Creepy-crawly mounted sink in residence (6)
I believe the answer is:
spider
'creepy-crawly' is the definition.
(spider is a kind of invertebrate)
'mounted sink in residence' is the wordplay.
'mounted' says the letters should be written in reverse.
'sink' becomes 'dip' (synonyms).
'in' indicates putting letters inside.
'residence' becomes 'res'.
'dip' inserted inside 'res' is 'redips'.
'redips' in reverse letter order is 'SPIDER'.
(Other definitions for spider that I've seen before include "Predatory arachnid" , "Miss Muffet frightener?" , "Creepy-crawly" , "Snooker player's rest; eight-legged creature" , "Prised out the insect" .)