Nembrotha cf. chamberlaini  Gosliner & Behrens, 1997

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cf. is an abbreviation from a Latin word (confer) and means 'refer to' or 'compare with', here it means it could possibly be Nembrotha chamberlaini or perhaps something closely related, or at least similar in appearance.
More informations on Nembrotha cf. chamberlaini are at Bill Rudman's Sea-Slug Forum!