Hemichordate

A marine invertebrate in the phylum Hemichordata, including acorn worms and pterobranchs. Hemichordates are deuterostomes whose body plan includes a proboscis, collar, and trunk.

Hemichordata: A phylum of marine deuterostome animals that includes acorn worms and pterobranchs. This broader taxon contains every hemichordate.
Deposit feeding: Feeding by ingesting sediment and digesting its organic material. Many acorn worms extract food while taking sediment into the mouth.
Acorn worm: A worm-shaped, usually solitary hemichordate in the class Enteropneusta. Acorn worms are the familiar burrowing form of the phylum.
Cambrian explosion: A geologically brief interval when animal diversity and fossil evidence expanded markedly, beginning about 539 million years ago. Early fossils assigned to hemichordate relatives occur in Cambrian seas.
Echinoderm: A marine invertebrate in the phylum Echinodermata, including sea stars and sea urchins. Echinoderms are hemichordates' sister group within Ambulacraria.
Deuterostome: An animal whose embryonic development typically forms the anus before the mouth. Hemichordates belong to this major branch of bilaterian animals.
Filter feeding: Feeding by straining suspended particles from water. Pterobranchs capture food particles with tentacled arms rather than ingesting sediment.
Pterobranch: A small, tube-dwelling hemichordate, often living in colonies and feeding with tentacled arms. Pterobranchs represent the other major living hemichordate body plan.
Graptolite: An extinct colonial marine animal, many forms of which belong to the pterobranch lineage. Graptolite fossils connect living pterobranchs with a diverse ancient record.
Cephalochordate: A small marine chordate, such as a lancelet, that retains a notochord throughout life. Cephalochordates possess a true notochord, unlike hemichordates.

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