Okenia distincta
Baba, 1940

Order: NUDIBRANCHIA
Suborder: DORIDINA
Superfamily: ANADORIDOIDEA
Family: Goniodorididae

DISTRIBUTION

Known from northern Japan (Baba, 1940) and eastern Russia (Martynov, 1997 [see #21314 ]; Chernyshev, 2007 [ see #21293]).

PHOTO

Locality: Peter the Great Bay, intertidal, Russia, Pacific Ocean, Japan Sea, 1 October 2007, Intertidal. Length: 3-4 mm. Photographer: A.V. Chernyshev

Small elongate species with up to ten papillae along each side of the mantle edge and scattered papillae over the dorsum. The papillae are relatively short with a slightly inflated, rounded tip. The rhinophores are described by Baba as 'cylindrical, perfoliate'. In colour the animal is a translucent straw colour with an opaque mottling of cream and brown. It is reported to feed on the bryozoan Amathia [Chernyshev, #21293 ]

In general shape and colour, it is similar to Okenia zoobotryon, which feeds on Zoobotryon sp. and O. mija which feeds on a species of Amathia. However both of these species have a few distinctive cup-shaped lamellae on the rhinophores, while O. distincta apparently has many simple lamellae.

The radula, with a large inner denticulate tooth and a smaller bicuspid outer tooth (Baba, 1940) is very similar to both O. mija [#12638] and Z. bootryon [#16797, #12656].

  • Baba, K. (1940)  Some additions to the nudibranch fauna of the northern part of Japan. Bulletin of the Biogeographical Society of Japan, 10 (6): 103-111.
  • Martynov A.V. 1997. Subclassis Opisthobranchia. [In:] Kussakin O.G, Ivanova M.B., Zurpalo A.P. et al., Eds. The list of animals, plants and fungi of the intertidal of Far-Eastern Seas of Russia. Vladivostok, Dalnauka: 77-80.
  • Martynov A.V. 1998. Subclassis Opisthobranchia. [In:] Adrianov A.V., Kussakin O.G, Eds. Taxonomic catalogue of biota of Peter the Great Bay, Japan Sea. Vladivostok, Dalnauka: 204-209.
  • Martynov A.V. 2006. Nudibranchia. [In book:] Yu.I. Kantor, A.V. Sysoev. Marine and brackish water Gastropoda of Russia and adjacent countries: an illustrated catalogue. Moscow: KMK Scientific Press Ltd., pp. 268-294, plates 131-138.
Authorship details
Rudman, W.B., 2007 (December 13) Okenia distincta Baba, 1940 . [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/okendist

Related messages


Re: Okenia distincta from eastern Russia

July 22, 2008
From: Alexei Chernyshev

Concerning message #21293:

Dear Bill,
Yurii Minichev was the first Russian malacologist who found this species in Peter the Great Bay, but he mistakenly identified it as Okenia angelensis (see Minichev, 1976). Alexander Martynov (1997) re-identified O. angelensis sensu Minichev as O. distincta Baba. I send you drawing of Okenia distincta from Minichev's work: you can see that rhinophores lack lamellae. I also didn't observe any trace of lamellae.

  • Martynov A.V. (1997) Subclassis Opisthobranchia. In: Kussakin O.G., Ivanova M.B., Tsurpalo A.P. et al. A check-list of animals, plants and fungi from the intertidal zone of Far Eastern seas of Russia. Vladivostok, Dalnauka: 77-80 (in Russian)
  • Minichev Yu.S. (1976) Subclass Opisthobranchia. Animals and plants of Peter the Great Bay. Leningrad, Nauka: 92-95 (in Russian)

With bests,
Alexei

tsher@bio.dvgu.ru

Chernyshev, A.V., 2008 (Jul 22) Re: Okenia distincta from eastern Russia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21727

Thanks Alexei,

Bill Rudman

Re: Okenia distincta from eastern Russia

February 6, 2008
From: Alexander Martynov

Concerning message #21293:

Okenia distincta Baba, 1940 in Peter the Great Bay, Japan Sea

Okenia distincta is not a poorly known species and has a quite long history of study as well as misidentifications in Peter the Great Bay. This species here was firstly discovered by Minichev in 1960s, and further shortly described and figured by him (Minichev, 1976) under the name of a North American species Okenia angelensis Lance, 1966. In frames of my thorough study of the Peter the Great Bay opisthobranchs in second part of 80s and in 90s, I rediscovered this species and found out that it differs considerably from Okenia angelensis in external features as well as in the radula structure. Further checking of the Japanese literature, revealed that it was in fact Baba's species, Okenia distincta, described from Northern Honshu. External characters, i.e. ca. 10 subcylindrical or club-shaped lateral notal processes, off-white colour with brown patches on the dorsal side, and especially morphology of the radular teeth (second laterals are distinctly bicuspidate with conspicuous inner fold), described in the first description of Okenia distincta well agreed with the features of the Peter the Great Bay specimens and thus it was listed for the first time for this region under the name Okenia distincta in Martynov (1997, 1998). Morphology of the rhinophores is somewhat variable in Peter the Great Bay specimens of Okenia distincta - for instance I have found specimens which possess one entirely smooth rhinophore and another one with very weak lamellation. These variations likely refer to the vestigial nature of the rhinophoral lamellae in Okenia distincta. The characteristic cup-shaped rhinophoral structures as in, for instance, Okenia zoobotryon (Smallwood, 1910) and Okenia mija Burn, 1967 are absent in Okenia distincta. Unfortunately, publication data of Okenia distincta in these two lists were mistakenly recorded as Baba, 1941. However, this error was further improved in the recently published first comprehensive illustrated catalogue of all Russian nudibranchs (Martynov, 2006).

  • Baba K. 1940. Some additions to the nudibranch fauna of the northern part of Japan. Bulletin of the Biogeographical Society of Japan, 10(6): 103-111.
  • Martynov A.V. 1997. Subclassis Opisthobranchia. [In:] Kussakin O.G, Ivanova M.B., Zurpalo A.P. et al., Eds. The list of animals, plants and fungi of the intertidal of Far-Eastern Seas of Russia. Vladivostok, Dalnauka: 77-80.
  • Martynov A.V. 1998. Subclassis Opisthobranchia. [In:] Adrianov A.V., Kussakin O.G, Eds. Taxonomic catalogue of biota of Peter the Great Bay, Japan Sea. Vladivostok, Dalnauka: 204-209.
  • Martynov A.V. 2006. Nudibranchia. [In book:] Yu.I. Kantor, A.V. Sysoev. Marine and brackish water Gastropoda of Russia and adjacent countries: an illustrated catalogue. Moscow: KMK Scientific Press Ltd., pp. 268-294, plates 131-138.
  • Minichev Yu.S. 1976. Subclass Opisthobranchia. [In:] A.V. Zhirmunskiy, Ed. Animals and plants of Peter the Great Bay. Leningrad-Moscow, Nauka: 92-95.

Alexander Martynov

sasha_martynov@inbox.ru

Martynov, A., 2008 (Feb 6) Re: Okenia distincta from eastern Russia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21314

Thanks Alexander,

Best wishes,
Bill Rudman

Okenia distincta from eastern Russia

December 13, 2007
From: Alexei Chernyshev

Dear Bill,
Okenia distincta Baba, 1941 is a little known species described from Japan. It is not uncommon in Peter the Great Bay (Japan Sea). This species lives and feeds on bryozoans from the genus Amathia.

Locality: Peter the Great Bay, intertidal, Russia, Pacific Ocean, Japan Sea, 1 October 2007, Intertidal. Length: 3-4 mm. Photographer: A.V. Chernyshev

Best regards,
Alexei

tsher@bio.dvgu.ru

Chernyshev, A.V., 2007 (Dec 13) Okenia distincta from eastern Russia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21293

Dear Alexei,

Thanks very much for these photos. This has been to me a mysteru species which I have knon only from Baba's short description of a single specimen from northern Japan. In general shape and anatomy it seems to have similarities to both Okenia zoobotryon and O. mija  but the rhnophores in O. distincta seem to have simple lamellae rather then the cup-shaped structures in the other two species. Baba does not describe the lamellae and they are difficult to see in your photos so I would be grateful if you could confirm this difference.

You cite the description as Baba, 1941 but the publication I have is dated 1940. Have you some evidence or reference to show the publication was not published until 1941?

  • Baba, K. (1940)  Some additions to the nudibranch fauna of the northern part of Japan. Bulletin of the Biogeographical Society of Japan, 10 (6): 103-111.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Dec 13). Comment on Okenia distincta from eastern Russia by Alexei Chernyshev. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21293