Marine life  /  Nudibranchs & sea slugs  /  Okenia
Reviewed 2026-09-06
Species entry

Okenia

Okenia

Small goniodorids with a fringe of papillae round the mantle, on bryozoan and ascidian crusts.

Size
5 to 20 mm
Depth
3–25 m
Habitat
Bryozoan and ascidian crusts on rubble
Active
Day and night
Range
Indo-Pacific
Rarity
Lembeh Strait
4 stars of 5, two or three a season
SP-01
okenia · full body · habitat
4:3 · min 2400px

Small dorids, most between five and twenty millimetres, with an elongate body that is narrower than the sole of the foot and a margin carrying a row of long slender papillae down each side. Several taller papillae usually stand along the midline in front of the gill. The gill itself is a small plume of a few branches set well back, and the rhinophores are lamellate and cannot be withdrawn into pockets. Ground colour runs translucent white, cream, orange or pink, generally with darker pigment spots on the body and on the tips of the papillae.

The genus feeds on bryozoans and on colonial ascidians, and the animals are found on the encrusting sheet rather than on open ground. Productive surfaces are the undersides of rubble, dead shell, jetty legs and any hard object that has been in the water long enough to carry a crust. Spawn is a short white coil laid on the same sheet, and it is often what draws attention first.

The genus is large, a good many of the animals photographed on these coasts are not matched to a described species, and records from a dive normally stay at the genus. At this size the practical limit is not identification but finding the animal at all, and a productive patch of bryozoan usually holds more than one. Recorded from about 3 to 25 m.

Where to find:

LocationRarity Best monthsDepthHabitat
Lembeh Strait Indonesia editorial estimate
4 stars of 5, two or three a season
Year-round
3–25 m
Bryozoan and ascidian crusts on rubble
Anilao Philippines editorial estimate
4 stars of 5, two or three a season
Year-round
3–25 m
Encrusting growth on rubble
Dauin & Dumaguete Philippines editorial estimate
4 stars of 5, two or three a season
Year-round
3–25 m
Rubble and jetty structure
Bali Indonesia editorial estimate
4 stars of 5, two or three a season
Year-round
3–25 m
Encrusting growth on rubble
Ambon Indonesia editorial estimate
4 stars of 5, two or three a season
Year-round
3–25 m
Harbour structure and silty rubble

Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.

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