Monilearia (Lyrula) tubaeformis Alonso & Groh

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 : 37-39

Monilearia (Lyrula) tubaeformis Alonso & Groh , sp. nov.

Type locality. Lomo del Aceituno, Fuerteventura (UTM: 28RES 8839, 350 m altitude).

Holotype. TFMC (MT 0390); leg. M.R. Alonso and M. Ibáñez, 30 Dec 1993.

Paratypes. 127 paratypes (56 ethanol specimens and 71 shells, collected between 1987 and 2004), CGH (42 paratypes), CKW (38 paratypes) and AIT (47 paratypes).

Etymology. The name tubaeformis refers to the shell form, resembling a bugle.

Distribution and habitat ( Fig. 1 ). The species is endemic to Fuerteventura. It occurs at an altitude of 300–600 m, in dry open areas of arid subtropical shrub and small ravines, mostly with Euphorbia balsamifera Aiton, 1789 , mainly under stones.

Description. Soft body brownish, the dorsum moderately darker than the sides. Shell (Table 2; Fig. 3 G) with a flat or even sunken spire, and with a twice significantly angulated periphery. It embraces about 3½ whorls, separated by an only slightly impressed suture. The umbilicus is eccentric, deep and very wide. The last quarter of the body­whorl descends considerably in respect to the prior quarter, the last part becoming completely separated from the coil, being bended down — and outwards and widened a bit (approx. 0.2–0.25 mm), resembling the bell of a tuba and showing some variability in its length and inclination ( Fig. 4 ). The aperture is well rounded, only with a small angulation in its outer edge. The peristome is free, its edges all around slightly reflected, forming a narrow white lip approximately 0.25 mm wide. The peculiar ornamentation of the teleoconch is of the Lyrula type ( Fig. 3 H) but very much developed, being stronger at the lateral and ventral parts of the shell. At the dorsum it is formed by numerous fine radial riblets which bear in regular intervals raised glossy lobulations which are placed such that they give the appearance of 5–6 spiral costulations that form a reticulation with the radial riblets. The lateral and ventral part exhibits 8–9 significant spiral lobulated ribs, which are not interrupted by the radial riblets; in the contact zone between a spiral rib and each two radial riblets, a nodule is differentiated ( Fig. 3 H). Additionally, between each two contiguous spiral ribs there are several fine, regular spiral riblets which are crossed by the radial riblets. The protoconch is slightly prominent, brown, with 1–1¼ whorls, initially smooth (approximately ¼–½ whorls) and its distal part bearing fine radial riblets. The teleoconch is coloured light brown, patterned with narrow, darker, irregular radial flames.

FIGURE 5. Drawings of genital systems. A. Monilearia tubaeformis sp. nov., paratype from Vega de Río Palmas; B–C. Monilearia multipunctata ; from Casas de Ugán; C. genital system with the distal male duct duplicated; A1–A5, parts of the vaginal stimulator appendix (terminology after Schileyko, 1984: 39, fig. 18); a, atrium; bc, bursa copulatrix; e, epiphallus; f, flagellum; p, penis; r, retractor muscle; sp, spermoviduct.

The kidney measures less than half of the lung length; secondary ureter extremely short, almost absent.

Genital system (Fig. 5A; 3 specimens dissected): Atrium similar in length to distal male duct (between atrium and penis retractor muscle insertion), which measures about ½ of the length of the proximal portion of the epiphallus and ½ than that of the flagellum. The penis retractor muscle inserts at the epiphallus. The penis is slightly widened. The vagina is very short, its diameter similar to that of the free oviduct. The duct of the bursa copulatrix is long. The branched glandular portion (A 5) of the vaginal stimulator appendix is split into two digit­like, thin ducts that are slightly longer than the A4 portion.

Remarks. The special shell ornamentation of M. tubaeformis and M. multipunctata is of the same type as that of Helix loweana , being a synapomorphy of these species. Because of this, the three species are placed in the supraspecific taxon Lyrula .

The genital system of M. tubaeformis and M. multipunctata is of the same type as that of M. phalerata and M. inops , indicating that Lyrula is a subgenus of the genus Monilearia , whose phylogenetic relationships within the family Cochlicellidae were recently established ( Ibáñez et al. 2003).

M. tubaeformis is a species unambiguously different from all of the other Cochlicellidae species because of its very distinctive shell characters. It is less adapted to the driest conditions than M. multipunctata , which also colonized the Jandía Peninsula ( Fig. 1 ). M. tubaeformis lives at a higher altitude, with more environmental humidity. It has been unable to cross the desert­like barrier of sand dunes occupying the isthmus of the Jandía Peninsula (“El Jable”) to colonize the South of the island.

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.

FIGURE 4. Monilearia tubaeformis sp. nov. paratypes, showing the shell variability. A – B. from the type locality; C. from Vega de Río Palmas.