Avakubia Pilsbry, 1919

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 : 617-618

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Avakubia Pilsbry, 1919


Genus Avakubia Pilsbry, 1919 View in CoL View at ENA

Etymology: Pilsbry’s name refers to the village of Avakubi in the DRC, where the type was found. Gender feminine.

Type species: Gulella (Avakubia) avakubiensis Pilsbry, 1919 , by orig. des.

Description: Shell small, with 5–7 regularly coiled whorls, adult height 3.0– 5.8 mm, ovate or elongate-ovate, diameter of the penultimate whorl always exceeds that of the body whorl.Apex rounded to strongly acuminate. Coiling tightness varies substantially between species (W: ln H=3.1–5.0). Body whorl height takes up 38–56 % of H, varying substantially between species. Peristome height 29–40 % of H. Peristome width 44–62% of D. Aperture roundish or heart-shaped with a palatal tooth or swelling, which may be inconspicuous or virtually absent, and a protruding angular tooth that continues as an inrunning lamella for nearly a whorl. Body whorl with a deep-set palatal fold, which is generally not visible in the aperture, but appears in translucent specimens as a short white line, without a corresponding external depression. Columella with a tooth or lamella, which is externally (usually) not discernable. Umbilicus narrow, but always open. Umbilicus of juvenile specimens open and rounded, decreasing in diameter with increasing shell height. Aperture of juvenile shells edentate. Protoconch with 2–2½ whorls, sculptured by ca 9–16 spiral cords of roundish or rectangular particles on the second whorl; some species have fine spiral lines in between major ones. Transition of protoconch to teleoconch marked by a rather abrupt change in sculpture. Teleoconch with strong, more or less curved, axial ribs that run from suture to suture, the interstices with fine spiral lines that do not seem to cross the axial ribs. Teleoconch spirals are not a continuation of the spiral cords on the protoconch, being more close-set, more irregular and structurally different (solid, not made up of particles).

Anatomy ( Figs 6, 15, 24; based on dissections of few specimens (singletons, except for A. acuminata ) of three different species, supplemented with information from unpublished drawings of a dissected specimen of A. avakubiensis kindly supplied by B. Rowson (NMW)): Salivary gland single. Penis more or less elongate, the basal portion widest. Internal penial wall distally without obvious pilasters in some species (present in

A. avakubiensis , not studied in A. fruticicola ), which exhibit instead irregularly shaped, larger ( A. subacuminata ) or smaller ( A. acuminata ), irregularly-shaped tissue pads. The convolute vas deferens widens more or less abruptly into a wider, rather muscular and shining terminal portion (epiphallus?). This terminal portion bends across the upper penis, and enters the penis somewhat laterally, cutting off a short apical caecum. The long penis retractor muscle originates from the columellar muscle and inserts on and/ or laterally of the penial apex, extending under the terminal portion of the vas deferens close to its entrance. Penis of most species with a lateral diverticulum (rather indistinct or absent in A. fruticicola ), which appears to consists of a fleshy structure within the penial envelope. In the penis of three species (not studied in A. fruticicola ) no spines or denticles were observed. In the lower penis of a specimen of A. acuminata , an elongate spindle-shaped spermatophore-like structure was encountered. Female genital tract with a short but distinct vagina, followed by a narrow free oviduct. In two specimens of A. acuminata , the oviduct is inflated into a pouch­like uterus, containing a single shelled embryo, so at least this species is ovoviviparous. Bursa copulatrix (gametolytic gland) with a long narrow duct and an ovoid or round bursal sac, which reaches the albumen gland. Hermaphrodite duct with a long, convolute tube-like diverticulum (talon). Radula ribbon very long relative to its width; after maceration the radula ribbon appears transversely folded in two portions of unequal length. Radula typical carnivorous, with a small number (<20 teeth in half a row) of elongate, sharply pointed, curved lateral and marginal teeth. Rachis present in A. acuminata , noticeably smaller than other teeth, not observed in other species.

Species included: In addition to the type species, A. acuminata ( Thiele, 1933) ; A. biokoensis de Winter & Vastenhout , sp. n.; A. crystallum de Winter , sp. n.; A. fruticicola de Winter & Vastenhout , sp. n.; A. occidentalis de Winter , sp. n.; A. ortizdezarateorum de Winter & Vastenhout , sp. n.; A. semenguei de Winter & Vastenhout , sp. n.; A. subacuminata de Winter & Vastenhout , sp. n.

Distribution ( Fig. 3): Cameroon, DRC, Equatorial Guinea (Bioko I.), Gabon, Ghana, Uganda.

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