Spirula spirula is a
species of deep-water
squid-like
cephalopod mollusk. It is the only
extant member of the
genus Spirula, the
family Spirulidae, and the
order Spirulida. Because of the shape of its internal shell, it is commonly known as the
ram's horn squid or the
little post horn squid. Because the live animal has a light-emitting organ, it is also sometimes known as the
tail-light squid.