DIVE LOG DECEMBER 25 ISSUE 415

STAYIN ALIVE THE DEFENCES OF SEA SLUGS - Part 5 Passive Defences continued

Structural - Physical anatomical structures

retained the shell, or a reduced structure, or even just an external or internal remnant. This serves to cover and protect the vital viscera. Across all the sea slugs there are representations of the various degrees of that shell reduction or loss. The shell as a form of defence is self-evident. It is a hard structure into which the animal can withdraw for protection. However, as with all methods of defence, predators will, over time, evolve their

Shells Shells are probably the most recognizable feature associated with molluscs in general. While all of the many forms of the true nudibranchs lack a shell as an adult, having discarded the larval shell at metamorphosis, many of the sea slugs of the lower orders have

Above: Shells or remnants. Clockwise from Top Left: Bullina lineata has a bulbous shell into which the whole animal can withdraw. The thin fragile shell of Lobiger viridis covers the viscera of the animal like a cap but it cannot withdraw into it. Tylodina corticalis carries a flattened limpet-like shell that only provides overhead protection. This specimen of Tomoberthella martensi has autotomised its three sacrificial lobes and the gill is exposed but the thin internal shell is visible covering the viscera. DIVE LOG Australasia #415 -December ‘25 20 www.divelog.net.au