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Slugs, snails and sunshine on my mollusc recording course

You never know what you’ll find on a beach and it’s rarely what you’re looking for. It felt like something of a fluke when an octopus put in an appearance on my mollusc course in Devon last month. I could only hope that some interesting snails and perhaps a slug or two would turn up for this week’s molluscs workshop in Falmouth for the Environmental Records Centre for Cornwall and the Isles of Scilly (ERCCIS).

The sun shone, which is always a good start, and I couldn’t have asked for a more enthusiastic group. After the morning’s presentation and a lot of work on topshell identification, we enjoyed a perfect picnic on Gyllingvase beach, taking care to protect our sandwiches from the herring gulls, before setting out to explore the rocks.

I was showing some of the group the different topshells, winkles and other shells found near the top of the shore, when someone found a coil of eggs under a stone. It was a perfect start – the eggs of a great grey sea slug (Aeolidia filomenae). We looked all around the area and couldn’t see the slug that had laid them, but it was probably still close by.

Great grey sea slug eggs - from another day because I didn't take a photo of ones we saw at Falmouth.
Great grey sea slug eggs – from another day because I didn’t take a photo of ones we saw at Falmouth.

Inspired by our early success, we carried on down the shore and one of the group found some codium seaweed. Remembering that I’d mentioned that the photosynthesising sea slug, Elysia viridis, is often found on this seaweed, she called me over.

The lump on the codium she’d hoped might be a slug was seaweed, but we examined the codium some more and soon found two photosynthesising slugs on it. The shout of, ‘Slug’, went up so that everyone could gather to take a look.

Elysia viridis, the photosynthesising sea slug. This slug retains the chloroplasts from the seaweeds it eats and they carry on producing energy inside its body.
Elysia viridis, the photosynthesising sea slug. This slug retains the chloroplasts from the seaweeds it eats and they carry on producing energy inside its body.

Gyllingvase has all sorts of seaweeds, lots of pools and steep rocky overhangs, which makes it a perfect habitat for snails. We found the egg capsules of the netted dog whelk and the European sting winkle among many other things.

‘Slug!’ The shout went up again, this time for a big brown sea hare (Aplysia punctata) and before long we’d seen several of them. They love the sea lettuce and other seaweeds that are growing rapidly in the pools this time of year. They were congregating all over the beach to lay their pink spaghetti egg strings on the seaweed.

Sea hare, Aplysia punctata
Sea hare, Aplysia punctata

We had another shout, that turned out to be this beautiful candy-striped flatworm. It’s not a mollusc of course, but was still a great find.

Candy-striped flatworm at Gyllingvase, Falmouth
Candy-striped flatworm at Gyllingvase, Falmouth

It was clear there were plenty of creatures to be found and the entire group took the search seriously, crawling on the rocks, staring into pools, lifting seaweed and bringing all sorts of finds to me.

In a kelp-strewn gully at the edge of the sea, we found more snail eggs of various sorts and some live sting winkles. A sea lemon was sheltering in a small hole in the rock, our fourth sea slug species of the day.

The sea lemon, showing its feathery gills (top) and the rhinophores on its head (bottom).
The sea lemon, showing its feathery gills (top) and the rhinophores on its head (bottom).

We put it in a pot of water to watch its rhinophores emerge from its head and its gill feathers unfurl on its back.

By now the tide was starting to turn, so I placed the sea lemon back on its rock and hurried to take a look down another promising gully. There were some anemones about, the favourite food of the great grey sea slug whose eggs we’d seen at the beginning, so I hoped I might find one hanging about there somewhere.

After a few minutes of examining an overhang and taking a look under stones I’d drawn a blank and stopped to take a look at some finds people had brought to me. I was about to haul myself back up the rocks when I spotted a long stone that was half-wedged against the rounded overhang at the back of the pool. It looked like a sluggy sort of stone, one that wouldn’t move easily and might have all sorts of sponges, squirts and other things slugs like to eat growing on or near it.

As soon as I turned the stone, I could see the colourful cerrata of a little slug. It most definitely wasn’t a great grey sea slug with its bright reds and blues. I screamed, ‘Slug!’ loudly enough for most of Falmouth to hear and fumbled with a petri dish, scared I might drop the slug in the water and lose it.

Facelina auriculata sea slug
Facelina auriculata sea slug

The great thing about teaching a workshop is that everyone there is just as excited by marine creatures as me, and this one, a Facelina auriculata, is one of the most beautiful slugs I’ve seen on the shore. It caused a lot of excitement and photo taking.

Facelina auriculata sea slug
Facelina auriculata sea slug

After returning the Facelina auriculata, which we nicknamed ‘the patriotic slug’ due to its red, white and blue colours, I turned my attention to a deep pool to look at some rainbow wrack. Lovely though the turquoise iridescence of rainbow wrack is, it wasn’t the seaweed itself that interested me, but the colony of various hydroids growing on it. These colonial animals are relatives of the jellyfish and anemones and are a favourite food of many sea slugs.

I was hoping to find a Eubranchus farrani, a colourful slug with fat cerrata and orange markings on its body, which loves to eat hydroids. I soon spotted a tiny slug, but it was something different. It was so small I could barely see it, but in the petri dish when it came out fully I could see under my camera’s magnification that it was a Polycera quadrilineata, a pretty white slug with yellow markings and yellow-tipped tentacles.

Polycera quadrilineata sea slug at Gyllingvase, Falmouth
Polycera quadrilineata sea slug at Gyllingvase, Falmouth

It was hard to see much with the naked eye, but we all had hand lenses and cameras to get a close look.

Polycera quadrilineata sea slug, Gyllingvase, Falmouth
Polycera quadrilineata sea slug, Gyllingvase, Falmouth

By this time the tide was rushing in. A last foray along a higher gully produced a cowrie shell and a perfectly orange common starfish, which isn’t a mollusc but made us happy nonetheless.

By the end of the day we’d seen five species of sea slug, the egg spiral of the great grey sea slug and all sorts of snails.  It was the kind of fantastic result that comes from lots of dedicated people searching and a good dose of luck.

I can only hope that my run of workshop luck holds for my jellyfish course later in the year. Who knows what might turn up?

Taking photos of a sea slug at Gyllingvase
Taking photos of a sea slug at Gyllingvase