Tag Archives: nudibranch

The Legendary Slug Formerly Known as Discodoris

The tide has turned and I am reluctantly preparing to leave one of best rock pooling beaches in Cornwall after a fabulous few hours in perfect conditions in the company of great friends. As you’d expect, the day has been full of interesting finds, from sponge-covered spider crabs to golden clutches of clingfish eggs. My camera batteries are running low and my hair is dripping with seawater from all the time I’ve spent poking my head under seaweed-festooned overhangs. The kids migrated up the beach a while back to investigate the picnic bag but us adults can’t bear to leave the pools. As the water creeps up my wellies, I gently turn one last rock, and then another for luck.

This small species of spider crab (Inachus sp.) was so completely covered in sponges that I couldn't see her shell at all.
This small species of spider crab (Inachus sp.) was so completely covered in sponges that I couldn’t see her shell at all.

I let out gasp so loud that it would make most people think I’d just broken a bone, but my friend knows better. She moves closer to ask what I’ve discovered, but I’m so overwhelmed with excitement that I can only babble about having, “finally found one”.

I point a trembling finger at the rock. “It’s a Disco…a Discodoris planata,” I stutter, before launching into a garbled explanation of how it used to be a Discodoris has been renamed Geitodoris, but I use Discodoris because I love that name and…

I take a few photos of the cause of my breathless wonder, straighten up and fling my arms over my head and shout at the top of my lungs to attract the children’s attention. It takes me a minute to realise that the distant child I have in my sights is not mine, but  Junior has noticed my flailing and comes scrambling across the rocks with his friends.

We crowd in the fast-filling pool and peer down at my rock. Even Junior is a bit confused by my excitement over the small, brown lump I’m indicating.

Not just a brown lump... Geitodoris planata (the slug formerly known as Discodoris planata)
Not just a brown lump… Geitodoris planata (the slug formerly known as Discodoris planata)

“It’s Discodoris,” I explain, breathlessly. Instantly, he joins my paroxysms of delight, shrieking out the great news to his friends and going through the same Geitodoris speech as me, for this unassuming slug has become something of a legend in our household.

This isn’t the first time I’ve ever seen one, but it’s the first time I’ve had a working camera with me and it’s the first “Discodoris” that Junior has seen. He is especially impressed with the white star patches on the slug’s back. These are glands which secrete a powerful acid, ideal for seeing off predators.

The white patches are powerful acid glands.
The white patches are powerful acid glands.

On close inspection, there’s a pale-yellow blob alongside our “Discodoris” (Geitodoris planata): another slug. At first, I assume from its colour that it must be a Jorunna tomentosa, a slug I often see on this shore. Indeed, there is another Jorunna tomentosa on the same rock. However, this one seems to be getting very cosy with Discodoris. In fact, it looks to me as though they are mating. The yellow slug also has a far flatter profile than any Jorunna tomentosa I’ve seen before.

Our brown Geitodoris planata and its much paler yellow mate getting friendly in the Cornish rock pools!
Our brown Geitodoris planata and its much paler yellow mate getting friendly in the Cornish rock pools!

If the tide wasn’t coming in, and if I wasn’t called away by someone further up the beach finding a giant goby, I might have been able to check the slug’s underside. If I’d done that I could have seen without doubt that this was a second “Discodoris”, a two-for-one package. The underside of Geitodoris planata is fringed in brown spots, unlike the very similar sea lemon, which is all one colour.

The fish found by some holidaymakers was indeed a giant goby. These fish are a protected species so must not be caught or disturbed without a licence. We left it hiding in its surprisingly small pool.
The fish found by some holidaymakers was indeed a giant goby. These fish are a protected species so must not be caught or disturbed without a licence. We left it hiding in its surprisingly small pool.

Fortunately, social media now enables geeks like me to swap photos with other slug-loving types and sure enough, Geitodoris planata, though usually brown with distinct white acid glands, can sometimes be pale.

Although I will record the slug as Geitodoris planata and there are important scientific reasons for the name change, this little animal will always conjure up glitter balls and platform shoes in my mind. To take photos of the fabled Discodoris, and a mating pair at that, has to be the perfect end to a perfect day.

Geitodoris planata pair
Geitodoris planata pair
Shining like pure gold - the eggs of the Cornish clingfish (Lepadogaster purpurea).
Shining like pure gold – the eggs of the Cornish clingfish (Lepadogaster purpurea).
Jorunna tomentosa slug
Jorunna tomentosa slug
One pool on the mid-shore was home to scores of colourful St Piran's hermit crabs.
One pool on the mid-shore was home to scores of colourful St Piran’s hermit crabs.
Another species of hermit crab - the tiny Anapagurus hyndmanni
Another species of hermit crab – the tiny Anapagurus hyndmanni
Sarah's common eel - our last find of the day before my wellies overtopped!
Sarah’s common eel – our last find of the day before my wellies overtopped!

“The slug formerly known as Discodoris” and a host of other rock pool creatures feature in my book Rock Pool: Extraordinary Encounters Between the Tides. Out now online and in book shops nationwide from September Publishing. If only I’d found one in time to include a photo in the book…

Warming up for the Weekend

Spring tides and slightly more spring-like weather might finally coincide this weekend, so I’m preparing for a big weekend of rock pooling. If all goes to plan, I’ll be reporting back next week. In the meantime, I’m readying my waterproofs, planning which beach I’ll go to according to the wind direction and sorting out my photos from the last month. And of course, I’ll be at the Looe Marine Conservation Group Rock Pool Ramble on Monday at Hannafore beach, so maybe I’ll see you there?

One beach I’m hoping to visit on Saturday is Millendreath. This sheltered south coast beach has an interesting geological history. Somewhere under the sand is a submerged ancient forest. Whether the nutrients come from there, drift along from the Looe river, or both, this beach has a unique fauna and is always full of surprises.

Pheasant shell at Millendreath
Pheasant shell at Millendreath

In the past I’ve found masked crabs, weever fish and unusual swimming crabs here. On my visit last week, it was all about the sea slugs and cucumbers.

In the chilly breeze it felt less than spring-like, but these things seem not to bother the rock pool creatures. Sea lemons, a type of sea slug with a big circle of feathery gills on their back and pocked citrus-like skin, were everywhere.

Sea lemons - a type of sea slug - enjoying each other's company.
Sea lemons – a type of sea slug – enjoying each other’s company.

And so was their spawn.

A spiral of sea lemon spawn at Millendreath
A spiral of sea lemon spawn at Millendreath

A species that seems to love the conditions here is the brown sea cucumber, Aslia lefevrei, which likes to hide away in holes in the rock with just its retracted tentacles sticking out. When these are fully extended they have a frilly, carrot-top appearance, but at low tide all we see is a yellow and brown blob.

Brown sea cucumber, Aslia lefevrei, at Millendreath
Brown sea cucumber, Aslia lefevrei, at Millendreath
The tip of a brown sea cucumber, Aslia lefevrei
The tip of a brown sea cucumber, Aslia lefevrei

Among the seaweed at the edge of the shore, I spotted a fleck of orange. Old seaweeds often turn bright colours as they die back, but this fleck wasn’t attached to anything. After fumbling about in the cold water for as long as I could bear, I managed to scoop the fleck up and tip it into a petri dish.

Much of my time on the shore is spent staring at things, wondering if they’re animals or just tricks of the imagination. Often they’re nothing, but this one was definitely a something.

My blob - a Eubranchus farrani sea slug with 20p for scale
My blob – a Eubranchus farrani sea slug with 20p for scale

As it settled in the water, the blob began to unfurl and then to secure itself to the dish. It was definitely a sea slug, although still quite hard to see as you can tell from its size compared to the 20p piece.

Eubranchus farrani sea slug - close-up
Eubranchus farrani sea slug – close-up

The chunky cerrata on its back and the orange on its body were typical of the species, a Eubranchus farrani. By far the smallest one I’ve ever seen.

Conditions were too cold to spend any longer with my hands in the water, so I retreated to the upper shore to look for anemones with Junior and to let him dig around the stream. Perhaps one day he’ll dig down to the submerged forest?

Beadlet anemone in a pool near the top of the shore, Millendreath
Beadlet anemone in a pool near the top of the shore, Millendreath

Even on uninviting, cold days, there are always things to find. Millendreath never fails to surprise me. Who knows what will turn up this weekend? Conditions should be easier, but I’m taking no chances. Other half got a big thermos flask for his birthday and I’ll be filling it with hot chocolate before we go out!

Xantho hydrophilus crab
Xantho hydrophilus crab