Discovery of a new species Flaccisagitta yamato sp. nov. (Chaetognatha, Sagittoidea) and features of water circulation in the Yamato Rise region of the Sea of Japan

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Abstract

In the central Japan Sea, above the underwater Yamato Rise, chaetognaths (Chaetognatha, Sagittoidea) were discovered. Study of the anatomy of the specimens revealed the presence of saclike gelatinous structures (SG/S/), which indicates their belonging to the subfamily Flaccisagittinae. The features of the newly discovered species of Flaccisagitta are the distribution of fins on the body, the shape of the ciliated loop, the presence of peculiarly located ray structures and seminal vesicles relative to the caudal fin. The new species for science was named after the place of discovery above the Yamato Rise Flaccisagitta yamato sp. nov. The uniqueness of the discovery lies in the distribution of the new species – it was found only in the waters above the Yamato Rise. Hydrological data are presented on a possible explanation of the distribution of the new species, its discovery in the central part of the Sea of Japan. Modern data on the movement of water masses obtained as a result of expeditionary research and observations from space are presented, which allow us to assume the reasons for the existence of this species above the Yamato Rise.

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About the authors

Alla P. Kasatkina

V.I. Il’ichev Pacific Oceanological Institute, FEB RAS

Email: apkas@mail.ru
ORCID iD: 0000-0002-8004-9511

Doctor of Sciences in Biology, Leading Researcher

Russian Federation, Vladivostok

Vyacheslav B. Lobanov

V.I. Il’ichev Pacific Oceanological Institute, FEB RAS

Email: lobanov@poi.dvo.ru
ORCID iD: 0000-0001-9104-5578

Candidate of Sciences in Geography, Head of Laboratory

Russian Federation, Vladivostok

Aleksandr F. Sergeev

V.I. Il’ichev Pacific Oceanological Institute, FEB RAS

Author for correspondence.
Email: sergeev@poi.dvo.ru
ORCID iD: 0000-0003-4247-0791

Senior Researcher

Russian Federation, Vladivostok

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2. Fig. 1. Scheme of surface currents of the Sea of ​​Japan (according to [5]). CT – Tsushima Current; CBCT – coastal branch of the Tsushima Current; MCT – marine branch of the Tsushima Current; ECC – East Korean Current; SFC – Subpolar Frontal Current; PT – Primorsky Current; NKT – North Korean Current; MCG – main cyclonic gyre of the northern part of the Sea of ​​Japan. The 2000 m isobath is shown. The asterisk on the northern edge of the Yamato Rise marks station 12, where the holotype was collected.

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3. Fig. 2. A – General appearance of the specimen of F. yamato sp. nov: holotype, diagram (cc – ciliated loop, f – anterior fin, g – ventral ganglion, ov – ovaries, p – posterior fin, ss – seminal vesicle). Scale bar: 1 mm. B – part of the body with the anterior fin, magnified 1.5 times: holotype,F. yamato sp. nov: diagram ( r – rays). C – diagram of the eye. Scale bar: 0.1 mm.

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4. Fig. 3. Head from the ventral side: holotype, F. yamatosp. nov: holotype, photo (a – anterior denticles, b – posterior denticles, h – setae, in – intestine). Scale bar: 0.5 mm

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5. Fig. 4. Eye of F. yamatosp. nov: holotype, photo

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6. Fig. 5. General appearance of the specimen F. yamatosp. nov: holotype, photo. Scale: 1 mm

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7. Fig. 6. Body part with the hind fins of F. yamatosp. nov: holotype, photo (R – rays, SG – jelly-like structures). Scale: 1 mm

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8. Fig. 7. Water temperature distribution at the 50 m horizon for the period 21–30.04.2014 (JMA, 2024) (a). b – infrared image from the NOAA-16 satellite (n60067) for 25.04.2014. The dots indicate the positions and numbers of oceanographic stations 6–17, carried out by the R/V Akademik M.A. Lavrentyev on 21–24.04.2014. A–G – warm anticyclonic eddies. The gray tone corresponds to land and clouds. For other designations, see Fig. 1

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9. Fig. 8. Distribution of water temperature (a) and chlorophyll-a content (b) along the section carried out by the R/V Akademik M.A. Lavrentyev on 21–24.04.2014. The upper axis shows the position and numbers of oceanographic stations.

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