Motile and often predaceous they appear in the Cambrian but are not abundant until the Late Paleozoic. Early Paleozoic echinoderms were sessile stalked organisms such as crinoids , blastoids and cystoids . These became extinct replaced by more motile forms. Usually preserved as a carbon film, graptolites were thought to be extinct since Late Paleozoic but recently an organism was found that is believed to be a graptolite. Very useful as guide fossils but geologists not quite sure what conodonts were or if they were actually part of another larger organism.
Most accepted idea is that they belong to a chordate, perhaps some sort of jawless fish.
All chordates have a central hollow nerve chord or notochord, pharyngeal slits in the embryo and an internal skeleton. The first chordate, Pikaia, appeared in the Cambrian and resembled an eel. There are many classes of vertebrates. Paleozoic fossils contain a record of fish evolution. Agnatha first appear in the Ordovician.