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

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