What does cephalous mean?
Cephalous is a technical adjective meaning 'having a head'. It is used chiefly in zoology and comparative anatomy to describe animals or life stages that possess a distinct, well-formed head region, often in explicit contrast with 'acephalous' creatures that lack one. A cephalous larva, for example, shows clear differentiation of a head end bearing sensory organs, whereas a headless form does not. The word derives from the Greek kephalē, meaning 'head' — the same root that gives us cephalopod (the squid-and-octopus class whose name literally means 'head-foot') and encephalitis ('inflammation within the head'). Because it belongs to the specialized vocabulary of biology rather than general usage, cephalous appears mainly in textbooks, taxonomic descriptions, and scholarly papers, where precision about body-plan features matters. Its value lies in allowing scientists a compact, unambiguous way to classify organisms by one of the most fundamental features of animal architecture: whether there is a head at all.
adjectiveHaving a head or heads; in biology, describing organisms or body parts that possess a distinct head region.
- Bearing a head or heads; having a well-defined head region (used especially in zoology to distinguish headed from headless forms).
"The cephalous larvae could be readily distinguished from their headless counterparts under the microscope."
"Among the flatworms, some species are distinctly cephalous while others lack any recognizable head."
"Early taxonomists divided the group into cephalous and acephalous categories based on head structure."
In zoology, whether an animal counts as 'cephalous' can literally decide its branch on the tree of life — the entire phylum Mollusca gets sorted by who has a head and who doesn't.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cephalous
Cephalous comes from the Greek kephalē, meaning 'head', combined with the adjectival suffix -ous. It entered scientific English through Latinized Greek forms during the development of modern zoological terminology, alongside a large family of 'cephalo-' words such as cephalopod, encephalon, and hydrocephalus. Its closest working partner in biological texts is the negated form acephalous ('headless'), which shares the same root.
How cephalous is actually used
A technical term used almost exclusively in zoology and comparative anatomy, typically in formal scientific writing. It frequently appears paired with its antonym 'acephalous'. Rare in everyday English.
Easily confused with cephalous
Cephalic means 'relating to the head', while cephalous specifically describes something as actually possessing a head.