'acephalan' originates from Greek, specifically the word 'akephalos,' where 'a-' meant 'without' and 'kephale' meant 'head.'

'akephalos' transformed into the Latin word 'acephalus,' and eventually became the modern English word 'acephalan.'

Initially, it meant 'without a head,' but over time it evolved into its current meaning of 'a headless mollusk.'