Sounds like:
(and probably came in on a plant)

Water louse

The water louse, or water slater, has a flattened body and looks similar to
their close relation, the terrestrial woodlouse. They are bottom dwellers,
crawling through and feeding on the detritus and debris that collects there.
The parallels with the woodlouse are strong as it favours the dead leaves that
gather in stagnant or slow-moving water. They are up to 15mm long,
greyish-brown in colour and are unable to swim freely. The male is much larger
and often carries the female about clasped to his front. The body is made up of
seven distinct segments, each with a fairly unspecialised pair of appendages,
although the front pair are more adapted for grasping. They are undoubtedly
primitive creatures but play an important role in the bog pool ecosystem as a
food source for the many predators that live there.


kathy :-)
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