Spirula spirula in Cornish waters

CORNWALL

Spirula spirula in Cornish waters

Also know as little post horn.

Described as "peculiar", one would not easily guess that this small cephalopod is more closely related to cuttles than to the nautilus. It is sufficiently different from its nearest relatives to occupy its own family which it shares with no other species. When alive it hangs upside down in depths of water varying from 550 to 1,000 metres in day time and 100 to 300 metres at night. The chambers in the shell contain a gas which gives it buoyancy and allows it to vary the depth it inhabits. Its eight arms and two tentacles stretch into the water when it is hunting, but they can be completely drawn into the mantle. Two tiny fins allow it to orientate its way through the water by means of their fluttering movements, and a small organ at the posterior of the body is known to glow for hours at a time.

Spirula spirula - photograph by Roger Driver
Spirula spirula
photograph by Roger Driver

The photograph shows the shell of one of these animals, picked up on Perranporth Beach by Roger Driver in October 2000 and instantly recognized by Paul Gainey. This was a particularly large example at about an inch across, as they rarely exceed a half inch. Its common name, little post horn, is very apt as it describes the way it coils in a single plane, without the coils touching one another. The Germans use the same name (Pösthornchen), as do the French (Cornet de Postillon).

Stella Turk

Stranding notes

The animal is believed to be as short-lived as cuttlefishes, dying after one to two years. Also like cuttlefishes, the shells may be cast up in thousands on tropical shores. On European shores they are rare, and one is lucky to find one or two, and never with the remains of the animal. They are common off the West Indies, and Cornish shells may drift from there, borne on the North Atlantic Drift arm of the Gulf Stream, like so much else.