Creepy-crawly (6)
I believe the answer is:
insect
'creepy-crawly' is the definition.
(insect is a kind of invertebrate)
This is all the clue.
(Other definitions for insect that I've seen before include "Contemptible type" , "E.g. cricket" , "may be attracted to a website?" , "cricket, say" , "Small arthropod creature" .)