Rock pool find

Rock pool find

Observation - Rock pool find. Description: Whilst looking in rock pools at Whitby in March found this unusual creature which looked like at eel but is very flat in appearance when out of water. Not the best of photos but can anyone help identify it for me please. Thankyou.

Whilst looking in rock pools at Whitby in March found this unusual creature which looked like at eel but is very flat in appearance when out of water. Not the best of photos but can anyone help identify it for me please. Thankyou.