Anaglyphula yanseni, Chen & Páll-Gergely, 2023

Chen, Zhe-Yu & Páll-Gergely, Barna, 2023, A new species of Anaglyphula Rensch, 1932 from an island off the coast of West Indonesia, with redescription of the type species (Gastropoda: Caenogastropoda: Assimineidae), Raffles Bulletin of Zoology 71, pp. 597-605 : 602-603

Anaglyphula yanseni , new species

( Figs. 3 , 4A )

Anaglyphula sp. “Babi” Chen, 2021: 73, fig. 3.

Type material. Holotype. MZB.Gst. 23.829; 1 adult + 3 juvenile paratypes, MZB.Gst. 23.830, Pulau Babi (2°5′20″N, 96°39′5″E), Pasir Tinggi, Teupah Selatan, Kabupaten Simeulue, Aceh, Indonesia, leg. Yansen Chen, 25 Nov 2018.

Diagnosis. A tiny (shell height: ca. 1.2 mm) Anaglyphula species with pitted sculpture covering the entire surface.

Description. Shell minute, conical-ovoid, thick, somewhat opaque, 4.25 moderately convex and matte whorls; upper whorls reddish brown, lower whorls rather lighter. Protoconch with 1.25 whorls, no notable sculpture, but fine growth-lines present; boundary between protoconch and teleoconch clearly visible. Entire teleoconch surface with a faveolate structure formed by fused ribs which widen and diverge; no region on the teleoconch has parallel ribs without pits; margins with dense gradually descending sharp ridges, overall serrated-shaped; depressions (pits) irregular, round to elongated ellipsoids, tend to be divided by elongated and connected ridges. Structure near the suture and middle of the body whorl somewhat shows the original ribs the most (density is approximately five ribs per 200 μm), but even that area is pitted; umbilical region with dense radial ribs, continued with the faveolate structure. Aperture semilunar, strongly oblique to the shell axis. Peristome discontinuous, parietal callus indicated by a thin but whiten calcareous layer; peristome thickened and expanded, not reflected; the outer peristome white, expanded, with horny intermediate peristome; the inner peristome white, smooth smaller than the outer. No constriction visible in oblique view to the aperture. Both the holotype and the adult paratype have a lighter coloured line ca. half a whorl behind the aperture, but they may represent growth lines instead of the constriction. Umbilicus open, narrow, approximately 1 /9 of shell major diameter.

Operculum. Unknown.

Measurements (in mm). Shell height: 1.22, Shell width: 1.11, Aperture height: 0.47, Aperture width: 0.58 (holotype).

Habitat. Found within dead leaf litter on rocks.

Etymology. The species is named in honour of the Indonesian malacologist Yansen Chen, who discovered this new species.

Distribution. This new species is found in the type locality only.

Remarks. Only this new species, Anaglyphula sauroderma , and Anaglyphula cancellata have the rib-mesh structure on the shell surface in the known species in this genus. The new species is significantly smaller than the latter two, while the upper whorls of Anaglyphula sauroderma are more pointed. By comparing the type specimens of Anaglyphula cancellata with the new species, we believe that their rib-mesh structure is homologous. In Anaglyphula cancellata the rib-mesh structure is formed intermittently, but in the new species, it is spread over almost all of the surface. Unfortunately, we could not obtain any material of Anaglyphula sauroderma for further exploration. Anaglyphula yanseni , new species, appears to lack the constriction observed in the known species. However, this could be due to its placement being too deep to be visible from the aperture. On the lateral side of the shell, a suggestive internal thickening can be observed ( Fig. 4A ).

Some Acmella species from the Andaman and Nicobar Islands can also be compared with the new species even though the rib-mesh structure is distinctive. Acmella moreletiana G. Nevill, 1878 ( Fig. 5B , NHMUK 1891.3.17.944-7, Batti Malve, Nicobars) can be distinguished by its glossy shells. Acmella mellilla Godwin-Austen, 1895 ( Fig. 5C , NHMUK 1903.7.1.1698, syntypes, South Andaman, leg. de Roepstorff.) and Acmella roepstorffiana G. Nevill, 1878 (see Godwin-Austen & Nevill, 1879, pl. 59, fig. 5.) can be distinguished from the new species by having a dense and regular ribbed surface and shallow suture.

Figures

Fig. 3. Anaglyphula yanseni, new species, holotype MZB.Gst. 23.829. A–B, Shell; A, Visible light camera images; B, SEM images; C, Protoconch; D, Detailed structure on upper body whorl; E, Detailed structure on lower body whorl.

Fig. 4. A, Putative constriction position of Anaglyphula yanseni, new species, holotype MZB.Gst. 23.829; B, Constriction of Anaglyphula cancellata Rensch, 1932, syntype NHMUK 1897.8.3.150; C, Constriction of Anaglyphula whitteni Vermeulen, 1996, paratype NHMUK 20000247. Not to scale.

Fig. 5. Acmella species. A, Acmella cf. tersa, NHMUK; B, Acmella moreletiana G. Nevill, 1878, NHMUK 1891.3.17.944–7; C, Acmella mellilla Godwin-Austen, 1895, NHMUK 1903.7.1.1698.