Rockpooling at Castle Cove, Ventnor, Isle of Wight

I have come to realise, over a lifetime dedicated to identifying wildlife, that I love not being able to identify wildlife.

The intertidal zone is an extremely enjoyable place to visit in this regard. I am unable to identify the vast majority of the organisms that live there.

But on each visit, I familiarise myself again with the few that I can recognise, and chip away at identifying some of the rest. Here are some that I am still chipping away at. If you can tell me what they are, I'd be very grateful. Any pointers, suggestions or ideas gratefully received - please leave a comment.

Sand Smelt Atherina presbyter? 
I'm fairly sure of this, and I've been shown them here before by Theo Vickers. This was one of at least six in clear, shallow water over bare chalk in the lagoon. They were slightly attracted to the torchlight and stayed still for the camera.

Confirmed as Sand Smelt by Seth Gibson.

A mussel. 
Invariably, if I bring back a specimen to examine under the microscope, I discover some interesting bycatch in the tube with it. This tiny (3.3 mm) mussel was bycatch with a sprig of red seaweed. I expect at that size it is a long way from being mature and probably also a long way from being identifiable. But it has an attractively banded shell, and a scatter of perpendicular bristles on both valves which might be ID features. It's the first mussel I've seen at Castle Cove. Bean Mussel Modiolula phaseolina perhaps?

Mystery organism.
Whatever these are, they are fairly common, attached to red seaweeds. A globular ball of sand, firmly cemented to the seaweed, and small - this individual was 4.5 mm on its longest axis. It has two orifices (arrowed), which are just very short, simple tubes that protrude slightly when open, and contract inwards when closed. The coating of sand on its body is very firmly cemented in place and very hard to chip off, but the occupant seems to be just a featureless, colourless blob. I'm now thinking it is most likely a sea-squirt, perhaps a sea grape Molgula, a genus which includes some species that encrust themselves in sand, though they seem also to live partially buried in sand.

I would really like to know what these creatures are, and I'm sure I will find out sooner or later, but I'm also enjoying spending time at the frontiers of my own ignorance!

And without being able to identify everything, sometimes I am forced to simply enjoy observing the diversity of life in the rockpools.

Here's a couple more that I identified, for the first time in my life, after Thursday evening's rock-pooling session:

Pelagella castanea (was Goniodoris castanea) found feeding on some Botryllus schlosseri.

Bycatch: the foraminiferan Elphidium aculeatum (on the basis of a decent match at foraminifera.eu).