Category Archives: Molluscs

For the love of sea slugs…

I love sea slugs a bit more than is probably usual. My other half even made sure I have the t-shirt, which I wear with pride in the Cornish rock pools despite the odd looks it gets me.

Trend setting in my waterlogged wellies and 'I love sea slugs' t-shirt.
Trend setting in my waterlogged wellies and ‘I love sea slugs’ t-shirt. Hannafore beach, Looe.

If you don’t already have your own t-shirt, it might be that you haven’t yet met these amazing little creatures. Unlike land slugs, sea slugs come in a mind-boggling variety of colours and shapes and have cool super-powers.

So, this week I’ve been braving the traditional British summer-holiday weather to find top slugs to convert you to the cause. My lucky t-shirt worked its wonders…

If you follow my blog, you might remember my excitement earlier in the year at finding the rare Calma gobioophaga sea slug, which feeds on the eggs of gobies (fish).

It’s probably fair to say that a woman in an ‘I love sea slugs’ t-shirt has never been so excited as I was when I turned a stone this week in Looe, to find three sea slugs with some clingfish eggs. This was another new species to me – the equally rare Calma glaucoides.

Calma glaucoides and its eggs. See how pretty sea slugs are!
Calma glaucoides and its eggs. See how pretty sea slugs are!

This slug has striking long wavy cerrata (tentacles) down both sides of its back, with blueish glands running through them. The pattern of white circles on its back (part of its reproductive organs) help it to blend in among the white scribble-patterns of its egg strands.

The clingfish eggs on which Calma glaucoides feeds - there weren't many left under this rock.
The clingfish eggs on which Calma glaucoides feeds – there weren’t many left under this rock.
Calma glaucoides sea slugs
Calma glaucoides sea slugs – I have no idea what the collective noun would be.

Most sea slugs are ruthless carnivores, but not the Elysia viridis, which feeds on codium seaweed. For some reason up until now, I’ve tended to find blandly coloured brown specimens which don’t show their magic trick very well.

This week, I’m delighted to bring you an Elysia viridis in its finest regalia of green with vivid blue-green spots.

The photosynthesising sea slug - Elysia viridis, grazing on Codium tomentosum seaweed.
The photosynthesising sea slug – Elysia viridis, grazing on Codium tomentosum seaweed.
Elysia viridis showng the green colours and turquoise spots of the chromatophores it stores
Elysia viridis showng the green colours and turquoise spots of the chromatophores it stores

These colours contain chromatophores from the seaweed that the slug has eaten. In other words, it manages to retain the photosynthesising cells from plants and store them in their bodies where they continue to produce energy for the slug.

I almost popped with excitement when, after finding so many fabulous slugs, yet another one turned up during a rock pool event with Looe Marine Conservation Group. Rummaging on the lower shore for exciting crabs, starfish or squat lobsters to show the kids, I spotted some eggs belonging to a slug, the Sea lemon.

Next to a big clump of Sea lemon eggs (left) is a much smaller spiral of eggs
Next to a big clump of Sea lemon eggs (left) is a much smaller spiral of eggs

This egg spiral, in itself, was fairly commonplace but in its midst and alongside it, I noticed two more tiny spirals of spawn laid by something else that I didn’t recognise. After another minute of staring at the rock I spotted the slug.

A pale-coloured Favorinus branchialis sea slug
A pale-coloured Favorinus branchialis sea slug

This slug, the Favorinus branchialis, has two pretty groups of red-ish cerata along its back and a distinctive bulge in its rhinophores (the tentacles on top of its head). It is variable in colour and it took me another minute to spot the second slug, which was much paler, but with the same body form.

The darker of the two Favorinus branchialis sea slugs, showing the bulge in its rhinophores (the antennae on top of its head)
The darker of the two Favorinus branchialis sea slugs, showing the bulge in its rhinophores (the antennae on top of its head)
Favorinus branchialis swimming upside down because it can
Favorinus branchialis swimming upside down because it can

Cute and pretty though it is, this slug has a rather gruesome habit; it likes feeding on the eggs of other slugs. It was no accident that these slugs had laid their eggs right next to those of the sea lemon.

A slug with some serious weaponry turned up on my next foray into the pools.

Berthella plumula sea slug
Berthella plumula sea slug

The Berthella plumula slug (or Feathered Bertha as I call it), resembles a sherbet lemon, but is far more squidgy. I’d never advise actually squidging one, mostly because it’d be cruel, but also because they can secrete sulphuric acid when attacked.

This sea slug has a feathery gill on its underside - unlike most slugs which have their gills in a tuft on their back or in their cerata.
The Berthella plumula sea slug has a feathery gill on its underside – unlike most slugs which have their gills in a tuft on their back or in their cerata.

Interesting defences are common in sea slugs. Many aeolid sea slugs store the stinging cells from the food they’ve eaten, such as anemones or hydroids. If they’re attacked, the stinging cells fire from the tips of the cerata on their backs into their prey. Sea hares, on the other hand, have a similar defence system to squid and cuttlefish, squirting a cloud of purple ink out their bottoms to ward off predators.

Last week, my lucky t-shirt did me proud, so I’m looking forward to getting it on again to explore the shore on next week’s big spring tides. If you’d like to meet these cool creatures for yourself, there are rock pooling events taking place all round Cornwall through the rest of the summer holidays.

Here's your bonus slug for reading to the end - a Rostanga rubra which eats red sponges and is perfectly camouflaged on them.
Here’s your bonus slug for reading to the end – a Rostanga rubra which eats red sponges and is perfectly camouflaged on them.
A charming view of a Favorinus branchialis's bottom. You're welcome!
A charming view of a Favorinus branchialis’s bottom.
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The One That Got Away… Cuttlefish in a Cornish Rock Pool

If you’ve ever been rockpooling, you’ll know the feeling: you’re in the zone, bottom high, head down, lifting a rock or staring into the water when a movement catches your eye. While you’re registering that it’s some interesting creature you’ve never found before, said creature is darting away under an overhang or boulder never to be seen again.

My camera is full of “things that were there only a millisecond before”.

Not the most accomplished photo of a Greater pipefish as long as my arm!
Not the most accomplished photo of a Greater pipefish as long as my arm!

So, you’ll have to take my word for it that I finally encountered an animal I’ve been longing to find in a pool. After four decades of failure, my big moment came while I was taking some friends rock pooling this week.

At risk of overtopping my wellies, I was wading in the centre of a long pool, staring through a clump of Sargassum weed to the sand beneath.  Some baby dragonet fish were zipping from spot to spot and I, as usual, was failing to take a photo of them.

As I bent in close to tease aside some seaweed, a few small creatures shot out. I only had a second to clock that they seemed to be swimming backwards with jerky movements. It was hard to make them out given their sandy colouring, but in the moment it took me to turn towards them and realise what they were, they were gone.

From their shape they had to be either young common cuttlefish (Sepia officinalis) or, very likely, the little cuttlefish (Sepia atlantica). These amazing animals can adapt their camouflage to match their surroundings or to signal their mood. It’s difficult to believe that such mobile, intelligent creatures are a type of mollusc, making them distant relations of limpets and mussels.

Cuttlefish, like this one in an aquarium, are masters of disguise.
Cuttlefish, like this one in an aquarium, are masters of disguise.

Along with an octopus and a seahorse they’re the thing I’ve always wanted to find (in the case of seahorses, I almost definitely never will).

This photo of a cuttlefish was taken in aquarium
This photo of a cuttlefish was taken in an aquarium

Without photos of the cuttlefish or much likelihood of re-finding them in this pool, my excitement was tinged with disappointment. It was going to sound like a tall tale of “the one that got away”.

The second after the cuttlefish disappeared, my eye was drawn back to where they had been. In the water, tails spreading behind them like minuscule comets, were several black blobs.

During their escape from the giant wellies and the hand parting the seaweed, they had fired off their defensive ink. The way the ink formed little clumps suggested they had deliberately mixed the ink with mucus to make it look like little decoy cuttlefish.

With a yelp of delight, I scooped up some ink in a tub and proudly showed my friends and Junior.

Cuttlefish ink in my tub
Cuttlefish ink in my tub

I’m not at all sure they were as impressed as I was.

But at least there’s a chance you’ll believe me that I really did finally see cuttlefish in a rock pool.  Perhaps next time I’ll capture some photos of an actual cuttlefish.

In the meantime enjoy your summer rockpooling adventures and don’t forget there are loads of holiday events for all the family that would love your support (and some decent weather for a change).

Here's one that didn't get away - a large edible crab which impressed my friends far more than my pot of ink.
Here’s one that didn’t get away – a large edible crab which impressed my friends far more than my pot of ink.
I also thought this Aplidium turbinatum sea squirt was rather lovely - and it doesn't move, which is always a bonus.
I also thought this Aplidium turbinatum sea squirt was rather lovely – and it doesn’t move, which is always a bonus.
This lobed sponge (Oscarella sp.) was a lovely yellow tinged with pink -
This lobed sponge (Oscarella sp.) was a lovely yellow tinged with pink –

A predator among the fish eggs: Calma gobioophaga sea slug

If you read this blog regularly, you’ve probably noticed a pattern: I bimble about the Cornish rock pools looking for an exciting creature, fail completely, then find something unexpected. Well, hopefully you like the format because this week is no exception. I go on a quest to find fish eggs and discover this rare sea slug.

Fish eggs are amazing. If you catch them just as they’re nearing hatching you can see each baby fish staring out, its tail curled tight around its head like a scarf.

So, when Junior announces he wants to go for a big walk, I suggest Port Nadler. This slightly exposed rocky bay is ideal for Cornish clingfish. Their distinctive yellow eggs usually carpet the underside of the rocks and their developing babies are especially beautiful.

Clingfish eggs - with one newly-hatched fish (centre)
Clingfish eggs – with one newly-hatched fish (centre)

Only the tide today isn’t low enough to access the clingfishes’ favourite gully.

I look in the pools and lose count of how many rocks I lift. There don’t seem to be any fish eggs. As the tide drops a little further, I come across some Berthella plumula sea slugs and a sea hare.

A pair of Berthella plumula sea slugs
A pair of Berthella plumula sea slugs

There’s an anemone I don’t recognise. Translucent white all over with a base so wide it looks like a bowl. I later realise it must be the white form of Sagartia elegans (var. nivea).

Sagartia elegans (var nivea) anemone
Sagartia elegans (var. nivea) anemone

Junior finishes his digging in the sand at the top of the beach and wanders over to join me. We lift a rock together and finally here are some eggs. They’re not the yellow clingfish eggs I was looking for, they’re smaller goby eggs, forming black-specked carpet of grey. Under the camera, the specks become a sea of eyes looking up at me.

It takes me a long time to decide that the Calma gobioophaga sea slug (in the background here) is 'a thing'
It takes me a long time to decide that the Calma gobioophaga sea slug (in the background here) is ‘a thing’

I remember rockpool expert David Fenwick, who runs the fabulous Aphotomarine site, telling me a year or two back that there was a species of sea slug that specialises in eating these eggs. I peer into the greyness and see nothing, apart from a thin yellowish patch in the centre which looks like a piece of sponge or sea squirt.

I look some more. The eggs around the edge of the yellow patch look longer than the others.

I stare, stare some more then focus my camera on the patch and do yet more staring. Even then I’m not sure, but it could be…

It’s only when I see a tentacle move that I begin to see the slug properly. It’s over a centimetre long, but most of its body is covered in pointed cerrata the colour and shape of goby eggs, right down to the black dots that ressemble eyes.

Calma gobioophaga on its goby egg prey, its eyes showing through behind its long rhinophores.
Calma gobioophaga on its goby egg prey, its eyes showing through behind its long rhinophores.

This is the weirdly named Calma gobioophaga egg-eating sea slug. It’s the first I’ve seen and only the second record of this species in Cornwall.

The yellowish patch I thought was a sea squirt is the slug’s back. It’s covered in pale circles, which my books tell me afterwards are the mature gonads. Who’d have thought?

The books also tells me that the slug absorbs the fish eggs so well into its gut that it has no need of an anus. That’s right; it doesn’t poo. I’m not sure how that works, but it’s the sort of fact that gets Junior’s attention.

Calma gobioophaga - the cerrata (tentacles) on its back blend perfectly with the goby eggs. Only the pale circles on its back (gonads) stand out.
Calma gobioophaga – the cerrata (tentacles) on its back blend perfectly with the goby eggs. Only the pale circles on its back (gonads) stand out.

It’s not the easiest thing to photograph: a grey blob on a mat of grey eggs on a grey day in silty water. As I start to get my eye in to the outline of the slug, it glides towards me, feeling the eggs with its tentacles and swinging its long rhinophores forwards.

Tucked immediately behind each rhinophore is a distinct black eye, one of the characteristic features of this species.

Calma gobioophaga on goby eggs (probably the eggs of a rock goby) near Looe, Cornwall
Calma gobioophaga on goby eggs (probably the eggs of a rock goby) near Looe, Cornwall

The books suggest this species only eats the eggs of the black goby (Gobius niger), but slugs are not great readers and the other records from Cornwall and Brittany are, like this one, probably on rock goby (Gobius paganellus) eggs. In the Mediterranean this species has also been recorded on giant goby (Gobius cobitis) eggs. There’s another, closely related, species of sea slug, Calma glaucoides, that feeds on a wider range of eggs, including clingfish eggs and has been recorded in Cornwall too. Hopefully I’ll find that one soon!

The slug’s life cycle intigues me. As fish eggs are available for such a short period of the year, I’m not sure what happens to these slugs during the remaining months.

It comes on to rain heavily and as we’re already soaked from exploring the rock pools, we call it a day. I haven’t found a single clingfish egg, but, as is the way with rockpooling, I’ve discovered something even better.

A Shell Collecting Bonanza on Looe Beach

After a week of ear-numbing northerlies, the low January sunshine is at last winning through. Junior sets to work with his bucket and spade, attempting to create a sand fort that can be seen from space while I take a stroll at the water’s edge.

Looe Beach - a herring gull is also checking out the pile of shells at the water's edge
Looe Beach – a herring gull is also checking out the pile of shells at the water’s edge

The stretch of sand that forms Looe beach is ideal for summer holidaymakers to lounge on, but generally offers little to the rockpooler, unlike the surrounding shores. Today is different; probably due to a combination of large tides and strong winds from an unusual direction.

Glistening mounds of shells are heaped the length of the shore, and are being nudged onwards by the incoming tide. They crack under my feet despite my efforts not to trample them. 

Shells on Looe beach
Shells on Looe beach

It’s not unusual to see the odd limpet or a few mussel shells here – the harbour is carpeted with them – but this haul of shells is not just large, it’s more diverse than usual. There’s such a kaleidoscope of blues, whites, oranges and pinks that I have to get in close to focus on individual shells.

Shell colours and patterns - a carpet shell (above) and scallop (below)
Shell colours and patterns – a carpet shell (above) and scallop (below)

Among the shells, emerald-green strips of sea grass glow in the sunlight.

Sea grass in the January sunlight at Looe beach.
Sea grass in the January sunlight at Looe beach.

Many of the shells are fresh, some still alive, while others are worn down to their mother-of-pearl lining. I throw the live ones back into the water although it’s probably too late.

A Grey topshell worn down to the mother-of-pearl layer
A Grey topshell worn down to the mother-of-pearl layer
A sea-worn turban top shell (recognisable by the crinkled, 'jelly-mould' shape to the upper face of the shell.
A sea-worn turban top shell (recognisable by the crinkled, ‘jelly-mould’ shape to the upper face of the shell.

Most of these shells are molluscs, either sea snails (gastropods) or clam shells (bivalaves), but among them lies a remarkably intact sea potato. These fragile urchins come from the echinoderm (‘spiny skin’) family and are related to starfish and sea cucumbers. When alive, sea potatoes are covered in bristly spines and live in muddy-sand burrow. These spines quickly rub off if the animal is washed out of its home. What’s left is this white potato-shaped shell.

Sea potato (urchin) on Looe beach
Sea potato (urchin) on Looe beach

I’m soon absorbed, staring into the mass of shells. There’s nothing particularly rare here, but I never could resist shell collecting.

A tiny cowrie shell - Looe beach.
A tiny cowrie shell – Looe beach.

I’m especially pleased with the cowrie and the Auger shell (easily recognised by its twisting tower shape).

Auger shell (Turritella communis) on Looe beach
Auger shell (Turritella communis) on Looe beach

Before long the tide’s rolling in and Junior wants my help to fortify his sand constructions against the waves. As the sun retreats over western side of the valley, the January chill returns and we walk home in the evening glow. Below the cliffs I can still hear the sound of the waves pushing shells up the beach.

Razor shells burrow in the muddy sand near Looe beach.
Razor shells burrow in the muddy sand near Looe beach.
This thick-lipped dog whelk was still alive so I put it back in the sea for a second chance.
This thick-lipped dog whelk was still alive so I put it back in the sea for a second chance.
Time to go home.... A fishing boat returning to Looe harbour as the sun sets behind West Looe Hill.
Time to go home…. A fishing boat returning to Looe harbour as the sun sets behind West Looe Hill.

 

Home from Home: Quiberon in Brittany

Things have been quiet on this page the last couple of months. Cornish Rock Pools Junior, Other Half and I took an extended holiday to visit the towns and beaches of Brittany. As always our travels had a bit of a marine theme…

Est-ce que c’est un anémone?” the eager child in the dark-rimmed spectacles asks. We explain what a ‘stalked jellyfish’ is to the class of seven-year-olds. “Jellyfish!” they chant.

 

Stalked jellyfish - a Lucernariopsis cruxmelitensis.
Stalked jellyfish – a Lucernariopsis cruxmelitensis.

Between fascinating excursions to the fire station and the sardine factory, we are giving impromptu English lessons to a class of primary school students during our twinning visit to Quiberon in Brittany.

 

We have covered the words goby, crab, jellyfish and shark so far and there’s still a sea of raised hands. The children seem desperate to tell us about their finds around the shores of Quiberon. Continue reading Home from Home: Quiberon in Brittany

Hatchlings in the rock pools at Port Nadler

A sunny bank holiday weekend followed by a sunny half-term week is nothing short of a miracle. That the second weekend also coincided with some big spring tides is more amazing still.

I’ve seen some wonderful photos this week of rockpooling finds all around Cornwall. Some fabulous creatures. And if you haven’t been able to explore the shore yourself, Springwatch tonight (8th June) are going to be showing footage of the remarkable comeback of the Clybanarius ethryropus (nope, still can’t pronounce it) hermit crab, filmed with Cornwall Wildlife Trust at Castle Beach, Falmouth.

The stars of my pretty perfect day of wading through pools in the blazing sunshine at Port Nadler, near Looe, were the baby fish.

There are plenty of young fish around at the moment but the new hatchlings can hard to spot. I took this photo of clingfish eggs to capture the eyes staring out of each eggs and the little spotty tails curled round them.

Clingfish eggs hatching in a Cornish rock pool.
Clingfish eggs hatching in a Cornish rock pool.

It was only when I uploaded photo to my laptop that I realised I’d managed to capture my first hatchling (in the centre of the picture). I can’t get enough of those golden eyes.

A recently hatched Cornish clingfish among its egg-bound siblings
A recently hatched Cornish clingfish among its egg-bound siblings

Fish often stick around to guard their eggs and sure enough there was a proud parent next to this rock.

An adult Cornish clingfish showing the typical beaky nose, antenna by the eyes and blue patches on the head.
An adult Cornish clingfish showing the typical beaky nose, antenna by the eyes and blue patches on the head.

I was up to my waist between rocks leading to the open sea when I saw this pale creature, about 4cm long, wriggling amongst the darker kelp. From its elongated, looping form I expected a worm.

A recently-hatched Greater pipefish baby.
A recently-hatched Greater pipefish baby.

On closer inspection the large eyes and fins were clear. This is the first time I’ve ever seen a baby pipefish.

A baby Greater pipefish with yolk sac still attached. The large eyes and long snout are reminiscent of its cousins, the seahorses.
A baby Greater pipefish with yolk sac still attached. The large eyes and long snout are reminiscent of its cousins, the seahorses.

Judging by the yolk sac still attached to its belly, this little fish hatched very recently. I saw several more in the water, their curling movements reminding me of their cousins the seahorses. I wondered if the dad was close by – like seahorses, the male pipefish looks after the gestating eggs in his pouch until they hatch – but he’d be too well camouflaged to spot in this seaweed.

 The rocks were crawling with crabs and the pools were busy with the fry of larger fish that use these sheltered waters as nurseries. My camera battery was low, but this Limacia clavigera sea slug was worth draining my battery for.

A Limacia clavigera sea slug on the move.
A Limacia clavigera sea slug on the move.

 The water was so warm after a week of sun that I put on my snorkel for the first time this year and enjoyed a leisurely float across the bay, watching wrasse skirting the rocks and snakelocks anemones waving in the current. 

If this weather carries on, I can see myself returning to Port Nadler regularly this summer to watch the baby fish growing up.

Cornish Rock Pools junior drying off in the sunshine at Port Nadler, near Looe.
Cornish Rock Pools junior drying off in the sunshine at Port Nadler, near Looe.

Rockpooling at Hannafore – Video

A variegated scallop opens up showing its multiple eyes then snaps shut. A topknot flatfish skimming along the sand. Just some of the creatures I saw in the rockpools at Hannafore, Looe today on the low spring tide.

I was a too busy taking kids ‘shark hunting’ to take more video today. It was a successful mission; we found more than twenty live egg cases of the Nursehound (Scyliorhinus stellaris) and one live Smallspotted catshark (Scyliorhinus canicula) egg case. There were all sorts of other treasures too.

I’m already looking forward to doing it all again tomorrow.