The Collaborative International Dictionary of English v.0.48:

Echinodermata \E*chi`no*der"ma*ta\
   ([-e]*k[imac]`n[-o]*d[~e]r"m[.a]*t[.a]), n. pl. [NL., fr. Gr.
   'echi^nos hedgehog, sea urchin + de`rma, -atos, skin.]
   (Zo["o]l.)
   One of the grand divisions of the animal kingdom. By many
   writers it was formerly included in the Radiata. [Written
   also Echinoderma.]
   [1913 Webster]

   Note: The species usually have an exterior calcareous
         skeleton, or shell, made of many pieces, and often
         covered with spines, to which the name. They may be
         star-shaped, cylindrical, disk-shaped, or more or less
         spherical. The body consists of several similar parts
         (spheromeres) repeated symmetrically around a central
         axis, at one end of which the mouth is situated. They
         generally have suckers for locomotion. The group
         includes the following classes: Crinoidea, Asterioidea,
         Ophiuroidea, Echinoidea, and Holothurioidea. See these
         words in the Vocabulary, and also Ambulacrum.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Echinodermata
    n 1: radially symmetrical marine invertebrates including e.g.
         starfish and sea urchins and sea cucumbers [syn:
         Echinodermata, phylum Echinodermata]