Author: (Pease, 1860)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 20 mm

Sightings: Sunshine Coast

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Goniobranchus decorus has gone through several name changes over the years.

Doris decora -> Glossodoris decora -> Chromodoris decora -> Goniobranchus decorus

Pease first described this nudibranch from Hawaii as Doris decora in 1860 but did not include an illustration. His description however contained the following: “…. a medial whitish longitudinal strip which is bifurcated posteriorly and dotted with purple.”

Bergh in 1880 published an illustration of a nudibranch recognising the name that Pease gave it earlier and which clearly showed the features described.

In 1938 Baba described a similar animal but although it did have a white forked medial line, that line did not bear the purple spots. He named his animal Glossodoris setoensis.

In a little known paper Allan, J., 1947 stated under the heading of Glossodoris decora (Pease), 1860: “….leaves little doubt that G. setoensis, Baba is a synonym of it.”

Later again, in 1953, Baba recognised Allan’s conclusion and in a revised list of Glossodoris species, published:
Glossodoris decora (Pease, 1860) = G. setoensis (Baba, 1938). (See Allan, 1947).

So the original author of setoensis himself, also synonymized it with decora.

Rudman, 1986 also states: “….G. setoensis should be considered a junior synonym of C. decora.”

Marshall & Willan, 1999, also list Glossodoris setoensis as a synonym.

Nudibranch & Sea Slug Identification – Indo-Pacific 2nd edition (NSSI ii) does show both variations but with the caveat: “Additional work is necessary to determine whether these are colour variants or distinct species.” In other words they do not know, until molecular sequencing is undertaken.

In Johnson & Gosliner, 2012, Goniobranchus setoensis was not sequenced but only included as a hypothesized member.

We have decided to remain with Goniobranchus decorus until such time as that additional work is undertaken.

David A. Mullins – January 2023

References:
– Pease, W. H. (1860). Descriptions of new species of mollusca from the Sandwich Islands. Proceedings of the Zoological Society of London, 28: 18-37.

– Bergh, L. S. R. (1880). Malacologische Untersuchungen 1 (Supplement 1). In C. Semper (Ed.), Reisen im Archipel Philippinen, Wissenschaftliche Resultate, 2(4): 1-78, pls A-F.

– Baba, K. (1938). Opisthobranchia of Kii, Middle Japan. Journal of the Department of Agriculture, Kyushu Imperial University, 6: 1-19.

– Allan, J. (1947). Nudibranchia from the Clarence River Heads, north coast, New South Wales. Records of the Australian Museum, 21: 433-463, pls 41-43.

– Baba, K. (1953). Three new species and two new records of the genus Glossodoris from Japan. Publications of the Seto Marine Biological Laboratory, 3: 205-211.

– Rudman, W. B. (1986). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Noumea purpurea and Chromodoris decora colour groups. Zoological Journal of the Linnean Society 86(4): 309-353.

– Marshall, J. G. & Willan, R. C. (1999). Nudibranchs of Heron Island, Great Barrier Reef: A survey of the Opisthobranchia (sea slugs) of Heron and Wistari Reefs; Backhuys: Leiden, The Netherlands, 1999.

– 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.

– Gosliner, T. M., Valdés, Á., Behrens, D. W. (2018). Nudibranch and Sea Slug Identification: Indo-Pacific – 2nd Ed. New World Publications, Jacksonville, Florida.