This guy was just a wee red blob, but I knew it was something interesting from previous observations from up north :-)
The last image has a scale (mm and 1/2 mm divisions), the bell is about 4mm high.
It can curl up its tentacles so they are just little knobs, which it does when swimming. It can then unfurl those tentacles and drift with them extended.
The very same fern as https://www.inaturalist.org/observations/179649516
Certainly one of the most vigorous and best shaped Hard Shield Fern i do know in my home region.
The large fronds are clearly bipinnate, largest forwards directed pinnulae beside leaf midrib are partially pinnate, so this fern's leaves are the same dissected as with large Polystichum setiferum, it's ancestor.
Still the fronds are leathery stiff, with glossy upper side, more bright to slightly yellowish green. Leaf stipe shorter than with P. setiferum, lowest pinnae relatively long, but clearly shorter than longest ones. It's rather bright to yellowish green upper surface is uncommon with P. aculeatum, might be due to growth condition, sunny from east side.
See as well at flickr album Polystichum aculeatum "forma parangulare".
on Fraxinus excelsior
on vertical limestone walls, in the shade
The same as here
https://www.inaturalist.org/observations/178156112