Graptolite
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Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle C
ROM28084 Didymograptus
Diversity of graptolite colony forms
A hypothetical graptolite zooid inside its theca, reconstructed based on living pterobranchs
Pendeograptus fruticosus from the Bendigonian Australian Stage (Lower Ordovician; 477–474 mya) near Bendigo, Victoria, Australia. There are two overlapping, three-stiped rhabdosomes.
Hemichordate
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Hemichordata is a phylum which consists of triploblastic, eucoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in
Graptolite
…resembling fossils' rather than true fossils, though later workers supposed them to be related to the hydrozoans; now they are widely recognized as hemichordates. The name "graptolite" originates from the genus Graptolithus ("writing on the rocks"), which was used by Linnaeus in 1735 for inorganic mineralizations…
Enteropneusta USNM 1431735, MBIO32531, BMOO 08254 Specimen Image
Cephalodiscus nigrescens
Schematic of embryonic cleavage and development in P. flava and S. kowalevskii
Amplexograptus, a graptolite hemichordate, from the Ordovician near Caney Springs, Tennessee.