Okenia mija
Burn, 1967
Order: NUDIBRANCHIA
Suborder: DORIDINA
Superfamily: ANADORIDOIDEA
Family: Goniodorididae
DISTRIBUTION
South-eastern Australia (Tasmania, Victoria, New South Wales).
PHOTO
Blackmans Bay, Derwent River, Hobart, Tasmania, subtidal on ctenostome bryozoan Amathia wilsoni, [see lower photo] 18 November 1986, [many hundreds seen] approx. 12mm long, AM C151776. Photos: Bill Rudman
The animal is small, elongate with a distinct mantle edge bearing a series of about 7 lateral papillae which are spindle shaped when fully extended, being slightly wider in the mid-region than at the base, and tapering to a rounded tip. However the shape is somewhat variable within an individual and in stressed animals the papillae can be cylindrical in shape, often with a slightly swollen tip. In some animals there is an irregular row of up to 6 papillae on each side of the body, and there are also many dorsal papillae of varying size. The rhinophores are about twice the length of the lateral papillae and have up to 6 characteristic cup shape structures on the upper half two-thirds, each having a notch in the posterior mid-line.
The body is translucent clear with a faint brownish tinge from the underlying visceral mass and a fine dusting of brown over the skin. There are also small opaque white patches scattered over the body and particularly in a band around the mantle edge creating a whitish border in some specimens. The white patches also form an irregular line down the dorsal midline. On the dorsum and sides of the body there are scattered yellowish brown irregular shaped patches, each with a dark brownish black spot, which is often but not always, in the centre of the patch. The lateral papillae appear white, especially at the tip, from a concentration of these white patches, and the rhinophores are translucent clear except for white patches on the cup-shaped lamellae. The gills are transparent except for scattered white and brown patches. A description of the radula is posted separately [message #12638 ].
Okenia mija seems to be one of a number of small brownish species of Okenia found in south-eastern Australia, but unfortunately apart for this species and Okenia zoobotryon, too few specimens of the other species or 'forms' are available to determine their status. Externally Okenia mija can be distinguished by the mantle ridge which runs all around the body, the. The relatively short and dorsoventrally flattened lateral papillae, the arrangement of the dorsal papillae and the distinctive shape of the rhinophore lamellae. Two distinctive features of the colour pattern are a translucent clear band around the mantle edge with many opaque white specks, and large light brown patches each with a central dark brown spot which are scattered over the dorsum and the sides of the body.
I have found it feeding on the ctenostome bryozoan Amathia wilsoni. Kirkpatrick 1888 in Tasmania.
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Burn, R. (1967). Descriptions of two new species of Okenia (Nudibranchia, Doridacea) from south-eastern Australia. Proceedings of the Royal Society of New South Wales 1965-66: 52-57.
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Rudman, W.B. (2004) Further species of the opisthobranch genus Okenia (Nudibranchia: Goniodorididae) from the Indo-West Pacific. Zootaxa, 695: 1-70.
ARCHIVE NOTE: An earlier edition of this Fact Sheet [17 Feb 1999] is available on request.
Authorship detailsRudman, W.B., 2004 (December 21) Okenia mija Burn, 1967. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/okenmija
Related messages
Okenia mija from Port Stephens, NSW
November 20, 2009
From: Leanne and David Atkinson
Concerning message #14768:
Dear Bill,
We found this nudibranch on Saturday evening and think it is Okenia mija. Is our identification correct?
Locality: Fly Point, Port Stephens-Great Lakes Marine Park, Port Stephens , 12 metres, New South Wales, Australia, Pacific Ocean, 15 November 2009, Sandy bottom sponges, bryozoans, gorgonias, soft corals, hydroids and ascidians. Length: 5 mm. Photographer: Leanne and David Atkinson.
Regards,
Leanne & David Atkinson
atk@hunterlink.net.au
Dear Leanne and David,
Thanks for these great photos of the rarely reported Okenia mija. I think we can say that the yellowish patches, each with a dark spot, will turn out to be a good identifying character of this species
Best wishes,
Bill Rudman
Okenia mija from Bare Island, Sydney
September 17, 2005
From: Nicholas Missenden
Hello Bill,
Could you please identify this nudibranch for me.
I believe it is some form of Okenia possibly Okenia zoobotryon.
Locality: South Wall, Bare Island, Sydney. Botany Bay, NSW, Australia. Depth: 11 m. Length: 15 mm.10 September, 2005. Broken reef, sandy bottom. Photographer: Nicholas Missenden
Regards
Nick
njmpm@iinet.net.au
Missenden, N.J., 2005 (Sep 17) Okenia mija from Bare Island, Sydney. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/14768
Dear Nick,
This is Okenia mija. These little brown species of Okenia are difficult to identify but the little brown spots usually have a translucent ring around them in this species. We don't know a lot about the biology of these species but I suspect we will find that many of them feed on particular bryozoans. I have found this one feeding on Amathia wilsoni, and although it may be wishful thinking, I think the bryozoan in your photo is Amathia.
Best wishes,
Bill Rudman
Radula of Okenia mija
December 21, 2004
From: Bill Rudman
To accompany the updated Fact Sheet on Okenia mija here is some information on the radula. It is fairly typical for the Family Goniodorididae, with a large denticulate inner lateral tooth and a small outer tooth on each side of the midline, in each row. The radular formulae of the illustrated radula is 22 x 1.1.0.1.1. The innermost tooth has a broad base and a long elongate pointed cusp with many (12 -14) broad pointed denticles along the cutting edge. The much smaller outer teeth have a broad quadrangular base with a large recurved bicuspid tip. Below the bicuspid tip, on the outer edge, there appears to be a triangular projection.
PHOTO: SEM of section of right side of radula. Blackmans Bay, Hobart, Tasmania, Australia, 18 November 1986, AM C151776. Scale bar = 10 µm. Photo: A.C.Miller.
Okenia mija and the equally small Okenia zoobotryon, are very similar in colour and size, but as I have discussed on the Fact Sheet there are some consistent differences between the two species. The radular morphology also shows some distinct differences. In Okenia mija there about approximately 12 short broad denticles on the inner teeth while in Okenia zoobotryon the denticles are longer, narrower, and more numerous. Both species have bifid cusps on the outer teeth but they are much smaller in O. mija, and there is a triangular pointed flange below the cusps, a feature absent in O. zoobotryon. The two species also seem to differ in their food bryozoan, O. mija being found on Amathia wilsoni, and O. zoobotryon always being reported from Zoobotryon verticillatum (see Rudman, 2004).
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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 mija. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12638Re: Okenia mija
February 18, 1999
From: Ross Armstrong
Hi Bill
Thanks for the quick id. There were two or three Okenia mija that I saw on the dive so there probably is a healthy little population there.
regards
Ross
Ross@northpower.co.nz
Armstrong, R., 1999 (Feb 18) Re: Okenia mija. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/581Okenia mija - new record for New Zealand?
February 17, 1999
From: Ross Armstrong
Hi Bill
This unknown nudibranch was taken at Pigeon Island, Dusky Sound, Fiordland [southern New Zealand] in late January 1999. It was tiny, approx 3-5mm. I found it and a couple others on a kelp frond in about 8m during the day.
Regards
Ross
Ross@northpower.co.nz
Armstrong, R., 1999 (Feb 17) Okenia mija - new record for New Zealand?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/576Dear Ross,
This is quite an interesting find. To my knowledge this has not been recorded from New Zealand before. It is almost certainly Okenia mija, a small species known from southern Australia.
Bill Rudman.
