Promoting Intertidal Sciences blog | Dr Mike Kent | Dec 4th 2018

The Blue-Rayed limpet, Patella pellucida:

A marine creature that would not look out of place on a Christmas Tree.


On a bleak midwinter’s day, scrambling wet and bedraggled, knee-deep in seaweeds, I came across a marine creature which would not look out of place on a Christmas tree. It is the tiny Blue-Rayed limpet, Patella pellucida. Rarely exceeding 2cm long, it lives and feeds on the blades or fronds of serrated wrack and in the holdfasts of kelp on the wave-swept shores of Polzeath.

Exquisitely adorned with dashes of iridescent blue-green rays, this limpet is an absolute delight to behold. I’ve long-admired the limpet’s beauty, but have given little thought to the function of the kingfisher-coloured rays, thinking that they are probably the by-product of some metabolic process. However, recent research has revealed that the rays are the result of an interaction between two highly organized mineralized structures. These ensure that the vivid shine of the blue-green stripes can be seen underwater from a wide range of viewing angles. The complexity of the optical arrangement of the structures suggests that the rays have a function beyond being mere by-products of metabolism. The researchers speculate that the rays have evolved to protect the limpet by mimicking the colours of toxic or otherwise distasteful organisms, such as Polycera elegans, a distinctive colourful but distasteful sea slug which has a smooth orange body speckled with brilliant blue blotches.

Shells of the Blue-Ray limpet may be too small to put on a tree but, much like twinkling tinsel and sparkling baubles, they can bring colour and light to an otherwise dull December day. And like Christmas decorations for Christians, seeing them during advent can symbolize the coming of our Lord, He who is the true Light:

All things came into being through him,

and without him not one thing came into being.

What has come into being in him was life,

and the life was the light of of all people.

The light shines in the darkness,

and the darkness did not overcome it.  

John 1:3-5