Acephala
/(ˌ)eɪˈsɛfələ/ /(ˌ)eɪˈsɛf(ə)lə/ /(ˌ)eɪˈkɛfələ/Zoology. Now historical
noun
Treated as plural. A former class of invertebrates lacking distinct heads, broadly equivalent to Bivalvia (bivalve molluscs) but also including tunicates; (also in form acephala) invertebrates of this class collectively. Occasionally with singular concord (also in form acephala): an invertebrate of this class.
Origin
Early 19th century. From scientific Latin Acephala, plural noun, use as noun of post-classical Latin acephalus, after French acéphales, plural noun; compare scientific Latin -a.