This week's species is the humble limpet. Actually, limpets are a group, Patellogastropoda, not a species. The most common species in the UK is, surprise surprise, the Common Limpet (Patella vulgata).
All limpets, vulgata or not, share a similar body plan. If you managed to pull a limpet off a rock and looked at its fleshy underside, you would see a oval-shaped mouth and 2 main tentacles called cephalic tentacles, at the base of which are a pair of primitive eyes. Most of its underside consists of its single foot, surrounded by the mantle, a soft outer body wall. Around the edges of the mantle, there is a ring of tiny, feathery tentacles called pallial tentacles.
A limpet's underside
If you are walking along the shoreline, you may notice that some rocks have ring-shaped indentations in them. They are created by limpets, and are known as home-scars. A limpet will make one by rubbing its shell against the rock until its shell can fit snugly into the indentation. Each individual has its own home-scar, and will stay there while the tide is out. By clamping down into the home-scar, they create pockets of sea water inside their shells, allowing their gills to still function.
Common Limpets and some home-scars
When the tide comes in, the limpets leave their home-scars and go foraging for algae. They have a tongue covered in teeth-like serrations, which it uses to scrape the algae from the rock. Each individual has its own grazing territory, and if another limpet enters it, a fight will probably ensue. The limpets will ram their shells together, and attempt to knock the opponent off the rock.
Everywhere a limpet goes, it leaves a slime trail, which it follows back to its home scar as soon as the tide begins to go out. It is thought that the slime also acts as a fertilizer, helping the algae to grow back. This way, the limpet hardly ever runs out of algae in its grazing grounds.
Several species of predatory starfish readily attack limpets, but these intertidal molluscs are more vicious than you might think. The smaller limpets will simply hunker down onto the rock, but the larger ones fight back. They will wait until the starfish has the tip of one of its arms under the limpet's shell, then it'll slam the shell down. This creates painful, deep cuts and sometimes even severs the tip of the limb. After several slams, the starfish usually leaves the limpet in peace.
I'm still researching the life cycle. There seems to be various interesting things about it, including a gender change. However, the information is a bit sketchy, and several texts contradict each other. When I've got more information, I'll update this post.
It's plain to see that the humble limpet, mundane and boring at first glance, is in fact a fascinating creature.
Until next time, keep on the wild side!