Author: (Rudman, 1985)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 70 mm

Sightings: Sunshine Coast

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Ardeadoris averni (Rudman, 1985)

Ardeadoris averni is a large elongate-oval shaped dorid nudibranch recorded up to 70 mm in length. There is a broad mantle overlap and the mantle edge presents with many folds, usually with a large distinctive infold each side at the midway mark of the mantle. The edge of the mantle is thick giving a “puffy” look when combined with all the folds. The tail of the foot is visible where it extends past the posterior edge of the mantle. The rhinophores can retract into protective pockets. The gills too can retract into a protective pocket. The gill is large and arranged in an arc around the anus, open posteriorly, with each end of the arc forming an inward spiral. The gills move continuously with a regular rhythmical motion when expanded.

The mantle colour is a semi-translucent white with a thick red-orange margin both dorsally and ventrally. There is also a sub-marginal band of vivid opaque white that contain underlying mantle glands, according to Rudman. The margin of the foot/tail carries a narrower band often of a lighter colour to that of the mantle margin. The coloured band to the foot/tail margin is considered diagnostic in separating this species from otherwise similarly-coloured species. (In other words, should be present to confirm this species – sometimes there is just a hint of the orange.) The rhinophore clubs are orange/brown and bear white lines up both the anterior and posterior faces. The colour of the clubs tapers off to translucent white stalks. The gills have a white core but with brown edging and light brown to both inner and outer faces.

Ardeadoris averni is a spongivore but the type of sponge preyed upon has not been identified/recorded.

The spawn of Ardeadoris averni is laid as an upright yellow coil apparently without extra-capsular yolk.

Distribution is broadly the western Pacific, from Japan in the north down through the Philippines, Malaysia, Indonesia, PNG, Solomon Islands, the GBR to central NSW.

Originally described as: Glossodoris averni.

Later, in a wide ranging molecular sequencing of the Chromodorididae family in 2012 (Johnson & Gosliner), it was shifted to Ardeadoris, a genus raised by Rudman in 1984. It joined Ardeadoris egretta (Rudman’s type species for the genus) and Ardeadoris scottjohnsoni, but going across with it were ten other species all from the Glossodoris genus (and one from Noumea). This group of ten were known by taxonomists to be similar in some respects but at the same time to be varying in certain aspects from the other Glossodoris making them difficult to place definitively. This was resolved by that molecular sequencing. There are a number of species in the Chromodorididae family, and across several genera, that have a substantially white mantle trimmed with a yellow/orange line to the mantle margin or sub-margin. Nearly all of the current thirteen Ardeadoris species fall into that general description. The phylogram in Johnson & Gosliner’s 2012 paper shows Ardeadoris averni to be most closely related to A. angustolutea followed by A. scottjohnsoni and A. egretta.

The species was named by Rudman: “….after my research assistant Mr. G. Avern….”

Above: Ardeadoris averni

David A. Mullins – February 2022

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, (1990.) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: further species of Glossodoris, Thorunna and the Chromodoris aureomarginata colour group. Zoological Journal of the Linnean Society, 100(3): 263-326.

– Rudman, W. B., (December 1, 1998). Glossodoris averni Rudman, 1985. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/glosaver and associated messages.

– 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.

– Debelius, H. & Kuiter, R. H., (2007). Nudibranchs of the World. IKAN-Unterwasserarchiv, Frankfurt.

– Coleman, N., (2008). Nudibranchs Encyclopedia. Neville Coleman’s Underwater Geographic Pty Ltd, Springwood, Qld.

– 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.

– Nimbs, M. J. & Smith, S. D. A., (2017). An illustrated inventory of the sea slugs of New South Wales, Australia (Gastropoda: Heterobranchia). Proceedings of the Royal Society of Victoria 128: 44-113.

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