Re: Okadaia - Vayssierea

April 16, 2000
From: Irina Roginskaya

Dear Bill!
Okadaia elegans Baba is one of the most common nudibranch in the intertidal environment of Popov Island, Sea of Japan. In August- October 1969 I could observe there these red little creatures, just like the one displayed by Yasuhiro Shirai. Usually the masses of these molluscs were attached to sea weeds, often to Chordaria flagelliformis, and to the leaves of Zostera . Their mucous spawns, attached near by, were small, in the form of little sausages (~ 1.5 whorls). The bright orange or rosy-red eggs could be seen through the semitransparent stroma of the egg mass. Usually there were 12-16 eggs in one spawn. Our Okadaia also have direct development. In August I could find the early spawns, containing eggs before cleavage, as well as the egg masses with slowly rotating veligers, densely packed in the egg capsules (without larval shell), and also the old spawns with larvae not long before hatching. And often the crawling, just hatched, young Okadaias, transparent, slightly yellowish ,with black eyes, with body length ~0,5 mm , already bearing rhinophores, were also seen.

In aquarium the young crawling Okadaia hatched from the spawn, found in the field 20 August 1969 with uncleaved eggs, after 10 days of development (01 September 1969). At the beginning of October Okadaia were also very common, their length attained 1.5-2.1mm.

According to Baba (1937) I determined this mollusk as O. elegans Baba. I am sure we were dealing with the same species. But in 1971 L. Slavoshevskaja described this species, also from the Sea of Japan, as new - Okadaia tecticardia Slavoshevskaja, 1971, based on some anatomical differences from the specimens studied by Baba. •Slavoshevskaya L.V. (1971) A new aberrant nudibranchiate mollusc from the Sea of Japan. Explorations of the Fauna of the Seas, VIII(XVI). Fauna and Flora of the Possiet Bay of the Sea of Japan (Hydrobiological Investigations by diving method). Nauka, Leningrad. Zoological Institute of the Academy of Sciences of the USSR.

I have often seen our O. elegans floating in waves without any substrate - perhaps also the way to secure its widespread distribution? In fact it seems possible that all these red animals belong to a single species - but in 1969 I thought in another way.
Best wishes,
Irina S.Roginskaya.

Roginskaya, I., 2000 (Apr 16) Re: Okadaia - Vayssierea. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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