Author: Soong & Gosliner, 2022

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 18 mm

Sightings: Anilao Philippines

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Goniobranchus fabulus Soong & Gosliner, 2022

Goniobranchus fabulus has long been a cryptic species within Goniobranchus preciosus (Kelaart, 1858). Molecular sequencing and morphological examination, published in Soong et al, 2022, identified this separate species and revealed a grouping of species with a “white body and variously coloured marginal bands”. These species “…. G. verrieri, G. rubrocornutus, G. preciosus, G. fabulus sp. nov., G. daphne, and G. sinensis, …., formed a well-supported monophyletic clade (1/98%).” There are features of their external appearance that if carefully examined allow differentiation of these seemingly similar species.

Soong et al, 2022 have identified two morphotypes of this species, designated as morphotypes A & B.

The generalised common characteristics for both morphotypes of Goniobranchus fabulus include:
– An oval body having a smooth notum without tubercles.
– An opaque white notum without spots or other markings.
– Four marginal bands of differing colours.
– Rhinophore stalks are without pigment.

The two morphotypes are differentiated as follows:
A: Four marginal bands – outermost opaque bluish-white followed by deep red then yellow, and finally opaque white, all of equal widths; gills & rhinophores reddish purple with white edges.
B: Four marginal bands – outermost speckled opaque white followed by deep red then yellow, and finally opaque white; gills & rhinophores reddish purple with white edges and opaque white speckling.

The external difference in appearance between the two morphotypes is slight, being restricted to the white speckling exhibited on the outermost marginal band and over the gills and rhinophores. There was little by way of genetic difference found in the molecular sequencing within Goniobranchus fabulus.

Interestingly, Goniobranchus daphne is identified genetically as a sister species to Goniobranchus fabulus even though the former is only found in Australian waters.

Distribution: Mainly tropical western and southern central Pacific – Philippines, Japan, PNG, New Caledonia, Tonga, Vanuatu, Australia and Fiji.

David A. Mullins – July 2023

References:
– 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