272 PHYLUM ECHINODERMA. 
some others the body cavity serves as a brood-pouch. This 
illustrates how the same result may be reached in a great 
variety of ways. 
The calcareous plates of Holothurians are found as far 
back as Carboniferous strata. 
As “trepang” or “béche-de-mer,” the Holothurians of 
the Pacific form an important article of commerce, being 
regarded as a delicacy by the Chinese. 
Classification.— 
Order 1. Actinopoda. The radial water vessels are associated with 
external tentacles, tube-feet, and ambulacral papilla, but the 
tube-feet and papilla may be absent. There are several 
families, e.g. the deep-sea Elasipoda, markedly bilateral, almost 
always flattened ventrally, often with an external pore for the 
stone canal, e.g. Hipzdia and Kolga; the Aspidochirote, e.g. 
Holothuria and Stzchopus, and Dendrochirote, e.g. Cucumaria, 
Thyone, Psolus, with tube-feet as well as tentacles; the Molpa- 
diidze with tentacles only, eg. Molpadia; the Pelagothuriidze 
containing the free-swimming Pelagothuria. 
Order 2. Paractinopoda or Apoda. The only external outgrowths ot 
the water-vascular system are the pinnate tentacles around the 
mouth. One family, Synaptide, e.g. Syzapta and Chzridota. 
There are no tube-feet or respiratory trees or Cuvierian organs. 
The calcareous bodies are usually beautiful anchors and plates. 
Many are hermaphrodite. 
Class Crinoipea. Feather-stars 
Usually stalked forms, with five jointed, often branched 
arms (“brachia”), growing out from a central cup or 
“theca,” and bearing pinnules; the arms arise from a 
‘orresponding number of thecal plates or “radials,” below 
which there is a circlet of alternating “‘basals,” often with 
“infra-basals” alternating again with them; below the 
“Bbasals” or “infra-basals” there is usually a jointed stem 
anchored to the substratum by “ cirri.” 
The feather-stars or sea-lilies differ from other Echino- 
derms in being fixed permanently or temporarily by a jointed 
stalk. The modern Comatulids, eg. the rosy feather-star 
(Comatula or Antedon rosacea) leave their stalk at a certain 
stage in life; but the other Crinoids, e.g. Pentacrinus, are 
permanently stalked, like almost all the extinct stone-lilies 
or encrinites, once so abundant. Most of them live in deep 
