Author: (Rudman, 1990)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 45 mm

Sightings: Sunshine Coast

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Ardeadoris symmetrica (Rudman, 1990)

Ardeadoris symmetrica is a medium-sized dorid nudibranch reported up to 45 mm in length. The mantle is oval in shape with a wide overhang of the foot. The mantle margin is thrown into a series of folds often with a distinctive large fold each side about halfway along. The very edge has a thick look about it. The tail of the foot is visible where it protrudes beyond the posterior margin of the mantle. The rhinophores can retract into protective pockets. The gills too can retract into a protective pocket. The gill is arranged in an arc around the anus, open posteriorly, with each end of the arc forming an inward spiral. Each gill is more inflated than those of Ardeadoris egretta. The gills move continuously with a regular rhythmical motion when expanded.

The base colour of the mantle is translucent white but that white may be quite muted. Overlaying the translucent background is a broad muted opaque white band running medially from anterior to the rhinophores back behind the gills. It presents as an irregular shape but is mostly symmetrical about the midline. It may present as separate anterior and posterior portions. The very edge of the mantle carries a red or red-orange line. At times the red appears to “bleed” into the white causing the edge to be indistinct. The coloured line on the mantle margin of this species is the thinnest of all the described species of Ardeadoris. Just inside this red line is a broad opaque white band. The foot and tail of the foot carry an opaque white border. The midline of the tail may carry an opaque white line. The rhinophores, stalk and club, are translucent/watery red-orange with a red line running up both anterior and posterior faces. The gills are translucent white with red-orange edging.

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

Distribution is very broad Indo-West Pacific from Japan in the north down through the Marshall Islands, Philippines, Malaysia, Indonesia, PNG, Solomon Islands, New Caledonia the GBR to southern Queensland, Australia and across the Indian Ocean to Reunion Island, South Africa, Mozambique and the Red Sea.

Originally described as: Glossodoris symmetricus.

Later, in a wide ranging molecular sequencing of the Chromodorididae family in 2012 (Johnson & Gosliner), it was shifted to Ardeadoris, (by hypothesis), 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.

Regarding the naming of this species, Rudman advises: “The name G. symmetricus is a reference to the symmetrical white patch or patches down the midline of the mantle.”

David A. Mullins – February 2022

References:
– 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., (April 25, 2000). Glossodoris symmetricus Rudman, 1990. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/glossymm and associated messages.

– Nakano, R., (2004). Opisthobranchs of Japan Islands. Rutles, Inc.

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

– Yonow, N. (2008). Sea Slugs of the Red Sea. Pensoft Publishers.

– 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.

– Tibirica, Y., Pola, M. & Cervera, J. L., (2017). Astonishing diversity revealed: an annotated and illustrated inventory of Nudipleura (Gastropoda: Heterobranchia) from Mozambique. Zootaxa 4359 (1): 001–133

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