[CHAPTER IX.]
FOSSIL WORMS, SEA-MATS and LAMP-SHELLS.
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The first-named group, the ringed worms, belong to the phylum Annelida, so-called because of the ring-like structure of their bodies. The two remaining groups, the Polyzoa or Sea-mats and the Brachiopods or Lamp-shells, are comprised in the phylum Molluscoidea, or mollusc-like animals.
WORMS (Annelida).
Annelida and their Fossil Representatives.—
These animals, owing to the scarcity of hard parts within their bodies, play a rather insignificant role as a fossil group. Worms are laterally symmetrical animals, with a dorsal and a ventral surface. They are segmented, the body being formed of numerous rings. Only those of the Class Chaetopoda (“bristle-feet”) are represented by identifiable fossil remains. Fossil worms, moreover, chiefly belong to the Order Polychaeta (“many bristles”). The horny jaws of these worms are sometimes found in the older rocks and are known as conodonts.