'non-annelid' originates from English, formed by the prefix 'non-' (from Latin 'non' meaning 'not') combined with 'annelid' (from New Latin 'Annelida'), where Latin 'anellus' meant 'little ring'.

'Annelid' comes from Latin 'anellus' (diminutive of 'annus'/'annulus' meaning 'ring'), passed into New Latin as 'Annelida' and then into English as 'annelid'; the English prefix 'non-' was then attached to form 'non-annelid'.

The element 'annelid' originally evoked 'little ring' (referring to ringed/segmented bodies) and came to denote segmented worms; adding 'non-' has the straightforward negative sense 'not an annelid', so the compound's meaning is a direct negation of the original biological category.