Okenia pellucida
Burn, 1967

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

DISTRIBUTION

New Zealand, Australia (NSW, Qld,  WA), Hawaii, Japan, Palmyra Atoll,  Malaysia; United Arab Emirates  (See Rudman, 2004).

PHOTO

Angourie, North Coast, New South Wales, Australia. March 1982, 3 specimens 8, 12 & 20mm long, on Zoobotryon. PHOTOS: Bill Rudman.

The animal is elongate with up to 11 or 12 lateral papillae along each side of the mantle edge, which forms a distinct ridge around the edge of the notum. There are also a few papillae [5-6] on the dorsum, but they do not seem to form a consistent pattern. The head is quite separate from the foot and bears large triangular oral tentacles. The rhinophores are about twice the length of the mantle papillae. The gills are bipinnate and form a circle, or incomplete arch around the anal papilla.

The whole of the body is translucent white with a network pattern of thin dark brown lines covering all parts of the dorsum, the foot,  the head and the rhinophores stalk.  In some specimens the lines also extend to the tips of the mantle papillae. There is often a brownish band around the bottom half of the rhinophore club, and the gills have a thin brown line along each rachis.

The anatomy of this species has recently been re-examined (Gosliner, 2004; Rudman, 2004). Photos of the radula are posted separately [see message #12648 ]. Since its original discovery in Sydney Harbour 40 years ago, this species is now known from much of the Indo-West Pacific. It is always associated with the ctenostome bryozoan Zoobotryon verticillatum on which it feeds and lays its egg masses. This bryozoan is a common fouling organism which suggests that wide distribution of this nudibranch has probably been aided by shipping.

• 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.
• 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.

ARCHIVE NOTE:  An earlier edition of this Fact Sheet [5 Oct 1999] is available on request. 

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