† monocoelianadj. [ < mono-comb. form + ancient Greek κοιλία (see cœlian.) + -ansuffix] ZoologyObsoleterare having a single undivided cerebral cavity; spec. of or relating to the former class Monocoelia (now the subphylum Cephalocordata) of lancelets; cf. monocelicadj.Apparently only attested in dictionaries or glossaries.
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1890 Cent. Dict.Monocœlian, having the encephalocœle single; specifically, of or pertaining to the Monocœlia.