Today, I introduce another group of animals which my fellow blogger Argylesock can add to the list of species to race with me when I visit the UK next! By the time I get over there, hopefully we will have a list including some species which move a little faster, otherwise vast quantities of tea will be drunk whilst waiting for the race to finish!
Whilst a range of organisms are called Limpets, these next two posts will focus on one specific group of them, the “true” limpets, Patellogastropoda.
Today’s post is going to be about their shell, morphology (body features) and behaviour. Tomorrow (extra post because I missed Monday) will be about their habitats.
Most people will be familiar with limpets, from the inter-tidal areas on beaches, where they are found on the rocks when the water recedes. This lovely picture is of the one I am most familiar with from my time growing up by the sea, Patella vulgata or the common limpet:
Many limpets have a slightly pointy shell, as you can see in the image above. One of the very cool things about these creatures with shells is, that, unlike us, where you cannot point to a part and say “That is from when they were younger”, with molluscs, they secrete their shell starting from the centre, so the very centre of the shell is from when they first started secreting it.
As with all molluscs, limpets have a radula (the scratchy toothy tongue we covered before), which they use to scrape algae from the surface of rocks.
As anyone who has seen limpets will know, they are usually found sitting on rocks. However, they do leave the rocks to go foraging for extra food between tides, and they follow their mucus trail (like a snail trail) to get back to their comfy spot on the rock. You can see when limpets have been attached to rocks as they often leave a scar there from their shell edges. This indentation from their shell edge means that when they settle down again, the shell digs into the top layer of the rock, which makes them more firmly attached than if the shell was just resting on the surface of the rock.
Although we do not usually see them moving around much, and so may think of them as fairly passive organisms, they are of course, living animals, and so have some defenses against predators (It is not a good evolutionary strategy to sit there and get eaten!). The first video shows one of their defense responses, and illustrates the surprising flexibility of these animals, whilst the second shows feeding behaviour.
So, apart from homing behaviours and acrobatics, what else is cool about these animals? Tomorrow I will cover the coolest thing about these animals (for me, at least), but there is one final thing I want to tell you today.
Patellogastropoda are hermaphrodite, that means they have both male, and female reproductive organs. This is not unusual in invertebrates, or generally within nature, but what is interesting about these is that they are all male to begin with, after the larvae settle onto a rock and they start developing. They mature as males after 9 months or so, and stay male for several years, before the majority of them change to female.
This means that the majority of sperm released is from younger animals, whilst the eggs are released by the older members of the group.