I have been leading guided Seashore Safaris on the Gower coast, South Wales, every summer for the past eight years. During that time, I have encountered an array of fascinating marine creatures hiding in rockpools and gulleys, clinging to overhangs and nestling under boulders – including chitons.
Keen-eyed children and adults alike often enquire about the strange, tiny, woodlice-like ‘fossils’ they've spotted. These inconspicuous structures usually measure no more than 2cm in length and invariably turn out to be living animals called chitons.
What are chitons?
Chitons (pronounced ‘kite-ons’) are enigmatic and fascinating marine invertebrates. They are known from fossils dating back at least 300 million years, and have changed little with the passing of time.
Chitons belong to the phylum Mollusca (along with sea snails, sea slugs and bivalves), and are sometimes known as ‘coat-of-mail shells’, which alludes to their carapace of eight overlapping and interlocking plates that resemble the chain mail sported by knights of old. They have small heads, and a lack of tentacles and eyes means it’s not always obvious which end is which.
Where do chitons live?
Chitons occur only in marine habitats. There are about 600 species worldwide, 15 of which have been recorded from British coasts. Head out on a rockpool ramble and you may encounter the grey chiton Lepidochitona cinerea, our most common species, or perhaps Acanthochitona crinita, easily recognised by the 18 bristly tufts sprouting around its shell.
Chitons usually live alone or in small clusters of 3–4 on the undersides of rocks on the lower shore, or on the sides of rockpools on moderately exposed rocky shores. They are not always easy to spot, camouflaged as they are against their rocky backgrounds or obscured by mud or silt.
These are well-adapted little molluscs, perfectly equipped for life on the seashore. Like limpets, they cling to rocks using a strong, well-developed, muscular ‘foot’. The irregular surface of their rocky surroundings poses no problem, as their articulated bodies readily flex and bend, the foot contorting to the outline of even the most rugged surface.
If a chiton becomes detached from its habitat, it curls into a ball like a woodlouse – a manoeuvre enabled by its shell plates. This is a neat defensive strategy, protecting the animal from harm if it finds itself swept away by rough waves and dashed against the shore.
What do chitons eat?
These molluscs are herbivores, using their hard, rasping radular teeth to graze on small algae and micro-organisms. Some of these teeth are reinforced with iron and silicate compounds, enabling them to feed on tougher algae, including encrusting calcareous forms. In turn, they are preyed on by crabs, gulls and fish.
Chitons are only active at high tide, and return to their original position when the tide recedes, possibly guided by a mucous secretion deposited on the outgoing trail. Their pace is slow – look closely and you'll just about discern movement as they gently glide along the rocks.
So, next time you make it down to the seashore, take a moment to turn over a stone or peer among the anemones and fronds of brightly coloured seaweed, and see if you can spot these ancient, fascinating denizens of the rockpool.
Chiton facts
Chitons possess a heart, an open blood system, a pair of kidneys and a simple nervous system.
Chitons have no eyes in their head, but they can ‘see’ through their shells using minute sensory organs called aesthetes, not found in any other group of animals.
The sexes are usually separate and gametes are released into the sea.
The dictionary definition of a ‘chiton’ is a long woollen tunic worn in ancient Greece (from the Greek chiton), or any primitive marine mollusc of the genus Chiton that has an overall flattened body with a shell of overlapping plates.
Main image: An antique engraving illustration of chitons © Getty Images