Diancta phoenix Bochud, 2021

Bochud, Estee, Haberthuer, David, Hlushchuk, Ruslan & Neubert, Eike, 2021, A new Diancta species of the family Diplommatinidae (Cyclophoroidea) from Vanua Levu Island, Fiji, ZooKeys 1073, pp. 1-12 : 1

Diancta phoenix Bochud sp. nov.

Figs 1 -4

Type locality.

Fiji, Cakaudrove Province, Vanua Levu Island, Vatumuvamode Mountain, Savusavu, - 16.65°N, 178.53°E 63 m a.s.l. (original label text).

Type material.

Holotype. MCZ 394198 ex coll. Otto Degener., leg. Otto Degener, 6.1.1941. 1 shell, SH = 2.59, SW = 2.85, AH = 1.34, AW = 1.57, W = 6.25. The protoconch and peristome are the only remaining parts of the broken shell.

Etymology.

The new species is named after the immortal saga bird that arises from its ashes. The species epithet is derived from the bird’s name: Phoenix. It is a noun in apposition. Despite the broken holotype, this species is being kept “alive” by pictures, 3D prints and Micro-CT scans.

Description.

shell sinistral, tiny (SH = 2.59 mm); pyramidal shaped; consisting of 6.25 whorls separated by a shallow suture; protoconch dull, smooth, 2.5 whorls; surface of teleoconch shell with radially aligned, regularly and finely formed axial ribs; ribs slightly curved; last whorl bears sharper ribs, ribbing pattern less regular, with a larger spacing between ribs; whorls rapidly increasing in size, shell constricted after four whorls; constriction site prominent, forming a bulge situated one whorl behind the aperture at the umbilicus; change of coiling axis after zone of constriction, turning the shell 45 degrees upward towards the apex; aperture large, about half shell height, slightly oval shaped and attached to the shell; two visible teeth located in the aperture; one small upper palatal tooth, and opposite a somewhat elongated basal tooth; peristome simple and continuous; inside shell, above ventral bulge, with an elongated palatal lamella opposite the very narrow constriction; columellar plate reduced; umbilicus closed.

Distribution.

This species is known so far only from the type locality.

Remarks.

According to the original label (Fig. 4 ), the shell was found in a place interpreted as Vatumuvamode on Mount Savu Savu. Close to the city of Savusavu in the South of Vanua Levu, there is a hill named Suva Suva. On topographic Fijian maps dated 1985, this hill is called mount Nasuvasuva (352 m a.s.l.). We were unable to allocate the mountain Savu Savu or a place called Vatumuvamode. It is difficult to say whether Degener’s Savu Savu is a misspelling of Nasuvasuva, or whether he meant another place. The exact meaning of Vatumuvamode is also unclear. In the northwestern part of the island, a place called Savu Sau exists. A path leads from there to the Vuadomo waterfalls, reminiscent of Vatumuvamode. Since the shell was found in 1941 during World War II, and at a period when Fiji was a British colony, it is very likely that names of the places changed since then, or it belongs to an old village or defence site that is not shown on maps. However, the label and its interpretation seem contradictory and unresolvable. Additional sampling of more localities is needed to locate the exact type locality of the new species.

The shell was already quite eroded. The boundary between the protoconch and teleoconch is not clearly visible, while several ribs are partially removed or degraded. There is also no recognizable colouring on the shell. Because other shell specimens and living animals of this species are lacking, it raises the question whether the specimen studied could be an aberrant shell of a species that has already been described. In any case, it is not possible to perform a comparative study on the morphology of shells, operculum, radula, and/or genitalia.

Other genera of Diplommatinidae with a directional change of the coiling axis include Moussonia O. Semper, 1865, Opisthostoma W. T. Blanford & H. F. Blanford, 1860, Plectostoma H. Adams, 1865, and Whittenia T.-S. Liew & Clements, 2020. Moussonia monstrificabilis Greķe, 2017 changes coiling direction from dextral to sinistral, which is not the case in the newly described species. The aperture in Opisthostoma points towards the apex or the dorsal side of the shell due to an alteration in the coiling axis ( Nurinsiyah and Hausdorf 2017). This is not seen in Diancta phoenix sp. nov. In addition, the doubled peristome, mentioned in the original description of Opisthostoma by Blanford (1860), is missing. Usually, Plectostoma has a detached last whorl ( Kobelt 1902; Egorov 2013; Liew et al. 2014b) and an "extraordinary prolongation backwards of the free portion" ( Adams 1865). This is not the case for D. phoenix sp. nov. Liew and Gopalasamy (2020) described the new genus Whittenia , which conchologically resembles Opisthostoma but differs by the outer whorl being raised above the level of the apex, and distinguishing it also from our specimen. None of these character state combinations applies to the new species. In contrast, the penultimate whorl of the shell is constricted, as originally described by von Martens (1864) for the genus Diancta . Due to the upward bend in coiling, the last whorl wraps once again around the constricted whorl and gives a pyramidal appearance to the shell. In Opisthostoma and Plectostoma , the coiling axis changes, but, more importantly, the aperture ends detached from the shell or points in an upwards or other direction to that of the shell axis. For this reason, we assign the new species to Diancta .

Differential diagnosis.

Applying the key of Neubert and Bouchet (2015) to the new species, identification attempts lead to the species D. rotunda Neubert & Bouchet, 2015, due to the sinistral shell and reduced columellar plate. This species has a small palatal fold deep in the aperture and a shell height of 2.6 mm in the same size range as D. phoenix sp. nov., but it clearly differs by its quite bulbous penultimate whorl. Other species that are similar in size are D. macrostoma (Mousson, 1870) and D. martensi (H. Adams, 1866). With their strongly ascending last whorl, these two species are reminiscent of an incipient change in the coiling axis, as is the case for the newly described species. However, the missing shell features in the new species are the alteration of the coiling axis and the presence of frontally visible apertural teeth. The peristome of Diancta phoenix sp. nov. is simple and not doubled as in the other described species (Fig. 5 ).

Several species of Fijian Diancta , like D. macrostoma and D. martensi , share a strong ascending last whorl and a similar ribbing pattern. Diancta phoenix sp. nov. is distinguished from all Fijian species by the clear coiling axis twist of 45 degrees, the presence of a simple peristome, the umbilical bulge, its simple columella and the two teeth present in the aperture. To evaluate the variability of these traits, more specimens must be sampled. Changes in the coiling axis are documented for different snail groups and seem to have independently evolved several times ( Páll-Gergely and Neubauer 2020).

Figures

Figure 4. original label from 1941 by Otto Degener and the interpreted label by MCZ, Harvard.

Figure 1 A, B. Diancta phoenix sp. nov. Holotype, MCZ 394198, SH = 2.59 mm A Different external views of the shell B Micro-CT views.

Figure 5 A-D. Comparison of D. phoenix sp. nov. with other Fijian species A D. phoenix sp. nov., with simple peristome, SH = 2.59 mm B D. rotunda Neubert and Bouchet, 2015, with bulbous penultimate whorl, SH = 2.65 mm C D. macrostoma (Mousson, 1870), SH = 2.84 mm and D D. martensi (H. Adams, 1866), SH = 2.62 mm, with strong ascending last whorl and double peristome.