Diancta batubacan Nurinsiyah, Prasetia, Mujiono & Heryanto, 2025

Diancta batubacan Nurinsiyah, Prasetia, Mujiono & Heryanto sp. nov.

Fig. 2 A – D View Figure 2

Type material.

Holotype. Indonesia • Shell H = 5.2 mm; D = 2.8 mm; ha = 2.1 mm; da = 2.1 mm; W = 7.5; North Moluccas, Bacan Is., Sumae Village ; 0°35.11'S, 127°24.19'E; alt. 54 m (M 5); 1 June 2022; Heryanto, N. Mujiono, I. W. Laitupa leg.; MZB Gst.23.855 GoogleMaps . Paratype. Indonesia • same locality as holotype; MZB Gst.23.856 / 15 GoogleMaps . Both holotype and paratypes were deposited in the Museum Zoologicum Bogoriense ( MZB).

Diagnosis.

Shell with bulbous penultimate whorl and a distinct constriction on the dorsal part of the penultimate whorl. Radial ribs are distinct before and after the constriction, but on the penultimate whorl the ribs are less distinct and almost smooth with no spiral striae. One outer parietalis, three parallel palatalis, and three perpendicular palatalis are present beside the constriction inside the penultimate whorl. Colour almost white.

Description.

The shell is small, elongated, and sinistral with a pointed apex, whitish cream in colour. The shell has 7–7.5 whorls that increase in size, with the body whorl being narrower than the penultimate whorl. There is a rapid increase in shell whorl size from the beginning of the teleoconch until the 5 th whorl, followed by a drastic constriction at the whorl 5.5–6, reducing the whorl size to that of the third whorl. The penultimate whorl (before constriction) is bulbous. The whorl size then increases again after the constriction for 1.5 whorls until the aperture. The umbilicus is closed. The protoconch is smooth, lacking ribs on the first whorl. Radial ribs are not sinuous but rather distinct, low, thin, and densely placed. The spacing between ribs increases from the beginning of the teleoconch until the 5 th or 6 th whorl, where the whorl size increases rapidly, causing the ribs to become less distinct and almost smooth. After the constriction, the ribs become more widely spaced before transitioning to a tighter spacing towards the aperture. Spiral striae are absent. A constriction is present on the penultimate whorl, with one outer parietalis, three parallel palatalis, and three perpendicular palatalis beside the constriction. The aperture is slightly oval and nearly rounded. Peristome simple because the outer and inner peristome fused. Operculum multispiral. Shell dimensions of the specimens (n = 16): H = 4.9–5.7 mm (mean 5.4 mm); D = 2.8–3.3 mm (mean 3.1 mm); ha = 2.0– 2.4 mm (mean 2.2 mm); da = 1.8–2.3 mm (mean 2.1 mm).

Geographic distribution and habitat.

The species has so far been recorded on Bacan Island, making it possibly endemic to this region. Specimens were collected from the karst forest habitat.

Remarks.

Only one species of Diancta was previously recorded from Bacan Island, Diancta torta Boettger, 1891 (Fig. 4 D View Figure 4 ). The species differs from D. batubacan sp. nov. by having prominent and more radial ribs both in the penultimate and body whorl; the shell of D. batubacan sp. nov. has a smooth penultimate whorl (almost without ribs). The aperture of D. torta is tilted and oval, while the aperture in D. batubacan sp. nov. is more rounded. The shell of D. batubacan sp. nov. is similar to D. halmaherica Greķe, 2017 which is currently known only from Halmahera Island, and D. constricta which so far only found in Ternate and Tidore islands. Compared to D. halmaherica , D. batubacan sp. nov. has a more bulbous penultimate whorl, and the ribs on the penultimate whorl are less distinct. Additionally, the aperture of D. batubacan sp. nov. is not tilted. The constriction on the penultimate whorl of D. halmaherica is more pronounced. The shell of D. batubacan sp. nov. also differs with D. constricta in having less distinct ribs, no spiral striae, and has three parallel palatalis and three perpendicular palatalis inside the penultimate whorl.

Etymology.

The species name “ batu bacan ” refers to the famous Chrysocolla mineral / stone found on Bacan Island. Known for its striking beauty, the mineral shares a similar beauty to that of Diancta batubacan sp. nov.