Monilearia (Lyrula) loweana ( Wollaston, 1878 )

Ibáñez, Miguel, Groh, Klaus, Alonso, María R. & Castillo, Carolina, 2006, The subgenus Monilearia (Lyrula) Wollaston, 1878 (Gastropoda: Helicoidea: Cochlicellidae) from Lanzarote and Fuerteventura (Canary Islands), with the description of Monilearia (Lyrula) tubaeformis sp. nov., Zootaxa 1320, pp. 29-41 : 34-35

Monilearia (Lyrula) loweana ( Wollaston, 1878)

Helix [ Actinella ] torrefacta R.T. Lowe, 1861 , 106–107 [Primary homonym of Helix torrefacta C.B. Adams, 1849 , from Jamaica ( Sagda torrefacta )]. Type locality: "Hab. in rupium facie aridissima aprica, sole occidentali calefacta, supra "Salinas" Ariae ad oram septentrionalem Caurum versus Ins. Lanzarotae, in foraminulis superficialibus basalti cis vesicularibus praesertim latitans".

Helix [ Lyrula ] loweana Wollaston, 1878 , 382–383.

Helix usurpans Furtado, 1886 , 87.

Lyrula loweana Bank et al., 2002 , 118.

Material. Four empty shells of Helix torrefacta (ZMZ 506118/4, leg. Wollaston, 1870), 34 empty shells collected between February 1980 and February 1996, in several localities of the North of Lanzarote ( Fig. 1 ).

Distribution and habitat ( Fig. 1 ). The species is endemic to Lanzarote. It can be traced between 50 and 600 m altitude, in lowland vegetation­type. It lives in the steep coastal areas from the extreme north of the island (El Risco) to the Peñas del Chache and also occurs in the young volcanic lava­streams, in Spanish named “Malpaís” (badlands). It can be found between lichens, in cracks and on the rock surface, within the Natural Reserve of the Archipelago “Chinijo” (north of the island and the surroundings islets), in the Natural Monument of La Corona, and also outside the protected areas of the island.

Description. The elegant discoidal shell ( Fig. 3 A) has a nearly flat to slightly elevated spire with a pointed apex; it embraces 4–4½ slowly growing whorls that are moderate convex, angled at the beginning of the body whorl. The suture is deeply impressed, but simple, the regularly rounded umbilicus is not very wide, but deep and open. The last eighth of the body­whorl is slightly bent downwards obliquely to the square flat ovate aperture. This has a delicate, discontinuous peristome with a non reflected, but slightly thickened lip.

The ornamentation is more pronounced on the dorsal side. There are many radial, laminar riblets crossed by 6–8 fine spiral, also laminar riblets ( Fig. 3 B–D), delimiting very numerous, small rectangular areas (reminding of honeycomb cells) which have a fragile, laciniae ­like bristle in each corner; each bristle is a prolongation of both transverse and radial riblets ( Fig. 3 D). Many of the bristles are lost in adult specimens. Each rectangular “cell” can be subdivided by more fine, spiral riblets ( Fig. 3 D), leading to the appearance of a fine reticulation. The protoconch is coloured brown with 1–1¼ whorls; at the very beginning it is smooth (approximately ¼–½ whorl), but then it is sculptured by the first radial riblets. The teleoconch is also brown, ornamented with alternating irregular lighter flames ( Fig. 3 A), which occupy approximately the same space as the brown colour. In some specimens an obscure brown spiral band can be traced beneath the periphery; the lower part of that band may be interrupted by small white dashes.

Figures

FIGURE 1. Geographical distribution of Monilearia tubaeformis sp. nov., M. multipunctata, and M. loweana. Symbols represent 1 x 1 km UTM squares.

FIGURE 3. Shell and SEM details. A – D. Monilearia loweana; A. from Valle Chico; B – D. from Mirador de Malpaso; C. Some bristles of third whorl rectangular “ cells ”; D. “ cell ” subdivisions and a line of bristles between second and third whorls; E – F, Monilearia multipunctata; E. from Barranco de Gran Valle; F. from Rosa de Zapata; G – H, Monilearia tubaeformis sp. nov. G. Holotype, from Lomo del Aceituno; H. Paratype, from Vega de Río Palmas, detail of shell ventrallateral side. Scale bar (2 mm) applies to A, E, F, G.