Avakubia biokoensis 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 : 628-630

Avakubia biokoensis de Winter & Vastenhout , sp. n.

Figs 12, 18E, F

Gulella (Avakubia) avakubiensis: Ortiz de Zárate Lopez & Ortiz de Zárate Rocandio 1956: 118 , fig. 22;

van Bruggen & Van Goethem 1997: 9.

Etymology: The species name refers to the Bioko I., where the species is likely to be endemic.

Diagnosis: Avakubia biokoensis differs from A. subacuminata in having closer-set axial ribs on the teleoconch, a less acuminate apex, less tightly coiled whorls, and a proportionally larger peristome. A. avakubiensis can be readily distinguished from A. crystallum in having a smaller shell, more pointed apex and more widely spaced teleoconch ribs. Avakubia biokoensis differs from both A. occidentalis and A. fruticicola in having larger shell with less dense teleoconch ribs.

Description:

Shell ( Figs 12, 18E, F, Table 1): Medium-sized (mean H 3.9 mm), elongate ovoid-biconical, largest width at penultimate whorl. H:D 1.68–1.91, median 1.81, in holotype 1.81. All specimens with 6 moderately convex whorls. Coiling tightness 4.33–4.47, median 4.45, in holotype 4.46. Protoconch raised but not acuminate, consisting of ca 2.0 whorls. Protoconch sculpture of holotype consists of 9–10 major spiral cords on second whorl, each 12–20 µm wide, built of poorly individualized squarish particles of very unequal length. Major cords are irregularly interspaced by thinner lines. Cords tend to be wider towards lower suture. In the RBINS paratype the spiral cords are more numerous (ca 13), and less wide, at most 8 µm. Teleoconch sculpture with relative dense, regularly spaced, curved axial ribs, about 9.8–10.8 ribs/mm on penultimate whorl, median 10.0 ribs/mm, in holotype 10.8 ribs/mm, with fine, irregular spirals in interstices. Last whorl not exceeding half the shell height, BWH 47–48 % of H, in holotype 47 %. Peristome complete, higher than wide; PH:PW 1.12–1.18, median 1.14, in holotype 1.13. PH 36–37% of H, median 36 %, in holotype 36%. PW 53–62 % of H, median 58%, in holotype 58 %. Apertural lip wide and flaring, but hardly incrassate.Two apertural barriers visible in frontal view: a weak, blunt thickening on mid-palatal wall and a projecting angular tooth that extends inwards as deeply entering lamella. Internal wall body whorl with short, deep-set palatal fold, externally visible as pale stripe in holotype ( Figs 12C, D). Columellar lamella externally not discernable in the available specimens. Umbilicus narrow but open.

Body colour: Dried tissue in holotype shell pale orange-red.

Anatomy: Unknown.

Holotype: EQUATORIAL GUINEA: Bioko I.: Basilé Bubi, ca 3.7°N 8.8°E, ca 400 m, ix.1946, Antonio Ortiz de Zárate , ex colln Altimira (see van Bruggen (1973)) ( RMNH.MOL.327295).

Paratypes (localities verbatim from label in italics): 1 ad. dry shell Basilé Bubi [ Rio Bireborico (=Bericorico?], ix.1946, Antonio Ortiz de Zárate ( RBINS 21612 ) ; 1 ad. dry shell Basilé Bubi , En Rio Borabecho , 4.iv.1954, Antonio Ortiz de Zárate ( MNCN 15.05 /26565) ; 1 ad. dry shell Basilé , Bericorico y Borabecho (orig. handwritten lable, printed museum label reads: Rios Ericorico y Borabecho, Basilé), ix.1947, Adolfo Ortiz de Zárate ( MNCN 15.05 /26569) .

Distribution ( Fig. 8): Only known from a few localities near Basilé. The species is likely to be endemic to Bioko I.

Habitat: Unknown except for a few notes by Ortiz de Zárate Lopez and Ortiz de Zárate Rocandio (1956: 118): lives in forest along a stream; a specimen from Bonyoma (see Remarks) was found in secondary forest. A. biokoensis is probably a lowland species (in contrast to A. ortizdezarateorum ), the area around Basilé lying at around 400 m.

Remarks: The apical sculpture of two specimens, the holotype and the RBINS paratype, differs in number and width of the spiral cords (studied by SEM). The sculpture of the third available specimen (studied under a stereomicroscope, 60× magnification) resembles that of the holotype, the fourth shell that of the Brussels paratype. We provisionally consider this a case of intraspecific variation.

All material of this species was originally in the collection of Adolfo Ortiz de Zárate Lopez, who exchanged Fernando Poo land snails with various professional and amateur malacologists. Only four specimens of A. biokoensis could be located for this study. Ortiz de Zárate Lopez’s collection with two specimens arrived in MNCN Madrid after his death. The best preserved, evidently live-collected, shell studied by us was originally in the collection of C. Altimira, now in RMNH. Another specimen was exchanged with the late W. Adam and is now in RBINS. Ortiz de Zárate Lopez and Ortiz de Zárate Rocandio (1956) list seven specimens from Basilé Bubi, but the collection dates differ from those on the labels of the material studied here. This suggests that the number of shells of A. biokoensis in the Ortiz de Zárate Lopez’s collection originally has been larger, the whereabouts of missing material being unclear. In RMNH, there is a copy of an unpublished list (dated March 1958, probably compiled by A. Ortiz de Zárate Lopez) of terrestrial Mollusca from Fernando Poo sent to the “Direccion General de Provincias y Plazas Africanas”, mentioning material of “ G. (A.) avakuviensis ” (sic) from Basilé Bubi. The fate of this institute’s collection appears to be unknown ( Villena et al. 1997).

Ortiz de Zárate Lopez and Ortiz de Zárate Rocandio (1956) mention a single specimen from Bonyoma that is said to differ by a smaller shell, proportionally less elongate aperture, straight outer lip and a not ascending last whorl. The whereabouts of this specimen, which might constitute still another Avakubia species on Bioko, is presently unknown. Material from the Pico de Isabel listed by these authors belongs to A. ortizdezarateorum .