Hemicycla (Hemicycla) laurijona, Alonso, María R. & Ibáñez, Miguel, 2007

Alonso, María R. & Ibáñez, Miguel, 2007, Anatomy and function of the penial twin papillae system of the Helicinae (Gastropoda: Helicoidea: Helicidae) and description of two new, small Hemicycla species from the laurel forest of the Canary Islands, Zootaxa 1482, pp. 1-23 : 6-9

Hemicycla (Hemicycla) laurijona sp. nov.

Type locality. Barranco de Aramaqué, La Gomera (UTM: 28R BS8114, 1000 m altitude).

Holotype ( Fig. 4 A). TFMC (MT 0392); leg. M.R. Alonso and M. Ibáñez, 15th February 1985.

Paratypes. 45 paratypes collected between 1985 and 2006 (14 specimens, bodies preserved in ethanol and 31 shells): CHC (7 paratypes: 6 specimens, bodies preserved in ethanol, and 1 shell); TFMC (1 paratype: MT 0393) and AIT.

Etymology. The name “ laurijona ” is a combination of the first five letters of the Spanish term “laurisilva” (= laurel forest) and the first four letters of the name “Jonay”, the lover of Gara (The Garajonay National Park, in La Gomera, is named after both mythical lovers.).

Distribution and habitat ( Fig. 1 ). The species is endemic to La Gomera. It occurs at an altitude of 700– 1280 m in the National Park of Garajonay and its surroundings. The live specimens ( Fig. 3A ) were mainly found under moss on the trunks of trees in the laurel forest.

Description. Body dark-brown coloured, sole pale-brown. The shell (Table 2; Figs. 2 A, 3A, 4A,B, 5A–C) is imperforate, slightly depressed globular, with 3¾–4¼ low convex whorls and shallow sutures. The aperture is oblique, without angulations and rounded in the palatal zone. The white peristome is only slightly reflected in a lip in the palatal zone, whereas it is well reflected in the columellar zone, covering the umbilicus. The shell has a small, weak and wide radial costulation combined in the body whorl, with an also weak malleate surface sculpture. The shell surface is glossy, brilliant, with highly variable colouring. Some specimens are pale-brown, others dark brown; some are uniform, slightly reddish and others pale greenish coloured. In some specimens there are four, in others five spiral, darker bands: two-three dorsal bands narrow or wide, sometimes interrupted, and two ventral narrower and more uniform. In many specimens, all the bands are interrupted, forming irregular patches that fuse with those of the neighbouring bands, giving the shell a multicoloured appearance.

Genital system (Fig. 6A–C; 3 specimens dissected): Atrium short. The bursa copulatrix complex in the female genital system shows a moderately short diverticulum, slightly longer than the bursa copulatrix duct. The latter is slightly shorter than the common stalk and slightly swollen distally, shortly before entering the proximal vagina. The bursa copulatrix is rather small and globular, with its neck inserted into the diaphragm. The dart sac is accompanied by a pair of branched tubular mucus glands.

The male portion of the genital system shows a penial complex with a very long flagellum, about 4–5 times longer than the distal male duct (i. e. that part of the penial complex between the retractor muscle insertion and the atrium). The penis sheath is very thin, translucent and poorly visible. The retractor muscle has an epiphallar insertion. The length proportions between the above mentioned male and female ducts are similar to those of the immature specimen shown in Fig. 6B.

The penis has a system of twin papillae with a penial chamber between them (Fig. 6C). The penial chamber has pleated walls and is in fact the chamber of the distal penial papilla. The connection between the distal penial papilla and the penis wall is sometimes visible from the exterior (Fig. 6B) and we named it as the “ring zone”. A well developed contact organ is located between the distal penial papilla and the atrium.

Remarks. The species most similar to H. laurijona in shell shape and shell dimensions is H. perraudierei ( Figs. 4 C, 5D–F) from El Hierro, the westernmost, youngest and smallest island of the archipelago, about 60 km distant from La Gomera.

H. laurijona generally has a slightly smaller and more depressed shell than H. perraudierei (Figs. 4,5,7), and also a weaker shell malleation ( Fig. 5 ), but the main morphological difference between both species is found in the female part of the genital organs, namely in the length of the stalk of the bursa copulatrix complex. The stalk in H. laurijona is, in fact, similar in length to that of the bursa copulatrix duct and of the diverticulum (Fig. 6A,B), whereas in H. perraudierei it is nearly twice as long (Fig. 6D,E). Both species also differ in their microhabitat. H. laurijona lives under moss on the tree trunks in the laurel forest of La Gomera, whereas H. perraudierei was found at a similar altitude (600–1100 m), in the upper area of the degraded laurel forests of El Golfo and Tiñor (El Hierro), among the leaves of Aeonium sp. and also among fallen dead leaves.

Figures

FIGURE 1. Geographical distribution of Hemicycla laurijona sp. nov. and Hemicycla fulgida sp. nov. The blue arrow indicates approximately the area of the Hemicycla invernicata type locality. Symbols represent 1 x 1 km UTM squares.

FIGURE 2. Shell drawings. A. Hemicycla laurijona sp. nov. holotype. B. Hemicycla fulgida sp. nov., holotype showing the placement of the measurements obtained. BH, body whorl height (at columella level); BP, body whorl frontal perimeter; BS, body whorl frontal surface (plane view); D 1, maximum shell diameter; D 2, shell diameter perpendicular to D 1; FP, shell frontal perimeter; FS, shell frontal surface (plane view); SH, shell height; SP, shell perimeter (dorsal plane view); SS, shell surface (dorsal plane view).

FIGURE 4. Shells. A. Hemicycla laurijona sp. nov., holotype. B. Hemicycla laurijona sp. nov., paratypes from Puntas Coloradas, La Gomera. C. Hemicycla perraudierei, from Las Casillas, El Hierro.

FIGURE 5. Shell body whorl details. A – C. Hemicycla laurijona sp. nov., holotype. D – F. Hemicycla perraudierei. A, D, dorsal view. B, E, frontal view. C, F, ventral view. The sells are the same as in Fig. 4.

FIGURE 3. A. Hemicycla laurijona sp. nov., paratype from Puntas Coloradas, La Gomera. B. Hemicycla fulgida sp. nov., paratype from El Bailadero, Tenerife.