Flabellina affinis

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Flabellinidae (Order: Nudibranchia; Suborder: Aeolidina)

Flabellina from the Latin flabellum meaning fan; affinis from Latin meaning similar. The name (similar to a fan) refers to the dorsal cerata of the animal.

50 mm.

It has a pink body with violet hues. The head carries two pairs of tentacles: those of the bottom are touch organs while the rhinophores at the top are used to detect smell. 

The rhinophores are violet, lamellated and have about 15 horizontal rings each, laid perpendicular to the axis of this appendix, something characteristic of this species.

The cerata are also violet and are distributed in 7 or 8 groups, each attached to a lateral appendix or peduncle, which protrudes from the body. The top third of each cerata has a more intense colour than the rest and the red to dark orange digestive gland can be seen inside. The rhinophores are flat instead of annulate.

Flabellina affinis is distinguished from the similarly looking Flabellina ischitana by an opaque violet zone just under the cnidosac at the tip of each ceras and  from Flabellina pedata by having a smaller number of cerata which end in white tips, become less in number as they progress to the tail, and protrude directly from the body, lacking the base peduncles of the cerata. (1)

This species is a hermaphrodite.

Considered to be endemic in the Mediterranean and the near by Atlantic coasts. Usually found at depths of 5m - 20m. Prefers rocks in shady areas with moderate flow.

1.027-1.032  

8° C - 22° C. (can be kept constantly at 18^oC)

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Prefers subdued lighting.

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Carries cnidosacs containing the stinging cells of Eudendrium hydrarians. May be dangerous to other fish. According to R. Shimek they are not reef safe due to their high predatory potential and skillfulness in finding hiding places in a tank. (2)

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Needs live food. Eats eudendrium sp.  The urticant cells or cnidosacs of the polyps are stored at the tip of the cerata; these are referred to as cleptocnidia (stolen utricant cells). This forms the defence system of the nudibranch. The cerata detach during an attack and release the active cnidosacs thus deterring the attacker. The cerata are replaced by the animal.

Hermaphrodite. The eggs are deposited as a violet ribbon around the hybroids on which the animals feed. As the shells of the larvae develop the egg ribbon loses some of its colour, becoming light pink.