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| Clione japonica Tomoyasu, Hiroshi & Jing, 2025 |
Abstract
We describe a new cryptic species of Clione from intermediate and deep waters of the Japan Sea (East Sea) and from shallow coastal waters of the southern Okhotsk Sea. Diagnosis is based on a suite of stable morphological traits—particularly laterally extended foot lobes and a broader central radular tooth—with c oxidase subunit I (COI) data providing supplementary support. Maximum likelihood analyses of the COI dataset resolved two sister clades: specimens from the Japan Sea (East Sea) occurred only in the clade that also contains the new species, whereas specimens from the southern Okhotsk Sea occurred in both. In contrast, Automatic Barcode Gap Discovery, applied to the same alignment, recovered a single molecular operational taxonomic unit (MOTU) consistent with shallow divergence and the lack of a clear barcode gap. As COI distances from C. okhotensis Yamazaki & Kuwahara, 2017, are modest, we rely primarily on morphology and reciprocal monophyly for species recognition, with COI data playing a supplementary role. We hypothesize that hydrographic structure and Late Quaternary isolation of the Japan Sea (East Sea) shaped this lineage, and that its occurrence in the Okhotsk Sea reflects transport by regional water masses. The new species highlights hidden diversity in pelagic pteropods and the role of semi-enclosed seas in fostering regional differentiation.
Keywords: Clione, COI gene, gymnosomata, Japan Sea (East Sea), taxonomy
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| The new species Clione japonica sp. nov., holotype (SMRZ M20): A, front view; B, dorsal view; C, right-side view; D, left-side view <scale bars: 2 mm (A–D)>. |
Family CLIONIDAE Rafinesque, 1815
Genus Clione Pallas, 1774
Clione japonica sp. nov.
Diagnosis. Body with three ciliated rings (anterior, mid-body, tail region). No space between head tentacles and mouth. Lateral foot lobes ellipsoidal and extending outward. Visceral mass bright orange to red, occupying much of the anterior body (Figure 2, Figure 3B). Radula with broad central tooth and protruding lateral expansions (Figure 4, Figure 5).
Etymology. The species name japonica refers to the location of first discovery, the Japan Sea (East Sea).
Distribution. Known from deep waters of the Japan Sea (East Sea) (JSPW and JSIW) and shallow waters of the southern Okhotsk Sea.
Yamazaki Tomoyasu, Shimada Hiroshi and Zhang Jing. 2025. A New cryptic Species of Clione (Gastropoda) in deep waters of the Japan Sea (East Sea) and shallow waters of the southern Okhotsk Sea. Journal of Asia-Pacific Biodiversity. In Press, DOI: doi.org/10.1016/j.japb.2025.10.002 [7 November 2025]
