Note: It includes those Invertebrata having the body composed
of a series of ringlike segments (arthromeres). By some
writers, the unsegmented worms (helminths) have also
been included; by others it is restricted to the
Arthropoda. It corresponds nearly with the Annulosa of
some authors. The chief subdivisions are Arthropoda
(Insects, Myriapoda, Malacopoda, Arachnida,
Pycnogonida, Crustacea); and Anarthropoda, including
the Annelida and allied forms.
2. One of the subdivisions of the Brachiopoda, including
those that have the shells united by a hinge.
3. A subdivision of the Crinoidea.