29th Dec 2015 - Environment
The Spirula Shell
Nature produces the most beautiful forms and patterns. The shell of Spirula spirula, or the Ram’s Horn Squid, is one such example.
These beautiful open-coiled shells are the buoyancy organ of a species of small squid-like cephalopod that measures only around 45 mm in length, and which is the only non-extinct member of its taxonomic order, family and genus. The Spirula is found in the deep waters of tropical and sub-tropical seas throughout the Atlantic and Indo-West-Pacific regions, spending the daylight hours at depths of between 500 and 1000 metres before rising at night to feed at between 100-300 metres; a pattern of diel vertical migration that constitutes the largest migration of biomass in the world. It has a light-emitting organ in the upward-pointing tail, the reason for which is unknown as this feature in other similar organisms usually points down to help cancel out the creature’s silhouette. The spirula’s chambered shell is used to control buoyancy and keep it oriented in a head-down position, and because it is light-weight and durable the shells of dead spirula are often carried in oceanic currents before being washed ashore on beaches as far apart as the Canary Islands and New Zealand, often in great numbers.
As sightings of live specimens are extremely rare, the beautiful shell of Spirula spirula is the only evidence of its existence that most of us will ever see; curious white coils littering the high tide lines of lucky beaches. If you’ve ever seen them and paused to pick one up and turned it over in your hands whilst wondering what kind of creature created or lived in it, then we hope that now you know a little more about just one of the fascinating species that inhabit our oceans.