Summer Rock Pooling At Millendreath

Irys and her mum are hoping to see a sea slug. As regular readers of this blog will know, I am more than a little slug obsessed, so we quickly hatch a plan to visit “Slug Alley”.

The day is grey and mizzly, as is typical in Cornwall any time of year. These damp conditions are ideal for sea creatures that would hide away on sunnier days to avoid drying out. The tide is nothing special, but there is still a fair chance of finding slugs if it drops enough to allow us to access the deep rocky overhang.

This flat periwinkle is happily searching for seaweeds among the damp sponges and sea squirts.

Tiny blobs of jelly aren’t easy to see, especially when the whole of the rock is coated in an assortment of blobs already. As well as some blobby seaweed, there is a rich turf of sponges, sea squirts and bryozoans, all competing for space in this damp, shaded area.

Star ascidian colonial sea squirts at Millendreath, Cornwall.

Among the hydroids I find a few super-small blobs that might be Doto sea slugs, but out of the water it is impossible to tell. Junior finds a “huge” stalked jellyfish a few centimetres long, which can only be a Calvadosia campanulata.

Calvadosia capanulata stalked jellyfish.

This jelly is common in the summer and can be a few centimetres long. The tiny turquoise spots on the outside of the bell are unique to this species.

Less obvious, but more numerous Haliclystus octoradiatus stalked jellies are everywhere at the moment.

Haliclystus octoradiatus stalked jellyfish.

I even find one under a stone. These stalked jellyfish normally only live on seaweed, so this one has probably been dislodged by something and will try to loop its way back to the seaweed when the tide comes in.

Stalked jellyfish under a stone looking rather sorry for itself!

Irys finds a blob and shows me. It is small, brown and jelly-like and I am pretty sure it is a slug. I try not to get excited until we are sure. Carefully, we remove it from the sponge and pop it in a pot of seawater. In true magic slug style, the little creature sticks itself to the bottom of the tub and begins to open up and move. This is not either of the species I first thought it might be.

Irys’s fabulous find – Aegires punctilucens, a nudibranch sea slug.

We transfer the slug to a shallow petri dish to get a better look. As soon as it is under the camera, it is obvious that this slug is indeed something different. It’s a species I have only seen before in my (many) books and it’s an absolute gem. It even looks like it is hewn out of rock with its bumpy, knobbly back, but between the bumps, the body is smooth, dark brown and decorated with spots of iridescent blue.

Aegires punctilucens sea slug at Millendreath

This is a fabulous find and I am in awe that Irys spotted it having never seen a sea slug before. I have to check the name in a book when we get home – Aegires punctilucens. Punctilucens means points of light shining through or dawning… a perfect description.

Aegires punctilucens sea slug exploring the pool at Millendreath.

We take a lot of photos  of the slug in a petri dish and in a shallow pool before returning it to the rock where we found it, where it will feed on the sponges. Ideally we would take photos of it in situ, but out of the water it really is featureless brown goo!

The tide has dropped a little more, so we explore the pools further down the beach while we can.

Among a forest (or salad garden?) of sea lettuce, I spot this beautiful Polycera sp. slug. It is fairly large for this species and has striking yellow lines.

Polycera sp. nudibranch sea slug.

It is likely Polycera quadralineata, the four-lined sea slug, but it can be difficult to distinguish from Polycera norvegica. This lovely slug likes to eat bryozoans – colonial animals that form mossy sheets on the seaweed and rock – so it can become quite numerous this time of year.

Polycera sp. sea slug at Millendreath

I hadn’t been sure of finding much today on such a small tide, but slug alley has done us proud. We are all delighted with our finds and we are already planning another expedition together next time Irys and her mum visit.

Another creature in an unusual place – Aplidium turbinatum sea squirt on sea lettuce.

If you are visiting the beach this summer, be sure to rock pool responsibly and safely. Check the tides and leave everything as you found it. Read my top tips for successful rock pooling.

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