Crossword puzzle clue "invertebrate's lack"

any member of the Arachnida, the large class of arthropods that includes spiders, scorpions, mites, etc.

the common worm

a word loosely used for a small invertebrate creature, esp. one with a body divided into sections; in zoological terms, a member of the Insecta

(Latin) an animal belonging to a large phylum of invertebrates that includes snails, shellfish etc., also MOLLUSK