DIVE LOG DECEMBER 25 ISSUE 415

The phanerobranchs especially, those nudibranchs that cannot retract their gill for preservation, have fleshy processes around or in proximity to the gill that act in a protective role. As well as providing a form of physical barrier they could also be serving in a decoy function by having a resemblance to, or an even more attractive appearance to the indispensable organs they seek to safeguard. The rhinophores of some are protected in a similar manner. Among the cryptobranch nudibranchs, the Ceratosoma and Miamira are unique in possessing protective gill structures even though the gills are able to be totally withdrawn.

As we will see in the chemical defences section, the flesh of many of these structures are taken a step further by incorporating distasteful/noxious substances that may deter a predator from taking a bite but certainly from taking a second bite. With regard to the aeolids with their non-retractable rhinophores, it might be the case that these are lost to the sight of a predator amongst a virtual sea of waving cerata. A primary purpose therefore of many of these extra-rhinophoral and extra-branchial structures could be considered sacrificial in order that the vital parts – the rhinophores and gills, are left in working order following a strike by a predator. Next issue: Chemical Defences

Above: Shielding/decoy processes. Clockwise from Top Left: Bornella anguilla has processes that protect the rhinophores and fine gills and even brightly coloured to act as decoys. The massive sturdy lobe of Aegires serenae protects the gills. Trapania tora has extrarhinophoral and extrabranchial processes that look more inviting that those they protect, as do all the Trapania . The giant posterior horn of Ceratosoma tenue protects the gills even though it can still retract.

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DIVE LOG Australasia #415 -December ‘25

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