Aquatic invertebrate?

Aquatic invertebrate?

Observation - Aquatic invertebrate?. Description: Found in a pond. Placed on A4 lined paper; lines seen in photo for size comparison. Gap between lines is 8mm. Any help identifying this specimen would be greatly appreciated.

Found in a pond.
Placed on A4 lined paper; lines seen in photo for size comparison.
Gap between lines is 8mm. Any help identifying this specimen would be greatly appreciated.