Zilchistrophia hilaryae Pall-Gergely

Pall-Gergely, Barna & Asami, Takahiro, 2014, Description of two new Ecuadorian Zilchistrophia Weyrauch, 1960, with the clarification of the systematic position of the genus based on anatomical data (Gastropoda, Stylommatophora, Scolodontidae), ZooKeys 453, pp. 1-17 : 2-3

Taxon classification Animalia Stylommatophora Scolodontidae

Zilchistrophia hilaryae Pall-Gergely sp. n. Figs 1 B–C, E, 2 A–H, 3 A–B, 4B, D, F, 5 A–D

Type material.

Ecuador, Pastaza Province, Chuintsa, transect 7, (samples 360-369), leg. Hilary Kingston, 17.09.2000., NHMUK 20020375.1 (holotype), NHMUK 20020375.2-10 (9 paratypes); Ecuador, Pastaza Province, Nuevo Corrientes, transect 6, 02°00.224'S, 076°45.712'W (sample 175), leg. Hilary Kingston, 11.09.2000., NHMUK 20020384/1 paratype; Ecuador, Pastaza Province, Nuevo Corrientes, transect 6, 02°00.224'S, 076°45.712'W (sample 163), leg. Hilary Kingston, 11.09.2000., NHMUK 20020385/1 paratype; Ecuador, Pastaza Province, Chuintsa, transect 7, (sample 426b), leg. Hilary Kingston, 17.09.2000., NHMUK 20020372/1 paratype; Ecuador, Pastaza Province, Chuintsa, transect 7 (samples 419-425), leg. Hilary Kingston, 17.09.2000., NHMUK 20020374/7 paratypes; Ecuador, Pastaza Province, Chuintsa, transect 7, (samples 461-466), leg. Hilary Kingston, 17.09.2000., NHMUK 20020370/6 paratypes; Ecuador, Pastaza Province, Chuintsa, transect 7, (sample 305), leg. Hilary Kingston, 17.09.2000., NHMUK 20020387/1 paratype; Ecuador, Pastaza Province, Nuevo Corrientes, (sample 200), leg. Hilary Kingston, 13.09.2000., NHMUK 20020388/1 paratype; Chuintza, Pastaza, Ecuador, sample 308, Tissue sample J5, leg. Hilary Kingston, 17.09.2000., NHMUK 20020422 (dissected, ethanol-preserved animal).

Diagnosis.

A small Zilchistrophia species with regularly growing whorls, rounded body whorl, relatively wide umbilicus and three palatal plicae approximately a half whorl behind the aperture. The uppermost two plicae are situated very close to each other, forming a single-looking plica.

Description of the shell

(Figs 1-2): Shell dextral, yellowish, glossy and translucent, smooth, only irregular, very fine growth lines can be seen; shell shape discoid, with slightly domed apical surface; whorls 6 (n=4), regularly growing, the last whorl and especially the apertural part is conspicuously wider than the penultimate whorl; body whorl rounded; whorls are separated by relatively deep suture; umbilicus relatively wide, funnel-shaped; aperture crescent-shaped, with slightly thickened peristome; parietal callus not conspicuous, present as slight, blunt thickening, its sculpture is extremely finely granulated, rather matt; in corroded shells the callus is whitish, whereas the penultimate whorl can remain translucent (in those shells the callus is better visible).

One, two or three sets of plicae are situated in various positions behind the aperture (see Fig. 2 and remarks). One set consists of three horizontal, short palatal plicae. The first two plicae are very close to each other, forming a single-looking plica.

Measurements (in mm). D: 4.1-5.0, H: 2.0-2.4 (n=3).

Description of the anatomy.

One specimen was anatomically examined (Chuintza, Pastaza, Ecuador, sample 308, Tissue sample J5, leg. Hilary Kingston, 17.09.2000., NHMUK 20020422).

Body. Foot seemingly holopod, but it was laterally very much depressed (probably also decayed internally), therefore the real morphology could not be clearly examined (Fig. 4B, 4D); caudal horn absent, jaw absent, buccal mass conspicuously elongated (Fig. 4F); the pallial complex could not be examined due to the decay of the body.

Radula (Fig. 5). Long and narrow; central tooth small, pointed oval; the central and first lateral teeth are clearly separated; lateral teeth dagger-like, 19 in number on each side in each V-shaped row; the curved cusps of the lateral teeth point toward the centre and are connected by an extension to the basal figs that point away from the centre; first lateral tooth similar in shape to the other laterals, and it is conspicuously smaller than the second lateral tooth.

Genitalia (Fig. 3 A–B). The right ommatophoral retractor runs between penis and vagina; penis long, slender, simple thin-walled tube, without any notable inner structure; penis surrounded by a thick, fibrous tunica; the end point of the penis is considered where the tunica narrows; epiphallus slightly shorter and slimmer than the penis (including the tunica), although tapers until proximal end; the short retractor muscle inserts on the epiphallus-vas deferens transition; vas deferens enters epiphallus subapically, slender, it is attached to the epiphallus almost along the complete length of the epiphallus; atrium relatively long, internally with fine longitudinal sculpture; vagina very short, it is attached to the body wall with a few fibres; inner wall of vagina finely reticulated; spermoviductus with swollen distal part with folded/reticulated inner surface; no embryos were found within the uterus; the distal end of the stalk of the bursa copulatrix forms a sheath which partly covers the vagina; the bursa copulatrix and the posterior part of the spermoviductus could not be investigated because the decayed condition of the examined specimen.

Differential diagnosis.

Zilchistrophia hilaryae sp. n. differs from Zilchistrophia shiwiarorum sp. n. by the larger size, weaker peristome, wider umbilicus, the rounded body whorl and the upper plica which consists of two joint plicae. Moreover, Zilchistrophia shiwiarorum sp. n. has more regularly growing whorls, (the apertural part is wider in Zilchistrophia hilaryae sp. n. from dorsal view). There are some differences in the anatomy between the two Ecuadorian species, such as the length of the retractor muscle and the presence or absence of the hook of the proximal epiphallus, although more material is needed to see if these represent reciprocally stable characters.

All three Peruvian Zilchistrophia species have more whorls than the Ecuadorian ones, and the area just behind the peristome margin conspicuously inflated, whereas this part is not inflated in the two new Ecuadorian species. The umbilicus of all three Peruvian species is regularly funnel-shaped with the last quarter of whorl being more far from the preceding whorl from ventral view.

Addition to this difference, The Peruvian species are larger than Zilchistrophia hilaryae sp. n. and have narrower umbilicus. Moreover, Zilchistrophia tridentata has three short palatal plicae in equal distance between each other. See also remarks.

Etymology.

Zilchistrophia hilaryae sp. n. is dedicated to Mrs. Hilary May (maiden name: Kingston), who collected the snails during the expedition to Ecuador.

Type locality.

Ecuador, Pastaza Province, Chuintsa.

Distribution

(Fig. 6). Zilchistrophia hilaryae sp. n. is known only from the vicinity of Chuintsa and Nuevo Corrientes, Pastaza Province, Ecuador.

Ecology.

The snails were collected among the leaf litter in open areas on the floor of the rain forest.

Conservation status.

Like in case of all other species inhabiting rain forest ecosystems, the main threats are deforestation and disturbance of the natural forests. The Shiwiar tribe has already called international attention, volunteering programs are focusing on them. We might assume that this would be positive in the conservation of the rain forest inhabited by the Shiwiar tribe.

Remarks.

The plicae can be observed in case of fresh, translucent shells only. Although in some corroded shells a single set of plicae is visible behind the aperture, we have not depicted them on Fig. 2, because additional sets of plicae may be present deeper in the shell, which are invisible due to the non-transparent shell wall. Even in crystal clear shells there might be plicae other than in the last whorls, but these cannot be observed without breaking the shell. Regardless of the difficulties in observing the inner plicae, it seems that juvenile shells have three sets of plicae, approximately a third whorl distance between each other. We assume that the previous sets of plicae (or some of them) are dissolved during growth.

We examined the inner morphology of the plicae in a subadult shell by breaking a part of less than a quarter of whorl off (Fig. 1C). The upper plica (=plica closer to the upper suture) was “double”, by having the upper and lower edges more elevated than its middle portion, and the lower plica (=plica closer to the lower suture) was “simple”. The shell of the anatomically examined specimen had to be broken, which offered the possibility to examine the inner side of the palatal wall. The upper plica in fact consists of two plicae which are situated close to each other and are in contact (Fig. 1E). This results the strange concave shape of the upper plica from apertural view.

A part of the shell of the paratype of Zilchistrophia tridentata bearing two of the palatal plicae is deposited in the Senckenberg Museum (SMF 162900). On that shell fragment both of the plicae were simple.