Spirula spirula aka ram's horn squid. Probably my favorite cephalopod. A disappointing number of pictures available to reference, considering it has an important evolutionary relic - an internal spiral shell. It also has a yellowish-green photophore at the end of its mantle and a vertical-oriented swimming style. The juveniles are able to withdraw their head and arms entirely into their mantle when startled. The adult is not much bigger than your thumb, and its shell is found on beaches all over the world.