Wednesday, November 16, 2011

A Mystery Decapod

The Senda Darwin (Darwin’s trail) center lies up a hill and separated from the road by a river, over which there is a quaint little bridge that often has Ringed Kingfishers on it and Cincloides picking at the banks. On hot days, the water is tolerable so I walk down it sometimes and look for dragonflies, birds and whatever else is around (I found a dead lamprey today!).

The first time I did this, I noticed what I thought were little crabs. So I picked one up and lo and behold – the mutant offspring of a crab and a crayfish. I tried googling “Patagonian flat crayfish” which was incredibly uninformative, but eventually I figured it out. It is a member of the genus Aegla, which are related to the hermit crabs, and are their own family. Apparently, they are pretty much restricted to southern South America.  

They seem to be scavengers (one was eating the dead lamprey) and mostly just sit motionless on the bottom of the stream. Once you get the knack of what they look like, they are seemingly everywhere – a few per square meter. The lineage is ancient (70+ million years old) and there are fossils from marine environments, suggesting they might have evolved there, then moved into freshwater after which the marine forms died out. 

A fascinating little creature that only a week ago, I did not know existed!

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