Author: (Rudman, 1985)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 15 mm

Sightings: Sunshine Coast

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Goniobranchus rubrocornutus (Rudman, 1985)

This small dorid, 7 – 15 mm in length, is not commonly recorded. Although described in 1985 recent molecular sequencing and morphological examination, published in Soong et al, 2022, has identified a different colour variation within the species. They have determined that these variations are sympatric morphotypes and designated them as morphotypes A & B of the species.

Morphotype A matches the original description by Rudman, 1985.

The generalised common characteristics for both morphotypes of Goniobranchus rubrocornutus include:
– An oval elongated body having a smooth notum without tubercles.
– A white notum without spots or other markings.
– Either 2 or 3 marginal bands of differing colours – arrangement varying with morphotype.
– Translucent deep red rhinophores and gills – see morphotypes for varying edging detail.

The two morphotypes are differentiated as follows:
A: Translucent creamy white notum; three marginal bands: outermost orange band, then an irregular red band, finally an irregular opaque white band; gill and rhinophores are translucent deep red with either red or white edges.
B: Opaque white notum; outermost red band, then a yellow band, both of equal widths; gill & rhinophores translucent deep red with bluish white edges.

The reversal of the red and orange marginal band position in the two morphotypes is an interesting variation. From the molecular sequencing undertaken there were no genetic differences revealed between the two morphotypes “(uncorrected pairwise distance = 0.0%)”.

Distribution: Widely distributed around tropical and subtropical Indo-Pacific.

Originally described as Chromodoris rubrocornuta Rudman, 1985.

David A. Mullins – July 2023 

References:
– Rudman, W. B., (1985). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris aureomarginata, C. verrieri and C. fidelis colour groups. Zoological Journal of the Linnean Society. 83: 241-299.

– Rudman, W. B., (2000, December 30). Chromodoris rubrocornuta Rudman, 1985. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/chrorubr and associated messages.

– 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)

– Gosliner, T. M., Valde ́s, A ́. & Behrens, D. W. (2018). Nudibranch & Sea Slug Identification – Indo-Pacific, 2nd Edition. New World Publications, Jacksonville, Florida, USA.

– Soong, G. Y., Bonomo, L. J., Reimer, J. D. & Gosliner, T. M. (2022). Battle of the bands: systematics and phylogeny of the white Goniobranchus nudibranchs with marginal bands (Nudibranchia, Chromodorididae). ZooKeys 1083: 169–210. https://doi.org/10.3897/zookeys.1083.72939