Fairer conditions set in for the second day of rockpooling with the fabulous David Fenwick and the Coastwise North Devon team. Without the challenges of wind-blown pools and rain-spattered lenses to contend with, the day promises to be even more inspiring.

I’ve managed to replace Cornish Rock Pools Junior’s leaky wellies so he joins us to track down amazing creatures. Today we will focus on the lagoon and seagrass beds at Hannafore and I have no doubt I’ll be seeing something new.

Junior gets stuck into the task at hand; head down, bottom up, staring into the glassy water. He shrieks and comes wading over to me, taking care not to spill water from his precious tub. In it he has a plump sea slug, a ‘Great grey’ Aeolidia papillosa – or sheep slug as we call them.

It’s a rusty colour from eating anemones and I’m allowed to stroke it. “It feels barely there, like air,” Junior explains. He looks after it for some while before returning it to the exact spot he found it.

I sight a little yellow blob and pop it in a plastic tube, expecting it to be a Lamellaria mollusc. A few minutes later it’s sprouted rhinophores on its head and is circling the tube like a hamster in a wheel. It’s a Jorunna tomentosa sea slug.

Meanwhile, David Fenwick is making amazing finds. He’s especially interested in the small spider crabs today and is keen to identify some more species. It pays off – by examining one under a microscope before returning it to the shore he discovers an Achaeus cranchii, last recorded in 1909. David has posted his fantastic photos on his site Aphotomarine here: http://www.aphotomarine.com/crab_achaeus_cranchii.html

Someone points out these stunning Eubranchus faranni sea slugs to me. They’re some of the most spectacular little nudibranchs I’ve ever seen. Although their body shape is the same, the two slugs are entirely different colours: one orange, one black. Both are feeding on hydroids (the tiny fern-shaped animals that you can see on the seaweed).

We all keep an eye out for baby cat sharks as this area is a nursery for their egg cases and we often see hatchlings this time of year. Rob spots one, a recently hatched greater spotted catshark (Scyliorhinus stellaris) and we all gather to look at it. Junior touches its rough back and watches it swim a short distance.

When the tide turns we start to make our way back to shore; the water floods in quickly across these shallow lagoons and can easily catch you out. As usual, this is the moment when I make my best find. I’ve just said to Jan from Coastwise how nice it is not to look at stalked jellyfish, which, pretty as they are, are frankly becoming a bit tedious after a whole winter of dedicated surveys to record them. Then something catches my eye.

Yes, it’s a stalked jellyfish, but this one is different. It’s a Calvadosia cruxmelitensis, always a pretty species, only it appears to have a reflection behind it, an exact mirror image. Closer inspection confirms that this is a double-headed stalked jellyfish, the first I’ve ever seen. Jan and I take photos as the tide creeps up our boots.

After hours wading through the water, bending down, climbing over rocks and lifting stones, we’re all slump down, exhausted onto the pipeway to munch a late picnic lunch and swap notes while the tide pushes in around our feet.

By sharing our finds and knowledge we’ve all seen new things and I’ve learned a huge amount about this familiar shore.