Arminid Nudibranch
Janolus sp.
Nudibranchs have shells as larva, but shed them when they mature. Shells are heavy and make moving around difficult. Most molluscs use the shell as a primary defence, but nudibranchs have developed other techniques for protection, such as toxic secretion. A few make their own poisons, but most utilize the toxic metabolites from what they eat.
Anilao, The Philippines