain ( RMNH. MOL.330199) GoogleMaps ; 2 ad. dry shells, 1 ad. in alcohol Ebimimbang , sta. CAM.051, 3.038°N 10.477°E, 120 m, 12–18.x.1995, 25-year-old cocoa plantation with scattered large forest trees ( RMNH.MOL.330200–330201) GoogleMaps ; 1 ad., dissected soft parts in alcohol, Ebimimbang , 1 km S of Saa, secondary forest on an abandoned field along River Bikoui (= R. Lokoundjé), sta. CAM.052, 3.042°N 10.467°E, 110 m, 19.x.1995, floor litter ( RMNH.MOL.330202) GoogleMaps ; 1 ad. dry shell, sta. CAM.052, 23.v.1996 ( RMNH.MOL.330203) ; 1 juv. dry shell, Ebimimbang , 4 km WSW of Saa, high forest, sta. CAM.117, 3.050°N 10.433°E, 150 m, 25.v.1996 ( RMNH.MOL.330204) GoogleMaps ; 2 ad. dry shells, Ebimimbang , 4 km W of Saa, swamp forest, sta. CAM.120, 3.050°N 10.433°E, 120 m, 27.v.1996 ( RMNH.MOL.330205) GoogleMaps ; 1 ad. in alcohol, Ebimimbang , 4 km W of Saa, swamp forest, sta. CAM.129, 3.050°N 10.433°E, 120 m, 29.v.1996 ( RMNH.MOL.330206) GoogleMaps ; 1 ad. dry shell Ebimimbang , 3 km WSW of Saa, young secondary forest, sta. CAM.133, 3.046°N 10.435°E, 110 m, 30.v.1996 ( RMNH.MOL.330207) GoogleMaps .
Other material examined: CAMEROON: Sud Prov. : 1 juv. dry shell, Nyangong, 30 km S of Lolodorf, undisturbed rainforest, sta. CAM.100, 2.943°N 10.736°E, 700 m, 7.v.1996 ( RMNH.MOL.330208); 1 ad., 4 juv. dry shells, Meka’a II, W of Nyangong, undisturbed rainforest, sta. CAM.106, 107, 110, 111, 2.967°N 10.733°E, 690–1000 m, 17–18.v.1996 ( RMNH.MOL.330209–330212) GoogleMaps .
Distribution ( Fig. 25): Known from two areas in Southwest Cameroon, which are some 35 km apart and differ substantially in altitude (100–150 m in Ebimimbang vs 690– 1000 m in Nyangong).
Habitat: Collected from leaflitter on the forest floor, except for a single specimen in a vegetation beating sample. The species was taken at ca 100–150 m in a variety of habitats: little disturbed high forest, more or less undisturbed swamp forest, a 25-year-old cocoa plantation with some remaining forest trees as well as in young secondary forest.A few specimens were collected in floor litter in undisturbed forest at 690–1000 m altitude (see below). In the Ebimimbang area A. subacuminata appears to be the only Avakubia species present (but see Remarks); in the Nyangong area it occurs sympatrically with A. fruticicola , which inhabits the understorey vegetation, however.
the animal is differently coloured (reddish orange instead of colourless/whitish), the genital anatomy differs in various details, and the species has ground-dwelling rather than arboreal habits. A. subacuminata does not seem to occur in an intensively sampled square km of forest in between both localities at an intermediate altitude (400–500 m), where three other Avakubia species were observed. The attribution of the Nyangong material to A. subacuminata is somewhat doubtful, because of small differences in protoconch sculpture details. The only adult shell from the Nyangong area could not be separated from the lowland specimens by shell proportions, however. Confirmation of the tentative identification requires collection of fresh material for anatomical and molecular studies.
Two juvenile shells with Avakubia -like sculpture were collected in leaf-litter in the Ebimimbang area. The protoconchs are very small and possess a more acuminate apex than any of the recognised Avakubia species, as well as distinctive coarse spiral sculpture ( Figs 23E, F). These potentially represent still another unknown Avakubia species, but adult shells are necessary to confirm the tentative generic attribution.
Genus Pseudavakubia de Winter & Vastenhout , gen. n.
Etymology: The name refers to the strong resemblance of the shells to those of the genus Avakubia . Gender feminine.
Type species: P. majus de Winter & Vastenhout , sp. n.
Description: Shell small, H 2.9–4.3 mm, elongate ovate or cylindrical, penultimate whorl always wider than body whorl, with 6–7¼ whorls that generally expand slower than in Avakubia species, hence coiling tightness is higher (4.9–5.8). Last whorl proportionally smaller than in most Avakubia species, taking up 38–44% of H. Peristome proportionally small, PH 29–35% of H, PW 50–57 % of D.Aperture in most species ( P. liberiana excepted) with a conspicuous, pointed palatal tooth, and a protruding angular tooth that continues as a deeply inrunning angular lamella. Palatal fold and columellar lamella absent. Umbilicus closed, umbilical depression with radiating ribs. Protoconch with ca 2¼ whorls not regularly increasing in width, but appearing more or less laterally compressed. Protoconch consists of two distinct portions: the first ca 1½ whorls appear rather smooth and shining at lower magnification, but at high magnification fine spiral sculpture can be distinguished ( Fig. 29B); the sculpture changes abruptly to sharp, distant spiral cords on the last ca ¾ whorl. These spiral cords are solid, not composed of series of particles as in Avakubia ( Fig. 29C). Teleoconch sculpture consists of sharp, regular ribs, with fine spiral lines in the interstices.
Anatomy ( Fig. 27; based on a single dissection of P. majus ): Penis twice as long as wide, muscular, robust, with a strong retractor muscle inserting subapically, next to the entrance site of the vas deferens, cutting off a short, spherical apical caecum. Vas deferens proximally rather straight, becoming convolute between the vagina and penial apex; the terminal portion somewhat rounded, swollen and muscular, narrowing just before entering the penis. Penis internally with two bulky, longitudinal pilasters. No chitinous spines were found inside the penis. Vagina short but distinct, rather wide close to the penis. Free oviduct abruptly widening into a pouch-like uterus containing a single, shelled embryo. Duct of bursa copulatrix rather long, distally widest, tapering towards the small bursal sac, which is situated close to the albumen gland. Talon a long, stiff, exposed, tube at the base of the (remains of) the albumen gland. Spermoviduct with large, elongate acini. Radula typical carnivorous; a complete row no could be studied; individual lateral/marginal teeth elongate, curved and sharply pointed, similar in shape to those in A. acuminata .
Distribution: Ghana, Liberia.
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