Ecology
Platydoris scabra are considered part of the cryptic community on Heron Island reef. Platydoris scabra are well camouflaged, so although adults are present on the reef throughout the year, they are only occasionally found (Marshall & Willan 1999). This cryptic community is comprised of an enormous diversity of invertebrates including various colourful sponges and ascidians. Platydoris scabra are generally found at the reef crest under coral slabs and boulders, in close proximity to sponges (Marshall & Willan 1999). Nudibranchs within the genus Platydoris are often observed to co-occur with sponges as they are their preferred food source (Megina et al. 2002).
The loss of a hard, protective shell in nudibranchs is believed to have been compensated for by various adaptations including camouflage and the production of chemical defences (reviewed by Thompson (1960)). The sandy colouration of Platydoris scabra enables it to have excellent camouflage within its environment. Platydoris scabra is also heavily spiculated, making it distasteful to predators (Thompson & Brown 1984). The production of chemical defences in Platydoris scabra is therefore likely deemed unnecessary due to their cryptic colouration and skeletal defence. However, dorid nudibranchs are well known for producing secondary metabolites to deter predators (Faulkner & Ghiselin 1983). It is believed that some nudibranchs can obtain secondary metabolites and pigments from associations with sponges, and this enables them to more effectively camoflauge with their preferred food source and deter predators (Anderson 1971). Therefore it is possible that Platydoris scabra may favour habitats with sponges to better defend themselves against predations. Investigating whether, Platydoris scabra obtains secondary metabolites and pigments from sponges, as observed in other dorid nudibranchs, would be an exciting area for future research.
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Platydoris scabra crawling over piece of coral rubble (A) and Platydoris scabra residing under an overturned piece of coral rubble with a diverse community of brightly coloured invertebrates (B).
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Two photographs demonstrating the cryptic nature of Platydoris scabra: (A) crawling over coral rubble and sand and (B) hiding in a crevice beneath a piece of coral rubble.
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