Author: (Quoy & Gaimard, 1832)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 90 mm

Sightings: Sunshine Coast

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Chromodoris magnifica (Quoy & Gaimard, 1832)

The Chromodoris genus, up until 2012, was the most speciose genus within the the most speciose family (Chromodorididae) across all of the sea slugs. The Chromodorididae review (Johnson and Gosliner, 2012) effectively gutted Chromodoris in the Indo-Pacific, transferring approximately two-thirds of the described genus members to Goniobranchus. Additionally all of the Eastern Pacific and Atlantic Chromodoris species were relocated into the provisional genus “Felimida”. Chromodoris now holds just the black-lined Indo-Pacific species (plus Chromodoris aspersa) that all lay a planar (flat) egg mass.

Magnificent by name and magnificent in appearance Chromodoris magnifica is a large cryptobranch species of nudibranch exhibiting colours and patterning that are similar to a number of closely related species. There is a very good reason for this similarity that will be explained below.

The primary colour of the broad mantle of Chromodoris magnifica is white, with a broad orange submarginal band, a narrow white margin and several broad longitudinal black bands in the central mantle region. There is variation exhibited in the presentation and arrangement of these central black bands but most usually there are three, a midline from in front of the rhinophores back to the gill pocket and a lateral on each side, again from in front of the rhinophores, sometimes joining anteriorly and then running back to behind the gill pocket and often also joining there too. Sometimes the three black bands are not so delineated as in the main image above, spreading out and leaving just a couple of thin white dashes, or conversely the black itself may be reduced to a series of dashes especially most centrally. Both gills and rhinophores are orange but of a darker hue than the submarginal mantle band. The rims to their pockets are also orange. The foot bears a broad orange marginal band and the sides of the body, concealed by the broad mantle overlap, except for the posterior-most portion of the foot, may have up to three black lines.

Chromodoris magnifica is most similar to Chromodoris africana and Chromodoris quadricolor however C. africana does not have a white mantle margin and C. quadricolor has a bluish tinge to the central dorsum. Both of these species though are considered to have a Red Sea, Indian Ocean distribution. There are at least 18 described species in the broad Indo-Pacific region that exhibit black longitudinal stripes on their mantle together with striking combinations and variations of white and/or blue and/or orange. These colours and patterns are a warning sign to potential predators, such as fish, that they have glands in the mantle making them distasteful or poisonous to eat. This advertising to potential predators is called aposematic colouration. The parallel development of these patterns by different species to share the load of “training” predators to avoid them is termed Mullerian mimicry.

Chromodoris magnifica preys upon sponges identified as Negombata sp. of the family Podospongiidae, and possibly others (e.g. Lamellodysidea). It obtains from that sponge a compound called Latrunculin A that is considered to be one of the most toxic compounds isolated from sponges. Interestingly the two species that most closely resemble Chromodoris magnifica in colour and pattern – C. africana and C. quadricolor – also feed upon the same sponge.

The spawn is white. There was some confusion regarding the actual shape of the spiral. It was reported as  upright crenulated (Klussman-Klob & Wägele, 2001) however it is now known to be planar (flat) (Wilson & Lee, 2005). Species of the revised genus Chromodoris are now known to all lay a planar egg spiral on the substrate. That 2005 paper by Wilson & Lee proved to be prescient regarding the eventual reorganisation of Chromodoris (Johnson & Gosliner, 2012) and hasn’t received the recognition it deserves outside of the narrow taxonomic community.

More recent molecular work on Chromodoris species has revealed “…… undocumented diversity, ultimately expanding our knowledge of species boundaries in this group, while also demonstrating the limitations of colour patterns for species identification in this genus.” (Layton, Gosliner & Wilson, 2018). Briefly, this research has shown (among other conclusions) that the colour patterns we rely upon so heavily for distinguishing species in colour photographs is questionable. For example Chromodoris joshi, quite distinctive in the Philippines, takes on (mimics) a C. magnifica look in Western Australia. Also C. magnifica collected at greater depths (mesophytic reefs) can have a very different appearance.

The distribution of Chromodoris magnifica is broadly Indo-Pacific, from Okinawa in Japan down to SE Queensland and the Western Australia coast, Australia.

Originally described as: Doris magnifica from a specimen collected in New Guinea during the voyage of L’Astrolabe.

Chromodoris magnifica is the type species of Chromodoris.

David A. Mullins – January 2021

References:

– Quoy, J. R. C. & Gaimard, J .P. (1832-1835). Voyage de découvertes de l’ Astrolabe exécuté par ordre du Roi, pendant les années 1826-1829, sous le commandement de M. J. Dumont d’Urville. Zoologie. 2 (1832): 270-272, Zoologie, Atlas (Mollusques) (1833): pl 20.

– Rudman, W . B. (1977). Chromodorid opisthohranch Mollusca from East Africa and the tropical West Pacilic. Zoological Journal of the Linnean Society. 61: 351-397.

– Rudman, W. B. (1982). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris quadricolor, C. lineolata and Hypselodoris nigrolineata colour groups. Zoological Journal of the Linnean Society. 76: 183-241.

– Rudman, W. B. (1984). The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: a review of the genera. Zoological Journal of the Linnean Society. 81(2): 115-273.

– Rudman, W. B. (1998, April 8) Chromodoris magnifica (Quoy & Gaimard, 1832). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/chrmag 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, 1999.

– Klussman-Kolb, A. & Wägele, H. (2001). On the fine structure of opisthobranch egg masses (Mollusca, Gastropoda). Zoologischer Anzeiger. 240, 101–118.

– Wilson, N.G. (2002) Egg Masses of Chromodorid Nudibranchs (Mollusca: Gastropoda: Opisthobranchia). Malacologia, 44(2): 289-305.

– Wilson, N. G. & Lee, M. S. Y. (2005) Molecular Phylogeny of Chromodoris (Mollusca: Nudibranchia) and the identification of a planar spawning clade. Molecular Phylogenetics and Evolution 36: 722–727.

– 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.

– Layton, K. S., Gosliner, T. M. & Wilson, N. G. (2018). Flexible colour patterns obscure identification and mimicry in Indo-Pacific Chromodoris nudibranchs (Gastropoda: Chromodorididae). Molecular Phylogenetics and Evolution 124: 27–36.

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #356 (March 2018): 12 by David A. Mullins.