No bones about it

August 14th 2018

You have possibly heard about cuttlefish and their bones. If you’ve ever had a pet caged bird for example you are very likely to have given it a calcium-rich dietary supplement in the form of a piece of cuttlebone.

The cuttlebone is a chambered, gas-filled internal ‘shell’ which cuttlefish use for buoyancy control.

Cuttlefish, being marine molluscs, are related to snails, etc. and form part of a group known as cephalopods, which means ‘head foot’. All the species in the group have tentacles attached to their head! The largest species of cuttlefish in british waters is the Common Cuttlefish, Sepia officinalis which can grow to a length of about 45cm. The largest species worldwide is the Australian Giant Cuttlefish, Sepia apama and it can exceed one metre in length.

On 24thJuly 2018 Avril and I accompanied about 18 other folk on the Highlife Highland Ranger’s Rock-pooling day at Clashnessie. It’s always a great day out, not sure if the kids or adults have most fun!

I decided to have a go at ‘push-netting’ to see what I could come up with. This involved pushing a small net, mounted on a wooden frame, through the sandy bottom of the shallow sea water. The first push drew a blank, the second push however delivered the ‘catch’ of the day, and a first for everyone there, – a Common Bobtail Cuttlefish, Sepietta oweniana.

After some reading up we found out that although these small animals are closely related to true cuttlefish they in fact have no cuttlebone! This one was an adult and measured c45mm in length, excluding the tentacles.

There are very few records of adults of this species around the coast of Assynt and this one was clearly not happy at being caught. Shortly after we placed it in a plastic tray it produced two clouds of ink, this is a defence mechanism. This ink was, at one time, used by artists and writers, hence the colour sepia. Sepia is reddish-brown and gets it’s name from the rich brown pigment derived from the ink sac of cuttlefish, Sepia spp.

Not that our specimen was simply ‘sepia’ it did give the distinct impression at one point of trying to change its colour to match the small amount of sand in the corner of the tray.

David Haines

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