Discus (Canaridiscus) laurisilvae Allgaier & Klemm, 2012

Allgaier, Christoph & Klemm, Matthias, 2012, Discus (Canaridiscus) laurisilvae sp. nov., a species from the laurel forest of La Gomera, Canary Islands (Gastropoda: Pulmonata: Discidae), Zootaxa 3224 (1), pp. 62-66 : 63-65

publication ID	https://doi.org/ 10.11646/zootaxa.3224.1.5
persistent identifier	https://treatment.plazi.org/id/A970EF1A-BC21-4D2A-FF24-F8F9FCD17BF1
treatment provided by	Felipe
scientific name	Discus (Canaridiscus) laurisilvae Allgaier & Klemm
status	sp. nov.

Treatment

Discus (Canaridiscus) laurisilvae Allgaier & Klemm View in CoL , sp. nov.

Figs. 1 A,D View FIGURE 1 ; 2A–D View FIGURE 2

Diagnosis. A large-sized Discus species (shell diameter up to 15.2 mm) if compared to all the Discidae known from Macaronesia, with a striated shell, whorls rounded at periphery, with wide umbilicus and low spire; penis long, but less than half of the length of the penis of D. saproxylophagus .

Remarks. The genus Atlantica Alonso & Ibáñez, 2011 is based on insufficient evidence, as the anatomical characteristics of the type-species of this genus, Atlantica gueriniana from Madeira is unknown ( Rähle & Allgaier 2011; Yanes et al. 2011). We therefore provisorily herein maintain the status of the genus Discus with the subgenera Atlantica and Canaridiscus ( Bank et al. 2002).

Description. The shell is comparatively large, rather solid, depressed, with a low spire and rounded periphery or sometimes slightly subangulate periphery when young. The specimens are evenly horn-colored, mature shells are mostly largely denuded. Upper surface weakly ribbed and ribs almost obsolete on the body whorl below the periphery. Fully grown shells have up to 6.5 whorls, slowly increasing. The shell is up to 7.4 mm high and up to 15.2 mm wide. Umbilicus broad, deep, between 35 % and 40 % of the shell, exhibiting all of the whorls inside. The whorls visible inside the umbilicus lack ribs. Spire with convex outlines and deep sutures. Protoconch consists of 1.75 smoothish, horn colored whorls, suture impressed. Aperture rounded oval, the peristome is simple ( Figure 1 View FIGURE 1 , A).

Genital system. ( Figure 2 View FIGURE 2 , A–D; one specimen dissected, deposited in SMNS (ZI0088751); SDi (shell diameter): 13.8 mm; SH (shell height): 6.3 mm )). In the following description, the terms "distal" and "proximal" are used in relation to the hermaphroditic gland. Atrium short ( Figure 2 View FIGURE 2 , A, B). Penis long and compactly coiled ( Figure 2 View FIGURE 2 , C). When expanded its length reaches approximately 43 mm. It is 2.3 times longer than the complete female part of the genital system with vagina, oviduct, spermoviduct and albumen gland. Proximally, the penis is thicker than distally. The long penial retractor muscle is quite massive at its insertion site on the penis. The vas deferens is linked to the atrium by a perpendicular connective tissue sheet 2 mm before the vas deferens opens into the penis. The distance of the vas deferens from the penis to the attachment site at the atrium is relatively short, with a remarkably narrow passage, if compared to the three other species of the taxon Canaridiscus ( Figure 2 View FIGURE 2 , B). The pedunculus of the small bursa copulatrix is long and thin. The pedunculus joins the oviduct just in front of the atrium thus resulting in a short vagina. The free oviduct is four times longer than the vagina ( Figure 2 View FIGURE 2 , D). The albumen gland is well developed and has a short talon ( Figure 2 View FIGURE 2 , A).

Holotype ( Figure 1 View FIGURE 1 , A; empty shell): collected by M. Klemm, 17 th February 1992, SMNS ( ZI0088750 ).

Paratypes. Same locality, collected by M. Klemm, 17 th February 1992; 1 alcohol specimen, SMNS ( ZI0088751 ); 5 empty shells, SMNS ( ZI0088752 ); 2 empty shells, SMF ( SMF 336667 View Materials /2); Bosque del Cedro , near the village El Cedro, collected by W. Rähle and T . Beck, 4 th March 2005; 3 empty shells (1 intact, 2 fragmentary), SMNS ( ZI0088753 ) .

Type locality. La Gomera, Bosque del Cedro , Laurisilva, approx. 300 m north of the chapel Ermita de Nuestra Señora de Lourdes, in the steeply sloping valley of the Cedro creek at an altitude of 900 m a.s.l., 20–30 m to the west of the creek (28°07'46"N, 17°13'12"W) GoogleMaps .

Etymology. The species name refers to the habitat of the species.

Habitat and distribution. Up to now, the new species is only known from the type locality. The shells were found between the roots of old trees or underneath stones and rotten leaves. In the same locality, D. saproxylophagus (Alonso, G. Holyoak & Yanes) (verified anatomically), and D. ganodus (Mabille) were present.

Comparison with the other Discidae species known from Macaronesia. Apart from D. laurisilvae sp. nov., there are two more Discidae species of comparable shell size hitherto known from Macaronesia, D. rupivagus Rähle & Allgaier 2011 and D. saproxylophagus , both from La Gomera. D. rupivagus has a smaller, very flattened, sharply keeled shell with strong, regular ribs inside the umbilicus and differs clearly from the new species D. laurisilvae sp. nov. D. saproxylophagus is very similar to D. laurisilvae sp. nov. in shell size and shell height ( Fig. 1A, B View FIGURE 1 ). In both species, the shell surface texture is quite similar. Concordantly, the whorls inside the umbilicus are radially striated ( Fig. 1 View FIGURE 1 , D, E). Nevertheless, there are markedly distinctive morphological features of the shell and of the genital anatomy. The primary shell difference between D. laurisilvae sp. nov. and D. saproxylophagus is the pronounced keel of the latter. Additionally, both species display highly significant differences with respect to the the index-variables UD/SDi (umbilicus diameter / shell diameter) and AH/AB (aperture height) / AB (aperture breadth) and the parameter AB (aperture breadth) [see Table 1]. Significant differences were observed concerning the parameters UD (umbilicus diameter) and NW (number of whorls). D. saproxylophagus has a smaller umbilicus, which measures between 25 % and 30 % of the shell diameter, in D. laurisilvae between 35 % and 40 % ( Tab. 1; Fig. 1 View FIGURE 1 , A, B). Obviously, the proportion of UD to SDi provides the best discriminating character for both species ( Fig. 3 View FIGURE 3 ), but also the shape of the aperture of both species is significantly different. In D. saproxylophagus , the shell aperture is angularly ovate in contrast to D. laurisilvae sp. nov., which has a rounder aperture. Furthermore, the shell outlines in the lateral view exhibit differences of the two species. D. saproxylophagus has a more dome-shaped spire and less convex whorls, whereas the spire of D. laurisilvae sp. nov. is less elevated but the whorls have more convex outlines ( Fig. 1 View FIGURE 1 , A, B).

Anatomically D. laurisilvae sp. nov. has a much shorter penis than D. saproxylophagus . Although the dissected specimens are of comparable shell size to each other (dissected specimen D. laurisilvae sp. nov. SDi: 13.8 mm; D. saproxylophagus SDi: 14.2 mm), its penis does not reach half of the length of the penis of D. saproxylophagus , but it has a similar diameter. The vas deferens sequence from the penis to the attachment site at the atrium is considerably shorter in D. laurisilvae sp. nov., about one third of the distance in D. saproxylophagus . The vas deferens of D. laurisilvae sp. nov. becomes remarkably thin in this region compared to other Discidae of the taxon Canaridiscus , however, this may be a trait that needs further confirmation from more specimens.