Phylum Hemichordata

A varied but small group, probably related to the Chordata, but without a notochord.

class ENTEROPNEUSTA (Present)

Worm-like animals with no external skeleton.

class PTEROBRANCHIA (Ordovician to Present)

Fixed colonial organisms. Skeleton of protein. Lophophore attached by a stalk to an internal protein tube (the stolon).

class GRAPTOLITHINA (Cambrian to Carboniferous) Colonial marine animals with a skeleton of protein.

order Dendroidea (Cambrian to Carboniferous)

Graptolites with a protein stolon, include benthic and pelagic forms.

order Graptolidea (Ordovician to Lower Devonian)

Graptolites with no preserved stolon; probably all pelagic.

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