Archiannelida

from WordNet (r) 3.0 (2006)

Archiannelida
    n 1: a class of Annelida [syn: {Archiannelida}, {class
         Archiannelida}]

from The Collaborative International Dictionary of English v.0.48

Archiannelida \Ar`chi*an*nel"i*da\, n. pl. [NL.; pref. archi- +
   annelida.] (Zool.)
   A group of Annelida remarkable for having no external
   segments or distinct ventral nerve ganglions.
   [1913 Webster]