Hairy Knees

Whilst at the beach yesterday, I spotted a newly washed up log. Clearly this particular log has led a pelagic existence of late, totally decorticated and covered in marine alga on the underside. I spun it over to reveal the submerged side and noticed several small (2-3mm long) isopods huddled together. Through the handlens I could see that they appeared to be Jaera and their very small size suggested that they were either immature or males. I hoped they were males, as that would allow me to key them through to species. I popped four into a pot and hoped for the best.

Back indoors I discovered that one had promptly died in the tube. Whacking it under the microscope allowed me to confirm that it was indeed male and hence keyable to species - good stuff! 

By using the FSC's Intertidal Marine Isopods and with further reference to The Handbook of the Marine Fauna of North-West Europe I quickly confirmed that it was in the genus Jaera, then had to check the shape of the preoperculum. The preoperculum is a plate found on the underside of the male's body, it lies just beyond the centre of the last abdominal segments, in effect the underside of the 'tail segment'. It can either be narrow and pointed or wide and T-shaped. Mine was the latter. Here's the pic from the book

And here's an image of the dead specimen as seen down the barrel of my microscope

What a beautiful match

This takes us away from Jaera nordmanni with its pointed preoperculum and points us towards the Jaera "albifrons" group, comprising several very similar species. 

Rubbishy pic showing the "sparse fringe of spines" on the abdominal plates

Next I had to take a very close look at the rearmost two pairs of legs and examine them for bulges and tufts of setae, or lack of. In the end I had to kinda dismantle the legs, it was just too difficult to see what was happening in amongst the tangle! 

No bulging lobe on the carpus, which was good news because that ruled out Jaera albifrons - the only species of Jaera I've previously recorded. Next up, I had to examine the upper part of the leg for a cluster of curved setae (setae are strong, bristly things that look a lot like hairs). Here's the pic from the book, very helpfully arrowed

Patch of "knee hairs" on the outer face with three diverging, curved hairs on the inner face

And here's what the rear leg of my beast looks like

That looks about right to me!

Happily, there's only one species in British waters that exhibits a "cluster of curved setae on the distal portion of the ischium" and that is Jaera ischiosetosa, a lifer for me and also (obviously...) "new" to Skye! 

There's a great photo gallery of the species on Dave Fenwick's Aphotomarine page which shows a lot more detail than my images do. 

Whilst manhandling 2mm isopods from the log into a pot, I noticed what looked to be a tiny leech crawling across the wet log. I popped it into the pot, just in case I could do anything with it. Well guess what, it wasn't a leech at all!

This 4mm cutie is an immature Limapontia depressa, a small sea slug that browses Vaucheria alga (a green seaweed) in saltmarshes. Technically I was slightly below the saltmarsh, but it's a dirt common species and supposedly abundant. Immatures can be found crawling across the surface of mud, clearly I need to spend more time with my knees wet and nose pushed down into the gloop!  I've never seen Limapontia depressa before, so deciding to have a quick look at that washed up log turned out to be a good move. 

Anyway, I have a day off work today and it seems that (miracle of miracles) the rain has pushed through and the afternoon could be mostly dry. Ish. Time to go find me some more goodies!