Ceratosoma gracillimum C. Semper, 1876

Description

A large Ceratosoma; the living animal reaches 14 cm in length, with body height to the apex of the dorsal horn nearly 5 cm, the frontal veil about 2 cm wide and the distance between the lateral-lobe tips about 4 cm. The ground colour is pale greenish-grey, largely replaced on the upper surface and sides by large greenish-olive-grey blotches with somewhat diffuse margins, forming 4-5 broad transverse bands on the tail. Innumerable red or red-brown dots are scattered over the whole animal; the rims of the frontal veil and of the dorsal lobes are edged with a narrow red or red-brown line. Rhinophores and gill take the ground colour. Alcohol-preserved animals lose all colour, becoming uniformly pale yellowish-grey or whitish-yellow. Rhinophore club about 2.25 mm tall with 21-25 lamellae. Compared to C. cornigerum the form is overall slightly more slender.

Distribution

Type locality: Mare philippinense, Lapinig Channel near Bohol, Philippines. The species is now also known from Vietnam, the Great Barrier Reef, and Japan, broadly across the Indo-West Pacific.

Etymology

The specific epithet gracillimum is the neuter superlative of Latin gracilis ("slender, slim, graceful") — "the slenderest" — referring to the more slender body form of this species compared to its congeners C. cornigerum and C. trilobatum.

Remarks

The name gracillimum was a manuscript name written on the original specimen label and formally published in the species description.

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References

• Ceratosoma gracillimum Semper in Bergh, 1876, Rudman W.B. (1988). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: the genus Ceratosoma J. E. Gray. Zoological Journal of the Linnean Society. 93(2): 133-185. https://doi.org/10.1111/j.1096-3642.1988.tb01532.x
• ケラトソマ・グラキリムン, 殿塚孝昌. (2003). ウミウシガイドブック〈3〉. TBSブリタニカ.
• ミナミニシキウミウシ（新称）, 小野篤司. (2004). 沖縄のウミウシ. ラトルズ.
• Ceratosoma gracillimum, Johnson R.F. & Gosliner T.M. (2012). Traditional taxonomic groupings mask evolutionary history: a molecular phylogeny and new classification of the chromodorid nudibranchs. PLoS ONE 7(4): e33479.