Idas sinensis, Wu & Lin & Qiu & Xu & Xing, 2025

Idas sinensis sp. nov.

Figs 3 H – I View Figure 3 , 4 F – G View Figure 4

Materials examined.

Two specimens collected from the same piece of sunken wood by trawling from a seabed at a depth of 460–550 m (30.7°N, 127.8°E) in April 2023.

Type material.

Holotype • TIO 2023-1816 B 6 (length: 9.3 mm) GoogleMaps ; Paratype • TIO 2023-1816 B 21 (length: 13.4 mm), with a fractured right valve GoogleMaps .

Diagnosis.

Shells extremely thin, with internal surface color similar to external surface. Dorsal and ventral margins nearly parallel. Bristles short, brown, mainly concentrated along both sides of ridge in posterior triangular area. Shells resemble those of I. iwaotakii , but overall outline more elliptical compared to I. iwaotakii due to more similar anterior and posterior heights.

Shell morphology.

Shells 9.3 mm to 13.4 mm in length, 3.1 mm to 3.9 mm in height (Fig. 3 H – I View Figure 3 ), thin, fragile, deep olive-yellow, semi-transparent, very thin nacreous layer. Highly elongated, elliptical shape with concentric growth lines. Small specimen with rounded anterior and posterior margins; large specimen with broadly triangular posterior margins. Dorsal and ventral margins straight and nearly parallel, with slight incurvature along the ventral outline in larger specimens. Very short, dark brown bristles distributed mainly along the ridge from the posterior margin to the umbo. Umbo extremely anterior. Hinge plate slightly curved, with degenerated anterior hinge teeth (Fig. 4 F – G View Figure 4 ). Inner shell surface smooth, lacking muscle scars. Prodissoconch pink and rounded.

Soft tissue anatomy.

The soft tissue was poorly preserved to allow for detailed examination. However, the foot of the specimen preserved in alcohol was purple.

Gill-associated microbes.

Only the gill tissues of the holotype ( TIO 2023-1816 B 6 ) could be used for analysis of symbiotic microbes. Among the bacteria associated with the gill, Pseudohongiella sp. , Reichenbachiella sp. , and SUP 05 cluster were most abundant, representing 70 %, 9 %, and 7 % of the sequences, respectively (Figs 5 View Figure 5 , 6 A View Figure 6 ).

Habitat and distribution.

So far, this species has only been found within wood. It is known only from the East China Sea (30.7°N, 127.8°E).

Etymology.

The name sinensis – the Latinized form of China, refers to the type locality, within the Chinese EEZ of the East China Sea.

Remarks.

Idas sinensis sp. nov. exhibits a close morphological and phylogenetic relationship with I. iwaotakii , as both species share an elongated shell shape, characterized by nearly parallel dorsal and ventral outlines, a feature that sets them apart from Idas species in other clades. The primary difference between these species (for specimens around 1 cm in length) lies in the curvature of the anterior and posterior margins: Idas sinensis sp. nov. has a more capsule-shaped outline, while I. iwaotakii has a more triangular profile.

Additionally, the Mediterranean species Idas cristiani Fr. Giusti, Mietto & Sbrana, 2012 and Idas emmae Fr. Giusti, Mietto & Sbrana, 2012 also exhibit an elongated form. However, none of the Idas sinensis sp. nov. specimens (9.3 mm and 13.4 mm) have anterior hinge teeth, whereas I. cristiani has 5–6 small teeth below the umbo, and I. emmae has three. Moreover, Idas sinensis sp. nov. has sparser bristles compared to I. cristiani , and its shell (H / L = 0.29–0.33) is higher than that of I. emmae (H / L = 0.25–0.26) ( Giusti et al. 2012).