Okenia japonica
Baba, 1949

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

DISTRIBUTION

This species was previously known only from a few records from Japan.

PHOTO

3 specimens, 14 April 1983, Site 2.66, Round Is. (W), Mirs Bay, 3-6 m, AM C139013. Upper Photo: inset showing spiculate mantle - B.W. Darvell, Lower Photo: on bryozoan prey - B.E. Picton.

This small elongate species of Okenia has small rounded papillae along each edge of the mantle. The mantle edge and the papillae are usually pigmented white, and there is a white band along the edge of each gill, but the rest of the body is a translucent whitish colour devoid of pigmentation. This species, up to 8 mm long, has been found on encrusting bryozoans [see message #5070] but more recently it has been reported on an erect ctenostome bryozoan of the genus Amathia [see message #12651]. A description of the radula is in a separate message [message #12651 ].

  • Baba, K. (1949) Opisthobranchia of Sagami Bay. Iwanami Shoten, Tokyo. 211pp + pls.
  • Rudman, W.B. & Darvell, B.W. (1990) Opisthobranch molluscs of Hong Kong. Part 1. Goniodorididae, Onchidorididae, Triophidae, Gymnodorididae, Chromodorididae, (Nudibranchia). Asian Marine Biology, 7: 31-79
  • Gosliner, T. M. (2004) Phylogenetic Systematics of Okenia, Sakishimaia, Hopkinsiella and Hopkinsia (Nudibranchia: Goniodorididae) with descriptions of new species from the tropical Indo-Pacific. Proceedings of the California Academy of Sciences, 55: 125-161.
  • Rudman, W.B. (2004) Further species of the opisthobranch genus Okenia (Nudibranchia: Goniodorididae) from the Indo-West Pacific. Zootaxa, 695: 1-70.
Authorship details
Rudman, W.B., 2004 (December 21) Okenia japonica Baba, 1949. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/okenjapo

Related messages


Radula of Okenia japonica

December 21, 2004
From: Bill Rudman

Here is a scanning electron microscope photo of the radula of Okenia japonica.  This anatomy of this small elongate species of Okenia has recently been described in detail (Gosliner 2004 - from Okinawa, Rudman 2004 - from Hong Kong).  One point of difference is that the Okinawa animals were reported by the collector (R.F.Bolland) to live on erect arborescent bryozoans, which we now know to be a species of Amathia (see Rudman, 2004), while the collector of the Hong Kong specimens (B.W. Darvell) reported that they were found on encrusting bryozoans, and accompanying photos show a sheet-like calcified colony.  It will be useful to get further records of this species to confirm whether or not it has a wide range of bryozoan food.

In a specimen from Hong Kong (AM C139013) the radular formula is 23(+1) x 1.1.0.1.1. The innermost tooth has a broad base and a long elongate pointed cusp with up to 20 large pointed denticles along the cutting edge.  The denticles increase in size towards the tip of the cusp. The much smaller outer tooth in each half row has a broad quadrangular base with two large recurved pointed cusps

PHOTO: SEM photo of section of whole radula. Scale bar = 10 µm.  Round Is. (W), Mirs Bay, Hong Kong, 3–6m, 14 April 1983, 7 mm long preserved, AM C139013. Photo: G. Avern.

  • Gosliner, T. M. (2004) Phylogenetic Systematics of Okenia, Sakishimaia, Hopkinsiella and Hopkinsia (Nudibranchia: Goniodorididae) with descriptions of new species from the tropical Indo-Pacific. Proceedings of the California Academy of Sciences, 55: 125-161.
  • Rudman, W.B. (2004) Further species of the opisthobranch genus Okenia (Nudibranchia: Goniodorididae) from the Indo-West Pacific. Zootaxa, 695: 1-70.

Bill Rudman

Rudman, W.B., 2004 (Dec 21) Radula of Okenia japonica. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12651

Okenia japonica from Japan [1]

November 14, 2003
From: Yukari Sato


Hello Dr.Rudman,
Here are 2 photos of Okenia japonica from Zushi, Japan.

Data:
Date: 3 Aug 2003
Depth: 17m
Size: 5mm.
Location: Zushi (near Hayama), Sagami bay, Japan

Best regards,
Yukari Sato

yuks@cg7.so-net.ne.jp

Sato, Y., 2003 (Nov 14) Okenia japonica from Japan [1]. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11396

Thanks Yukari,
Bill Rudman

Rudman, W.B., 2003 (Nov 14). Comment on Okenia japonica from Japan [1] by Yukari Sato. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11396

Okenia japonica from Japan [2]

November 14, 2003
From: Yukari Sato


Hello Dr.Rudman,
Here are 2 photos of Okenia japonica from Izu Peninsula, Japan.

Data:
Date: 5 Jun 2003
Depth: 17m
Size: 7mm.
Location: Tago, Suruga Bay, west coast of Izu peninsula, Japan

Best regards,
Yukari Sato

yuks@cg7.so-net.ne.jp

Sato, Y., 2003 (Nov 14) Okenia japonica from Japan [2]. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11402

Thanks Yukari,
Bill Rudman

Rudman, W.B., 2003 (Nov 14). Comment on Okenia japonica from Japan [2] by Yukari Sato. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11402

Okenia japonica from of Hachijo Is, Japan

August 17, 2001
From: Nishina Masayoshi

Dear Dr.Rudman,

Okenia japonica is common but difficult to find because of the size.

Date: 29 June, 2001
Place: Sokodo, Hachijo Island Japan
Depth: 10m
Size: 10mm
Photos by Nishina Masayoshi

Best Regards,
Nishina Masayoshi

nishina@hpe15.wips.co.jp

Nishina, M., 2001 (Aug 17) Okenia japonica from of Hachijo Is, Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4947

Thanks Nishina,
Bill Rudman.

Okenia japonica from Hong Kong

August 17, 2001
From: Bill Rudman & Brian Darvell

Here is some information and photos on Okenia japonica from Brian Darvell's Hong Kong collections.

This small elongate species of Okenia has small rounded papillae along each edge of the mantle. The mantle edge and the papillae are usually pigmented white, and there is a white band along the edge of each gill, but the rest of the body is a translucent whitish colour devoid of pigmentation. This species, up to 8 mm long, has been found on encrusting bryozoans.

PHOTO: 3 specimens, 14 April 1983, Site 2.66, Round Is. (W), Mirs Bay, 3-6 m, AM C139013. Upper Photo: inset showing spiculate mantle - Photo: B.W. Darvell.

Hong Kong Collection Records:
AM C133749,21 March 1982, Site 1.20, Village Rock, Double Haven, 10 m. AM C139013, 3 specimens, 14 April 1983, Site 2.66, Round Is. (W), Mirs Bay, 3-6 m. AM C139014, 11 April 1983, Site 4.60, Kong Chau (NW), Mirs Bay, 5-10 m. AM C141478, 11 February 1984, Site 10.98, Kiu Tau (S), Kiu Tsui Chan, Port Shelter, 4 m. AM C150245, 2 specimens, 5 April 1986, Site 2.67, Kai Kung Tau, Kat O Chau, Mirs Bay, 6 m. AM C150246, 2 specimens, 20 April 1986, Site 2.173, Kat O Chau (E of E tip), Mirs Bay, 2 m. Depth range: 2-12 m.

Reference:
• Rudman, W.B. & Darvell, B.W. (1990) Opisthobranch molluscs of Hong Kong. Part 1. Goniodorididae, Onchidorididae, Triophidae, Gymnodorididae, Chromodorididae, (Nudibranchia). Asian Marine Biology, 7: 31-79

Best wishes,
Bill Rudman & Brian Darvell

Rudman, W.B. & Darvell, B.W., 2001 (Aug 17) Okenia japonica from Hong Kong. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5070