The Collaborative International Dictionary of English v.0.48:

Isopleura \I`so*pleu"ra\, n. pl. [NL. See Iso-, and Pleura.]
   (Zool.)
   A subclass of Gastropoda, in which the body is symmetrical,
   the right and left sides being equal.
   [1913 Webster]

   Note: The intestine terminates at the posterior end of the
         body, and the gills and circulatory and reproductive
         organs are paired. It includes the chitons
         (Polyplacophora), together with Neomenia and
         Ch[ae]toderma, which are wormlike forms without a
         shell.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Placophora \Pla*coph"o*ra\ (pl[.a]*k[o^]f"[-o]*r[.a]), n. pl.
   [NL., from Gr. pla`x, plako`s, tablet + fe`rein to bear.]
   (Zool.)
   A division of gastropod Mollusca, including the chitons. The
   back is covered by eight shelly plates. Called also
   Polyplacophora. See Illust. under Chiton, and
   Isopleura.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Polyplacophora \Pol`y*pla*coph"o*ra\, n. pl. [NL. See Poly-,
   and Placophora.] (Zool.)
   See Placophora.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Polyplacophora
    n 1: small class of marine mollusks comprising the chitons;
         sometimes considered an order of the subclass Amphineura
         [syn: Polyplacophora, class Polyplacophora]