This fantastic species is a type of pleurobranch, a close cousin to the more famous nudibranch sea slugs. The Euseleonops luniceps, also known as the Moon-Headed Sidegill slug is a type of pleurobranch. This is a very seasonal species in Sydney and can usually be seen between October and December only and nearly always at night. They look like a mix of an octopus and a slug. The first time I saw one I was mesmorised and to be honest I am still whenever I see one.