DIVE LOG DECEMBER 25 ISSUE 415

Caryophyllidia Caryophyllidia are specialised low tubercle structures of the some of the Discodorididae family of nudibranchs. These are borne on the mantle dorsum. They consist of an apical, knob like, cilia–carrying sensory organ surrounded by a ring or crown of erect spicules all covered by a thin layer of epidermis. Although thought to serve primarily in a sensory capacity their true function has not yet been ascertained. Because of their spiculose nature however there is no doubt that they also serve to make the nudibranch disagreeable to predators especially so in those where the dorsum is almost completely covered by them. Shielding and decoy processes Shielding and decoy processes are possessed by a number of sea slug types including some of the true nudibranchs that have exposed gills and rhinophores.

own methods of overcoming them. Against the shell, stronger claws for external crushing, gizzard plates for internal digestive grinding or a combination of mechanical rasping and acid secretions to bore a hole through the shell into the softer tissue are examples. This is not to say the shell is useless for the shelled molluscs have proven to be a resilient and successful group. Some molluscan shells have developed quite elaborate forms in the attempt to counteract predator advances. Spicules Spicules embedded in the flesh together with tough, stiffened bodies while not as robust a shield as a calcareous shell, do serve to make the actual ultimate goal of the predator, the exposed flesh of the prey, unpalatable. In some species the spicules are not arranged in any particular formation however in some they protrude from the dorsum on tubercles.

Above: Tough or spiculose bodies. Clockwise from Top Left: Halgerda batangas has a tough ridged body. Phyllidiopsis cardinalis has a tough pustulose body. Atagema ornata has unpalatable caryophyllidia on its dorsum. A close-up of the caryophyllidia of Jorunna funebris .

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DIVE LOG Australasia #415 December ‘25

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