Bilateria () is a large clade or infrakingdom of animals called bilaterians (), characterised by bilateral symmetry (i.e. having a left and a right side that are mirror images of each other) during embryonic development. This means their body plans are laid around a longitudinal axis (rostral–caudal axis) with a front (or "head") and a rear (or "tail") end, as well as a left–right–symmetrical belly (ventral) and back (dorsal) surface. Nearly all bilaterians maintain a bilaterally symmetrical body as adults; the most notable exception is the echinoderms, which have pentaradial symmetry as adults, but are only bilaterally symmetrical as an embryo. Cephalization is a characteristic feature among most bilaterians, where the special sense organs and central nerve ganglia become concentrated at the front end.
Bilateria () is a large clade or infrakingdom of animals called bilaterians () characterised by bilateral symmetry (ie having a left and a right side that are mirror images of each other) during embryonic development This means their body plans are laid around a longitudinal axis (rostral–caudal axis) with a front (or "head") and a rear (or "tail") end as well as a left–right–symmetrical belly (ventral) and back (dorsal) surface Nearly all bilaterians maintain a bilaterally symmetrical body as adults; the most notable exception is the echinoderms which have pentaradial symmetry as adults but are only bilaterally symmetrical as an embryo Cephalization is a characteristic feature among most bilaterians where the special sense organs and central nerve ganglia become concentrated at the front end