Halecium muricatum, commonly known as the sea hedgehog hydroid,[2] is a species of hydrozoan in the family Haleciidae.

It occurs mainly in arctic and northern temperate waters, in both the Atlantic and Pacific Oceans.

Gonothecae (reproductive structures) develop on the stem and main branches; both male and female gonathecae are ovate and covered with rows of spines and appear identical.

In America its range extends southwards to Cape Hatteras and it is also present in Alaska and in the seas around Siberia.

[5] This hydrozoan is predated by the nudibranch Zelentia pustulata, which feeds almost exclusively on it, and winds its egg coils around its branches.