Ram's Horn Squid

Ram’s Horn Squid is the only living species for this order and family. The common name for this squid is derived from their internal coiled shell which is frequently washed ashore on tropical and subtropical coasts.

Identification

Similarly to nautiluses, S. spirula possesses an internal chambered shell which helps to control the animals’ buoyancy. The shell is an open coil, the edge of which is just visible in the animal. They are a short, cylindrical squid that is easily recognised by their coiled internal shell, light organ and fins on the end of the body. Their luminescent skin is a dark reddish brown, however this colouring is often lost in trawled animals. This species has no toothed tongue (radula) like many other cephalopod species.

Habitat

This mesopelagic small squid lives in mid-water depths of the open ocean. They are typically associated with oceanic islands or continental land masses near deep water. They are thought to be a schooling squid and can be very abundant.

Distribution

Found throughout the tropical Atlantic and Indo-West Pacific Region.

Other behaviours and adaptations

Live animals are rarely seen, however they have been observed to retract their head and arms into their mantle, closing the opening with the two pointed flaps above and below the head. When at rest this species maintains a vertical position, head downwards.

During the day S. spirula rests at around 550-1000m depth, rising at night to feed at around 100-300m. The function of their light organ is unknown, as unusually it aims upwards, the opposite of most midwater animals which produce light from below to cancel their silhouette.

Life history cycle

S. spirula is thought to live for around 18-20 months, achieving sexual maturity at 12-15 months.

Breeding behaviours

Young animals have been collected at depths of 1000-1750m, suggesting that females probably lay eggs at the bottom of the continental slope. Amazingly, at these depths the pressure on the egg shell would be more than half a tonne!

References

• Jereb, P., & C.F.E Roper (eds) (2005) Cephalopods of the World: Chambered Nautiluses and Sepioids, Food & Agriculture Organization of the United Nations Catalogue for Fishery Purposes, Rome, No. 4, Vol. 1
• Norman, M., (2000) Cephalopods- A World Guide, ConchBooks, Germany (Hackenheim)
• Norman, M & A. Reid., (2000) A Guide to Squid, Cuttlefish and Octopuses of Australasia, CSIRO Publishing, Victoria (Collingwood)