Author: Bergh, 1877

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 90 mm

Sightings: Sunshine Coast

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Chromodoris annae Bergh, 1877

This species presents with the generalised classic Chromodoris colours and patterning but with a particular distinctive feature – a reticulated central dorsum that appears like small black specks spread across the blue coloured region.

Chromodoris annae is elongate oval in shape with the tail of the foot protruding posteriorly from beneath the mantle, otherwise the mantle completely overhangs the body and foot, though not excessively so.

The central region of the mantle is a mid to dark blue in colour carrying what appear to be numerous black specks, however closer observation reveals those to be fine punctations that lack pigment. It lacks a mid-dorsal longitudinal black band, possessed by many of its fellow Chromodoris, but exhibits a short black dash on the midline anteriorly between the rhinophores with some specimens having another short dash centrally. The blue reticulate region is encircled by a broad black band sometimes incomplete anteriorly but broader halfway along the body such that it pinches in the blue region. Outside of the black band is a white band and then a pale orange/yellow submarginal band completed by a thin white marginal border.

The rhinophores are orange, darker than the orange/yellow on the rhinophore pocket rims and the orange/yellow of the submarginal band. The gills are similarly coloured to the rhinophores but the raised gill pocket lacks colouration to the rim. The up to ten, simple gills form a horseshoe shape around the anus, being open posteriorly.

The sides of the body, dorsal foot and tail are blue. A black band runs medially down each side of the body but usually they do not meet posteriorly on the tail. A white band is outside the black with an orange/yellow marginal band.

Like all the Chromodorididae family members (indeed like all the cryptobranchs) Chromodoris annae is a spongivore. Most reports have it feeding upon Thorectidae sponges including Petrosaspongia sp. Chromodoris annae possesses defensive mantle glands, around the mantle edge, that contain noxious compounds sequestered from their prey sponge and concentrated therein. The bright colouration and patterning that Chromodoris annae exhibits are considered to be aposematic (a warning signal) to potential predators. Additionally, it has been suggested that the presence of these toxic compounds can be detected by some predators, and the nudibranch rejected as a food source by those predators that cannot detect the visual warnings.

The spawn is laid as a tight flat spiral of up to four whorls. It is translucent cream to white in colour without extra-capsular yolk. The laying of a flat egg spiral is a feature of all the true Chromodoris species as defined by the molecular sequencing of the Chromodorididae family by Johnson & Gosliner, 2012.

Distribution is widespread in the Indo-Pacific.

An interesting behaviour by this species was observed and documented by Willan, 2010, where two specimens acted in an aggressive manner towards each other, circling, rearing up and biting, such that sections of their mantle borders were damaged. No specific conclusions were drawn for the behaviour with mating, territorial and food competition being rejected as causes – interesting but inconclusive.

Previously there has been much confusion in the literature between Chromodoris annae and Chromodoris elisabethina, even by the original author of both these species, Bergh, 1877. A discussion of that confusion and its resolution can be followed in the paper by Rudman, 1982, wherein he also redescribed the species. There is now no doubt that Chromodoris annae is a good species, distinct from Chromodoris elisabethina.

David A Mullins – September 2022

References:
– Bergh, R. (1877). Malacologische Untersuchunger 11. In C. Semper (Ed.),Reisen im Archipel Philippinen. Wissenschaftliche Resulate.2 (2): 429-546, pls 51 57.

– Bergh, R. (1890). Malacologische Untersuchungen 17. Die Nudibranchien des Sunda-Meeres. In C. Semper (Ed.). Reisen im Archipel Philippinen. Wissenschaftliche Resultate, 2 (3): 873-991, pls 85 89.

– Bergh, R. (1905). Die Opisthobranchiata der Siboga Expedition. Siboga Expeditie Report, 50: 1 248.

– 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., (1999, November 19). Chromodoris annae Bergh, 1877. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/chroanna and associated messages.

– Rudman, W. B., Bergquist, P. R. (2007). A review of feeding specificity in the sponge-feeding Chromodorididae (Nudibranchia: Mollusca). Molluscan Research, 27(2): 60-88.

– Willan, R. C. (2010). Intraspecific aggression in the nudibranch Chromodoris annae Bergh, 1877: novel ‘fighting’ behaviour for the Chromodorididae (Gastropoda, Opisthobranchia). Basteria 74 (4-6): 89-94.

– 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.

– Cheney, K. L., White, A., Mudianta, I. W., Winters, A. E., Quezada, M., Capon, R. J., et al.(2016). Choose Your Weaponry: Selective Storage of a Single Toxic Compound, Latrunculin A, by Closely Related Nudibranch Molluscs. PLoS ONE 11(1): e0145134. doi:10.1371/journal.pone.0145134

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