Sea creature (Thin Ice)

A creature which resembled a giant fish was imprisonned under the river Thames until 1814. (Thin ice)

Biology
The creature was massive in size, easily several times the size of a whale. It shared many similarities with lure fish, namely the overall shape of its body, its fins and its bioluminescent lure on its forehead. The creature was female and could produce several offspring who were the size of regular lure fish.

The creature's race were extremely long-lived and could potentially live for centuries, perhaps even millennia.

The Twelfth Doctor affirmed they were of terrestrial origin, perhaps from Earth's prehistoric era like the Silurians and the Sea Devils.