Spirula

Spirula, commonly known as the ram's horn squid or little posthorn squid, is a small, deep-sea cephalopod mollusk belonging to the order Spirulida. It is the only extant species in its order, family Spirulidae, and genus Spirula.

Description:

Spirula is characterized by its small size, typically reaching a mantle length of only a few centimeters. The most notable feature of Spirula is its internal, chambered, planispiral shell, which is typically white and iridescent. This shell, unlike the shells of nautilus or ammonites, is located internally within the mantle near the rear of the animal. The shell is buoyant and helps the squid maintain neutral buoyancy in the deep sea. The body is short and stubby, with eight arms and two tentacles. It has photophores, light-producing organs, located on its body, believed to be used for camouflage and communication.

Habitat and Distribution:

Spirula inhabits the deep ocean, typically found at depths between 100 and 1,750 meters. It has a circumglobal distribution, occurring in tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans. Because they live at great depths, Spirula are rarely observed alive. Empty shells are commonly found washed ashore on beaches, providing evidence of their presence in the area.

Behavior:

Spirula are believed to be vertical migrators, moving to shallower waters at night to feed and returning to deeper waters during the day. Their diet consists of small crustaceans and other planktonic organisms. Little is known about their reproductive behavior.

Taxonomy:

Spirula is classified within the class Cephalopoda. Its phylogenetic relationships with other cephalopods are not fully resolved, but it is considered to be a relatively ancient lineage. The order Spirulida was once more diverse, but Spirula spirula is the only surviving species.