Marine crustacean to identify

[hatless]

I found this very dead thing on a beach in North Wales near fishing boats, so it may have arrived in a lobster pot rather than being washed up.

The two posterior segments have no legs. The next three segments have one pair, and the anterior segment appears to have two pairs of legs, one like those on the other segments, and one pair that is a little stronger - though only a fragment remains. Does this make it a Decapod?

The eight similar legs are quite long, in two sections, and seem to have hairs or bristles on them. They look more useful for swimming than crawling.

[zan]

It looks to me like the exoskeleton of an isopod. Isopods are decapod crustaceans (including ordinary garden slaters) which are mainly aquatic, and are dorsoventrally flattened like your example. The abdominal segments aren't very clear in your photos, but may be fused I suppose. There should be 7 thoracic (anterior) segments and 5 abdominal segments in a standard isopod.

[hatless]

The Googling I've done leads me to believe that isopods and decapods are different things. I haven't come across any pictures of decapods that are like my specimen, but on the other hand, isopods, as the name suggests, have lots of similar legs, growing from segments down most of the body's length, not just the front end. And typically, seven pairs of them.

[Yashca]

This looks to me to be the underside of a crab, the abdomen. After crabs die these often come off and wash up on the beach. This picture should help sum this up:

http://farm4.static.flickr.com/3126/...d45acb740a.jpg

[hatless]

You've got it, I think! Thanks.

[zan]

of course they aren't decapods... Doh!! Sorry, my mistake there!

The crab abdomen looks like the better suggestion of the 2.

Zan

[tom00_uk]

female spider crab i would go for

[tecdave]

Not really broad/wide enough for a female spider, they cover almost the entire thoracic sternum out to the leg sockets.
Dave