\Hol`o*thu`ri*oi"de*a\, n. pl. [NL. See
{Holothure}, and {-oid}.] (Zo["o]l.)
One of the classes of echinoderms.
Note: They have a more or less elongated body, often
      flattened beneath, and a circle of tentacles, which are
      usually much branched, surrounding the mouth; the skin
      is more or less flexible, and usually contains
      calcareous plates of various characteristic forms,
      sometimes becoming large and scalelike. Most of the
      species have five bands (ambulacra) of sucker-bearing
      feet along the sides; in others these are lacking. In
      one group (Pneumonophora) two branching internal gills
      are developed; in another (Apneumona) these are
      wanting. Called also {Holothurida}, {Holothuridea}, and
      {Holothuroidea}.