Avakubia fruticicola 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 : 632-635

Avakubia fruticicola de Winter & Vastenhout , sp. n.

Figs 5H, 14, 15, 18A–D

Gulella (Avakubia) cf. avakubiensis: de Winter & Gittenberger 1998: 239 .

Etymology: From Latin frutex (shrub, bush) and colere (to inhabit), in reference to the understorey-dwelling habit of this species.

Diagnosis: Avakubia fruticicola differs from other Avakubia species by the combination of its small sized shell with proportionally large body whorl, rounded apex, and close-set teleoconch ribs.

Description:

Shell ( Figs 14, 18A–D, Table 1): Small (mean H 3.3 mm), ovate-biconical, largest width at penultimate whorl. H:D 1.62–1.79, median 1.68, in holotype 1.67. Whorls expanding comparatively fast, coiling tightness 4.0–4.4, median 4.2, in holotype 4.2. Whorls convex. Apex raised, but more flattened than most similarly­sized species. Protoconch consisting of ca 2 whorls. Protoconch sculpture (on second whorl) composed of ca 13 spiral cords, more or less regularly spaced, each 3.5–7.6 µm wide, without thinner lines between them. Spirals cords are made up of series of adjoining, but distinct, particles of variable length. Teleoconch sculpture with comparatively close-set, regularly spaced, curved axial ribs, 10.7–12.8 ribs/mm on penultimate whorl, median 11.3, in holotype 11.5, interstices with fine spiral lines. Body whorl proportionally large, BWH 49–55% of shell height, median 53%, in holotype 53%. Peristome complete, roundish to (mostly) somewhat higher than wide; PH:PW 0.92–1.15, median 1.11, in holotype 1.10. PH 35– 39% of H, median 37%, in holotype 37%. PW 53–61% of D, median 57%, in holotype 56%. Apertural lip expanded and flaring, slightly reflected, not strongly incrassate. Two barriers visible in aperture: a rather weak, often nearly absent, 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, externally visible as pale stripe in fresh specimens ( Figs 18C, D). Columellar lamella not visible in aperture, facing palatal fold, little pronounced ( Fig. 5H). Umbilicus punctiform but open.

Body colour: Live animal reddish, dried-in tissue often retains red pigments.

Anatomy ( Fig. 15; one paratype dissected): Genitalia overall similar to those in A. acuminata and A. subacuminata , but smaller. Upper penis appreciably narrower and more muscular than distal portion. Lateral diverticulum of penis, if present, rather poorly developed, merely an inconspicuous dilatation at the transition of two penial portions. Internal penis not examined.

Radula: No complete row could be studied, but individual lateral/marginal teeth similar in shape to those in A. acuminata .

Holotype: CAMEROON: Sud Prov. : 14 km S Lolodorf, plot I2 (de Winter & Gittenberger 1998, sta. CAM.22a), 3.10°N 10.73°E, 470 m, 21.ix.1995, A.J. de Winter & E.J. Semenguei ( RMNH.MOL.42806) . Paratypes: CAMEROON: same locality and collectors as for holotype but 460–530 m: 1 juv. dry shell, 1 ad. in alcohol, sta. CAM.010, 30.viii.1995 ( RMNH.MOL.42802, RMNH.MOL.254634); 1 ad. dry shell, sta. CAM.011a, 30.viii.1995 ( RMNH.MOL.42803); 1 juv. dry shell, sta. CAM.012a, 31.viii.1995 ( RMNH. MOL.42804); 2 ad. dry shells, sta. CAM.018a, 19.ix.1995 ( RMNH.MOL.42805); 3 ad. dry shells, sta. CAM.038, 6.x.1995 ( RMNH.MOL.42807); 1 ad. dry shell, sta. CAM.039a, 6.x.1995 ( RMNH.MOL.42808); 1 ad., 1 juv. dry shell, sta. CAM.068a, 1.iv.1996 ( RMNH.MOL.254637); 1 ad., 1 juv. dry shell, 1 juv. in alcohol, sta. CAM.075a, 10.iv.1996 ( RMNH.MOL.254635; RMNH.MOL.254640); 1 ad. in alcohol, sta. CAM.076a, 9.iv.1996 ( RMNH.MOL.330189); 1 ad. in alcohol, sta. CAM.077a, 10.iv.1996 ( RMNH. MOL.254638); 1 ad., 1 juv. dry shell, sta. CAM.078a, 10.iv.1996 ( RMNH.MOL.254641); 1 juv. dry shell, sta. CAM.081a, 11.iv.1996 ( RMNH.MOL.254642) .

Other material examined: CAMEROON: Sud Prov .: 1 specimen in alcohol, sta. CAM. 34a, ca 250 m SW of Ebom II, 19 km S of Lolodorf, 3.05°N 10.70°E, 400 m, 5.ix.1995 ( RMNH.MOL.330325) ; 1 ad., 2 juv. dry shells, sta. CAM.86a, Nyangong , 30 km S of Lolodorf, 2.966667°N 10.73333°E, 650 m, swamp forest, 24.iv.1996 ( RMNH.MOL.330326) ; 1 ad. dry shell, sta. CAM.101a, Nyangong , 2.95°N 10.73°E, 700 m, undisturbed forest on steep, N-facing slope, 9.v.1996 ( RMNH.MOL.330327) ; 1 juv. dry shell, sta. CAM.111a, Meka’a-II, W of Nyangong , 2.966°N 10.733°E, 690 m, 18.v.1996 ( RMNH.MOL.330328) .

Distribution ( Fig. 11): Only known from two areas in Southwest Cameroon, ca 25 km distant and differing somewhat in altitude (400–500 vs 600–700 m).

Habitat: Live specimens and empty shells were collected from the understorey vegetation up to three metres above the forest floor in little disturbed rainforest between 400 and 700 m. At the type locality A. fruticicola lives syntopically with A. semenguei and A. acuminata . In the Nyangong area A. fruticicola occurs sympatrically with A. subacuminata , but the latter species was more often found on the forest floor.

Remarks: Avakubia fruticicola is quite distinct from A. avakubiensis , to which species the material had earlier been tentatively attributed (de Winter & Gittenberger 1998). The two species differ in teleoconch rib spacing, coiling tightness, width of the apical whorls, apical angle, proportional aperture and body whorl size, and whorl convexity. A. occidentalis has a proportionally smaller aperture and body whorl, and slightly wider spaced (but still comparatively close-set) ribs. A. fruticicola resembles A. crystallum in axial ribbing, but has a smaller and less cylindrical shell with more convex whorls, a less pointed apex, and a proportionally larger body whorl. A. biokoensis differs by the larger, more cylindrical shell and proportionally smaller body whorl.