Cephalopods (9)
I believe the answer is:
octopuses
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cephalopods</span>' is the definition.<br/ ><span class="explanation-format__explanation">(octopus is a kind of cephalopod)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for octopuses that I've seen before include "With eight long tentacles, they live in the deep" , "Multi-armed sea creatures" , "Sea-creatures with eight tentacles" , "Sea molluscs with eight arms" , "Eight-armed cephalopods" .)