Author: (Burn, 1958)

Order: Nudibranchia  Family: Onchidorididae

Maximum Size: 8 mm

Sightings: Sunshine Coast

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Idaliadoris maugeansis (Burn, 1958)

This species was originally described by Robert Burn in 1958 from Victorian specimens (type locality Torquay, outside Port Phillip Heads, Victoria, Australia). The distribution is known to extend as far south as Southern Tasmania. To find them up in subtropical Queensland is quite a range extension. It is placed in the family Onchidorididae based on radula morphology and the nature of the buccal pump. Onchidorididae itself is placed in the superfamily Onchidoridoidea, a suctorian group, that also includes Goniodorididae amongst others.

Idaliadoris maugeansis is a small flat dorid species of phanerobranch nudibranch. Broadly ovate in shape it reaches 8 mm in length. The mantle is wide, completely covering the foot, the edges resting upon the substrate. Embedded in the flesh of the mantle are conspicuous closely packed glass-like spicules that stiffen the mantle and most likely serve to render the animal unpalatable. Where the mantle extends past the body proper its translucency allows the nature of the substrate, most often its prey of encrusting bryozoans, to show through making it remarkably cryptic in that situation. Tall tapering and cylindrical translucent papillae completely crowd the notum. The shape of these dorsal papillae are diagnostic for the genus Idaliadoris. The background colour is creamy white with yellow/orange spots and patches. The rhinophores are tall tapered and translucent with conspicuous lamellae. The gill is arranged as a circle of branchiae around the anus. These are non-retractile but can contract to a degree. Each of the branchiae is separate and situated in its own individual pocket. This circle of gill branchiae surrounds a small section of the dorsum that also carries the aforementioned papillae. The oral veil is extremely large extending past and curving around the margins of the foot in a semicircular manner.

The spawn is laid as a flat spiral of five to seven whorls upon the substrate. The egg capsules are conspicuous in the spawn and may range in colour from white to pale yellow/orange. This is a good species, separate from Idaliadoris depressa with one of the observable characteristics separating it from I. depressa being the single row of eggs in the spiral rather than the double of I. depressa. (R. Burn, personal communication) The larvae are lecithotrophic in development. The structure of the egg mass too, is diagnostic for the genus Idaliadoris.

Normally found on the underside of rocks in shallow depths feeding on encrusting bryozoans, their presence often betrayed by the spiral spawn they lay.

Previously known as Onchidoris maugeansis. This species was placed in a new genus Knoutsodonta by Hallas and Gosliner in 2015 and confirmed by Furfaro & Trainito in 2017 based on the lack of a rachidian (central) tooth in the radula and supported by related molecular data.

A later paper (Ortea, J., 2021).  synonymised Knoutsodonta with Atalodoris.

The most recent paper (Furfaro et al, 2022) separated 8 species out of Atalodoris into Idaliadoris.

Originally described as Lamellidoris maugeansis.
Previously known on this site as Knoutsodonta maugeansis. (Changed May 2022)
Previously known on this site as Atalodoris maugeansis. (Changed February 2023)

David A. Mullins – June 2020 (Revised February 2023)

References:
– Burn, R. (1958). Further Victorian Opisthobranchia. Journal of the Malacological Society of Australia Vol. 1 (2): 20-36.

– Millen, S. V. (1985). The nudibranch genera Onchidoris and Diaphorodoris (Mollusca, Opithbranchia) in the northeastern Pacific. Veliger 28, 80–93.

– Rudman, W. B., (1998). Family Onchidorididae P. 992 in Beesley, P. L., Ross, G. J. B. & Wells, A. (Eds) Mollusca: The Southern Synthesis. Fauna of Australia. Vol.5 CSIRO Publishing, Melbourne, Part B 565-1234 pp.

– Burn, R. (2006). A checklist and bibliography of the Opisthobranchia (Mollusca: Gastropoda) of Victoria and the Bass Strait area, south-eastern Australia. Museum Victoria Science Reports 10: 1-42.

– Burn, R. (2015). Nudibranchs and related molluscs. Museum Victoria.

– Hallas, J. M. & Gosliner, T. M. (2015). Family matters: The first molecular phylogeny of the Onchidorididae Gray, 1827 (Mollusca, Gastropoda, Nudibranchia). Molecular Phylogenetics and Evolution. 88: 16-27.

– Furfaro, G. & Trainito, E. (2017). A new species from the Mediterranean Sea and North-Eastern Atlantic Ocean: Knoutsodonta pictoni n. sp. (Gastropoda Heterobranchia Nudibranchia). Biodiversity Journal. 8(2): 725-738

– Hallas, J. M., Chichvarkhin, A., & Gosliner, T. M. (2017). Aligning evidence: concerns regarding multiple sequence alignments in estimating the phylogeny of the Nudibranchia suborder Doridina. Royal Society open science. 4: 171095.

– Ortea, J. (2021). Nueva especie del género Atalodoris Iredale & O’Donoghue, 1923 (Mollusca: Nudibranchia) colectada en la Concha de Artedo, Asturias, dedicada al periodista deportivo José María García. Revista de la Academia Canaria de Ciencias. 33: 97-106.

– Furfaro, G., Trainito, E., Fantin, M., D’Elia, M., Madrenas, E. & Mariottini, P. (2022). Mediterranean Matters: Revision of the Family Onchidorididae (Mollusca, Nudibranchia) with the Description of a New Genus and a New Species. Diversity 2023, 15, 38.