Diptera.info

Posted by atylotus on 07-01-2012 10:02

You already guessed that it was a Cladoceran for it has a single median dorsal eye, two "valves" on either side of the body and two "legs" which are in fact the antenna. All crustaceans, inclucing Cladocerans, have 2 pairs of antenne. There is also a single true leg, but this is placed at the ventral side of the body, moving between the valves.
However, I think I see a large ventral spine (a pointed extension of these valves), so the genus Daphnia seems the most likely candidate. And 2 mm is quit large for a Cladoceran, and to my knowlegde Daphnia reaches this length.

Posted by blowave on 08-01-2012 16:10

You could be right about the dorsal view Moo, but I wasn't sure as the big antenna at the top didn't seem to correspond with one on the opposite side in the first photo. All those in the photo with the Chaobrus larva looked to be swimming with a big antenna at the top, apparently lacking one at the bottom but having some sort of a leg at the bottom or ventral side. The last photo shows two antennae, equally on either side.

atylotus, I had a lot of what looked like Daphnia within a very short time of building and filling the pond in 2009, since then I have had ducks which visit from late February for a few months then they disappear but they must feed on these. There's also a lot more foliage cover so I can't see as much as I did in the first few months!

The Daphnia I have seen all look to have an eye and antennae near the 'head' end, this has both further back much more like a Cyclops but it doesn't seem to fit any of thos I can find either. I have found several keys but can't fit this anywhere. There is a picture based key albeit in the USA but Ihaven't found anything close there either..

http://cfb.unh.ed...index.html

There might be something in this pdf but I haven't been able to pick anything out, there's 75 Cladocera of which 73 are present in the UK.

http://www.boxval...osters.pdf

The pdf is from Norway, I couldn't get the site link last night but it's now coming up..

http://www.nina.n...ceans.aspx

Links from the Cladocera Interest Group UK, I may be able to find more out there but thought someone here might recognise it.

http://www.boxval...ads.asp#SP

I have photos from September 2009 of a few different Cladocera, there was a lot of very small ones similar to this, the one with the egg shell nearby gives an idea of the size. The egg case was ~1mm or very slightly more in length.

Posted by Tony Irwin on 09-01-2012 19:52

I contacted Adrian Chalkey about this. Adrian runs the Cladocera Interest Group ( http://www.boxval...cindex.asp ). He only looked at photo 3 which I sent to him while the site was down. He said "I've been looking at the photo - or squinting at it I should say, rather blurred so it helps a bit. The swimming antennae seem to have two similar length, long branches - and though you cant clearly see how many segments they have it just seems to me to have the jizz of Daphniidae.
That said the head looks small compared to the body shells. What threw me at first was the long oval shape of the body, then I realised the photo is taken, not from side on, but mostly from above and only slightly from one side, you can just see the two halves of the shell separating below the head. So the angle of the photo distorts the height of the waterflea, compressing it, though the width is correct. Allowing for that, with the small head and relatively large radius of the shell below the head I'd say it is probably a Simocephalus species. Obviously I can't say if it is S. vetulus, S. exspinosus or S. serrulatus, the three species we have in Britain.
Interesting photo, I'm far too used to seeing Cladocera under a microscope at 90 degrees or whilst alive and moving so it's good to try to work out a still image taken whilst swimming. I don't get sent many casual snaps of waterfleas!"