Category Archives: Molluscs

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.

 

Worms, slugs and jelly

As anyone who spends time around children knows, they generally delight in things that adults find yucky. So, what better for a day out with Cornish Rock Pools Junior than a visit to a sheltered, silty shore? It’s the perfect environment for all things slimy.

It didn’t take us long to find one of the strangest – and stinkiest – animals on the shore, the bootlace worm. We turned a stone and on one side was the head and part of the tangled body of the brown worm. The rest of the body spanned across to the next boulder like a rope bridge.

The thin, long body of a bootlace worm stretched between two rocks.
The long, thin body of a bootlace worm stretched between two rocks.

The bootlace worm is massively long – the longest recorded apparently came in at 55 metres, making it the longest animal in the Guinness Book of Records. This one would probably have spanned at least 7 metres. Given the difficulties of unravelling the tangled body without breaking it coupled with the fact it exudes acrid-smelling, toxic mucus, we decided against measuring it.

On another rock we found a prettier creature, the candy-stripe flat worm. This one had moulded its paper-thin body to the contours of the rock. When they’re not oozing along like this, they’re reasonable swimmers, albeit with a technique that resembles a tissue blowing along the pavement.

A small candy stripe flatworm oozing along its way.
A small candy stripe flatworm oozing along its way.

We started the search for jellies. The sheltered clumps of seaweed seemed a likely spot for stalked jellies, although Junior’s fascination with kicking up ‘pyroclastic flows’ of silt did hamper visibility a little. For a while we found nothing but ‘snotworm’ eggs, the green eggclumps of the green leaf worm.

When we did find our first jelly blob, it turned out to be another kiddy favourite, a slug. Out of the water, it was a shapeless splodge of yellow. In the water, it stretched out its white body to display yellow stripes and various yellow appendages and antennae.

Sea slug - Polycera quadrilineata
Sea slug – Polycera quadrilineata

As we watched the Polycera quadrilineata slug’s slow progress along the seaweed, we noticed another, more flowery jelly-blob behind it. This was the first of several Lucernariopsis cruxmelitensis stalked jellyfish we found.

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

The incoming current was throwing up a cloud of silt, but we managed to find eight stalked jellies among this small area of the shore. Not a bad haul of squidgy, slimy, child-pleasing creatures.

Stalked jellies have stinging tentacles like their cousins, the jellyfish, but live attached to seaweed rather than floating in the ocean.
Stalked jellies have stinging tentacles like their cousins, the jellyfish, but live attached to seaweed rather than floating in the ocean.

 Here are some of our other favourites from this expedition:

A sea spider. These delicate little creatures are perfectly camouflaged among the seaweed.
A sea spider. These delicate little creatures are perfectly camouflaged among the seaweed.
Tubulanus annulatus. This strikingly coloured worm was a first for me and is more commonly seen offshore.
Tubulanus annulatus. This strikingly coloured worm was a first for me and is more commonly seen offshore.
I was right at the depth-limit for my wellies when I found this topknot flat fish scooting along the bottom of a pool. Junior loves their asymmetrical faces.
I was right at the depth-limit for my wellies when I found this topknot flat fish scooting along the bottom of a pool. Junior loves their asymmetrical faces.
More slime! Cowries are able to dangle from the rocks using their strong mucus trails.
More slime! Cowries are able to dangle from the rocks using their strong mucus trails. This one’s in typical abseiling position.

Rockpooling Heaven (And a downpour)

The sun is shining and, for the first time in months, I can feel the warmth on my face. With calm seas, the tide has run out even further than I hoped, rockpooling conditions here in Looe are near-perfect. There are ominous clouds looming over the hills behind me, but I choose not to look at them.

Perfect - this sheltered gully has weathered the storms.
Perfect – this sheltered gully has weathered the storms.

After the fierce storms, I half expect to find the rockpools empty, scoured of life, but I couldn’t be more wrong. I explore an area of my local shore in Looe that I don’t often visit and within minutes I have found my new favourite rockpooling spot, a gully that’s visibly wriggling with life. Continue reading Rockpooling Heaven (And a downpour)