Antonietta janthina is a colourful species of sea slug or aeolid nudibranch, a marine gastropod mollusc in the family Facelinidae.Bouchet, P.; Gofas, S. (2012). Antonietta janthina Baba & Hamatani, 1977. Accessed through: World Register of Marine Species on 2012-06-05
Distribution This nudibranch is known from south-east Japan.Rudman, W.B., 2006 (April 11) Antonietta janthina Baba & Hamatani, 1977. [In] Sea Slug Forum. Australian Museum, Sydney. For decades, a similarly coloured species found in Indonesia, the Philippines and Thailand was thought to be a tropical variant,Rudman, W.B., 2009 (October 26) Antonietta cf. janthina [In] Sea Slug Forum. Australian Museum, Sydney. however it is now known to be the separate species Trinchesia nakapila.Kim, A. Y., Donohoo, S. A. & Gosliner, T. M. (2024). Stirring up the muck: the systematics of soft-sediment Fionidae (Nudibranchia: Aeolidina) from the tropical Indo-Pacific PeerJ. 12: e18517: 1-55., page(s): 31, figs 4D, 8A-D, 9A-FKorshunova T.; Fletcher K.; Martynov A. (2025). The endless forms are the most differentiated—how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case Zoological Journal of the Linnean Society, Volume 204, Issue 4, August 2025, zlaf057,
Description Antonietta janthina has a whitish body with white surface pigment. The numerous cerata have a blue digestive gland inside them and superficial yellowish or white pigment covering the tips. The oral tentacles are bright orange-yellow and there is a median band of the same colour on the head. The rhinophores are scarlet with a median band of white.
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