Thuridilla cf ratna is similar to T. bayeri, but it lacks the blue and often yellow colors of that species. It was common at Enewetak Atoll and has been found occasionally at Kwajalein. Specimens are usually seen on or under dead coral or rubble on lagoon reefs and pinnacles. Ten measured specimens ranged in length from 13 to 25mm. Thuridilla cf ratna was first reported in the Marshalls from Enewetak and Kwajalein Atolls as Elysia ratna by Johnson & Boucher (1984). We also found specimens at Utirik and Rongelap Atolls. Our ID on this species remains uncertain. The original description by Marcus (1965) is of a single specimen from Palau, and it appears that his color description is of the preserved specimen. His only mention of the rhinophore coloration is "black on sides, light, in preserved specimen cream, in middle." His drawing, again of a preserved specimen, seems to show contracted rhinophores colored somewhat similar to those in the first photo below. Martín-Hervás, et al (2021) examined and identified as T. ratna specimens from Taiwan, the northern Marianas, the Philippines, Malaysia and Papua New Guinea but also determined through molecular data that there are three very similar, apparently undescribed species with few external features to separate them. One differentiating character they give is the coloration of the rhinophores; the one they designated as T. ratna has rhinophores black with white longitudinal lines and orange tips. The rhinophores of our specimens look more like (but not exactly) those of one they called T. sp. 7, reported as having black tips, a narrow orange band (mostly or entirely lacking in ours) followed by a noticably wider white band.
Created 22 January 2007
Updated 20 October 2021