n. plHolothurioidea(Zoöl) One of the classes of echinoderms.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 HolothuridaHolothuridea, and Holothuroidea.
Century Dictionary and Cyclopedia
holothurioideaA class, order, or other group of Echinodermata; the sea-slugs, sea-cucumbers, or trepangs. They have an elongate, vermiform shape, and display little tendency to radiation in structure except at the oral end. They have a tough leathery integument instead of a hard calcareous test as in other echinoderms (though the skin may include hard spicules of various shapes), an oral circlet of tentacles, and a calcareous ring of several pieces round the mouth. There are two types of Holothurioidea, represented respectively by the genera Synapta and Holothuria, and forming two orders. The former, known as Apoda, Apodia, Apneumona, are hermaphrodite, with a reduced water-vascular system, no special respiratory apparatus, and no Cuvierian organs. The latter, called Pedata, Dipneumona, or Pneumonophora, have the sexes distinct, a respiratory tree, Cuvierian organs, and a developed water-vascular system including ambulacral feet. Also Holothuroidea and several other forms.
Webster's Revised Unabridged Dictionary
NL. See Holothure, and -oid
Before these changes were complete the Holothurioidea must have diverged, by the assumption of a crawling existence.
"Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 10" by Various