Okenia nakamotoensis
(Hamatani, 2001)

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

DISTRIBUTION

This species is known from the Kuroshima Island (Japan), Indonesia, Bohol and Cebu Islands (Philippines), and Enewetak and Kwajalein Atolls (Marshall Islands) (see Gosliner 2004). Also reported in the Forum from western Indian Ocean [message #11504 ].

PHOTO

Upper: SE Sulawesi, September, 1997. Photo: Bernard Picton. Lower: Philippines. Size: about 3 cm, Depth: about 20 m, Feb. 1997. Photo: Georg Heinze

NOTE:This animal was previously known on the Forum as Hopkinsia nakamotoensis.

It is a deep (carmine) red with rhinophores and gills of the same colour. The outer surfaces of the stalks of the gills are opaque and white and all dorsal appendages are whitish though the distal third is coloured with a deep red. The pallial margin is absent. The head is broad and forms a shield-like projection in front of the rhinophores. Five pairs of appendages are symmetrically arranged along the dorsal margin, a single appendage being present in the midline in front of the branchial gills. No oral tentacles have been observed. It has three small, simply pinnate, non-retractile gills. It grows to approximately 20mm long alive.

The radula is of a peculiar form for the Goniodorididae.  The inner lateral teeth are extremely thin and elongate and have a hooked tip. They lack denticles. The outer laterals are small and reduced with an anteriorly directed cusp. See separate message [message #12637 ] for photo of radula.

In coloration this species closely resembles O. rosacea MacFarland, 1905, and O. hiroi Baba,1938, but this species has a lower number of dorsal appendages. The radular teeth are similar to those of H. rosacea but are more slender. It is also very similar in colour to  O. kondoi but has a much broader body and bulbous dorsal appendages. The radula is also quite different. Gosliner (2004) places this species, and related species of Hopkinsia, in the genus Okenia. It is very similar on colour to O. kondoi which shares the same geographic range and the same bryozoan prey, Tropidozoum cellariforme Harmer, 1957, but differs in having a more slender shape and in radular morphology. It also differs from that species in having 5 pairs of dorso-lateral processes rather then 4. A similar species pair from northern Australia, O. stellata and O. hallucigenia have recently been described (Rudman, 2004).

• Hamatani, I. (2001) Two new species of Goniodorididae (Opisthobranchia; Nudibranchia) with a new genus from Kuroshima Island, Okinawa, Japan. Venus, 60(3): 151-156.
• 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 [14 February 2002] as Hopkinsia nakamotoensis is available on request

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