Thuridilla lineolata

Description:

This is not a nudibranch, but it belongs to the same class (Gastropoda) as nudibranchs. Like nudibranchs, however, this sea slug has evolved out of its shell and uses bright colors to warn predators off. This species might be confused with its cousin, Thuridilla gracilis, due to similar coloration and patterns. T. lineolata grows bigger and does not "nod" its head when crawling, a behavior that T. gracilis is known for. All species of this genus eat algae.

Notes:

This slug was in about 28m of water at a dive site called Marissa 1, off the western coast of Samal Island, Philippines. It measured about 2.5cm long and was crawling across the rubble in a fairly fast pace.