After many days of getting drenched every time we step outside, Junior and I decide to make the most of the warmer weather and have a lazy day pootling about our local area. If everyone else is taking a holiday in Cornwall, so can we! The rocks between Plaidy and Millendreath are perfect for clambering and exploring, and I promise Junior a spot of wave jumping when we reach the sand beyond.

“I’ve found a blob,” Junior calls over to me.

I am kneeling among some seaweed at the top of a deep rocky gully. My head is almost pressed against the minute Dynamene pumila hydroids that grow on this seaweed, looking at what I’m sure is Doto sea slug spawn. “What kind of blob?” I ask.

“I think it’s a slug,” he says, and I’m up and at his side in a second.

The blob is bigger than I expect, almost like a small anemone on the rock. We stare at it closely, our heads touching. It looks as though it is tipped with blue.

“Oh my word,” I say. “I think you’ve done it.”

We hug and cheer and do a little slug dance, because every slug deserves a dance and this one is especially special. For weeks now, we have been looking for Antiopella cristata, a slug which ought to be found here but which I have never seen.

Taking great care not to harm the slug, we transfer it to a pot of seawater and watch it floof up.

The slug’s body is yellowish, but its back is covered in large waving cerata, each tipped in pale, frosted blue. The effect is like opening a geode to find tall, pointed blue crystals inside.

We call the slug ‘Aunty Crystal’ to help remember its scientific name.

We have named this gully ‘slug alley’ for a reason and plenty more creatures, slugs and others, are hiding on the tall, shady rock face. I find several bright red Rostanga rubra slugs munching on the red sponges.

A tiny ghost-white slug has been laying its eggs nearby. In the water it takes on a frilly appearance, making it look ever more spectral.

Sea cucumbers adore this area and are to be found everywhere, with their bodies hidden in holes in the rock and just their black and yellow mouths protruding. The two main species I see are Pawsonia saxicola and Aslia lefevrei.

When submerged, they will open a wide fuzz of frilly tentacles to feed.

We clamber over the rocks onto the sand, helping a stranded rockling back into a pool on the way, and splash in the waves for a while.

A couple of shells roll past my feet, tumbled by the waves over the silty sand. I make a quick grab for them and, sure enough, they both contain hermit crabs. At low tide, I occasionally find this species here, easily recognised by its enormously long left claw. These crabs are both south-clawed hermit crabs, also known by their gladiatorial sounding scientific name, Diogenes pugilator.

They are ready for battle, almost falling out their shells in their attempts to dislodge my grip, unaware that I am saving them from the herring gulls that are lurking at the water’s edge.

Junior and I kneel at the edge of a sandy pool and pop the hermit crabs in. We watch one emerge without hesitation. The tips of its claws come first, then the stalked eyes and finally its long hairy antennae. The hermit crab hoists its shell up and runs a few paces.

With a furtive glance about it, the crab swings its vast left claw inwards, shoveling sand into a pile while simultaneously flicking the sand over its back with its little right claw. Grains of sand are flung up through the water and by the time they have settled, only the back of the shell and the tops of the hermit crab’s eyes are visible. It is buried out of sight.

We take the hermit crabs back to the sea, leave them as far out as possible – safe from predators – and carry on wave hopping until the tide turns, when we too must head for home.

Here’s a little video of this week’s highlights from the Cornish rock pools. Sit back and enjoy!

If you would like to find out more about rock pool wildlife or go on your own rock pooling adventures, be sure to pick up my books Rock Pool and Beach Explorer. Out now with September Publishing and available from all book shops and online.