20th July 2018
Established 1872. Online since 1996.

Looking for chitons, cousin to the limpet

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A STEADY trickle of migrants continued to pass through the North Isles last week.

Mostly they were the usual suspects but a barred warbler was at Norwick on the 18th, a whinchat at North Dale, Unst, on the 20th, while a stonechat and red-backed shrike both graced Whalsay the following day. Three sand martins passed through Skerries on the 18th as they moved south.

There’s something really ex­citing about hearing the teu-teu-teu of a greenshank as it flies round, this time at Burrafirth on the 19th. Other waders moving through the North Isles included ruff, black-tailed godwits and common sandpiper.

One aspect of wildlife that gets much less than its fair share of attention is intertidal wildlife – those creatures that inhabit areas between the tides, particularly on rocky shores. But a closer look will reveal its fascinations. One such place is below the shore station at Burrafirth, where I had a good look recently.

At first sight the pools appeared full of edible winkles but as I watched, a couple of shells started moving rather more speedily than they should – a real giveaway that they had been commandeered by hermit crabs. With no permanent home of their own, hermit crabs are always on the lookout for empty shells. But as they grow by successive moults, so they need to upsize their “homes”.

If you happen to be there just at the right time you can occasionally encourage them to do this by strategically placing a suitable “des res” – a great way to gain the interest of young bairns. Vulnerable when exposed, they scuttle from one to the other for a “viewing” and if acceptable will install themselves in backwards, curling their bodies around the central column and closing up the entrance with their large front claw.

Many folk are familiar with limpets with their conical one-piece shells holding on “like limpets” to their made to measure place on the rock face when the tide goes out.

But preferring the darker undersides of rocks are altogether smaller relatives of limpets, the chitons. More aptly known as coat-of-mail shells, their shells are divided into eight segments.

Carefully lifting bits of rock out of the water briefly to see what is underneath is fine as long as you quickly replace it as found. This way I soon found one which promptly demonstrated the flexibility of its shell as it began moving away from the light.

With hungry creatures ever looking for a meal, these small, alga-grazing molluscs blend beautifully with their environment. What a treat to get a brief glimpse before the tide began flowing again.

Wendy Dickson