Pterobranch
| Pterobranchia Temporal range: Cambrian stage 3–Recent |
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|---|---|
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| Cephalodiscus dodecalophus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Hemichordata |
| Class: |
Pterobranchia Lankester 1877 |
| Subgroups | |
Pterobranchia is a clade of small worm-shaped animals. They belong to the Hemichordata, and live in secreted tubes on the ocean floor. Pterobranchia feed by filtering plankton out of the water with the help of cilia attached to tentacles. There are about 30 known living species in the group.
The class Pterobranchia was established by Ray Lankester in 1877. It contained, at that time, the single genus Rhabdopleura. Rhabdopleura was at first regarded as an aberrant polyzoon, but when the Challenger report on Cephalodiscus was published in 1887, it became clear that Cephalodiscus, the second genus now included in the order, had affinities in the direction of the Enteropneusta.
Studies under an electron microscope have suggested that pterobranchs belong to the same clade as the extinct graptolites, and phylogenetic analysis suggests that the pterobranchs are living members of the graptolite clade.
Pterobranchs are small worm-like filter-feeders, living on the ocean floor, often in relatively deep waters. Like their relatives, the acorn worms, their body is divided into three parts: an anterior proboscis, a collar, and a trunk. The proboscis is wide and flattened at the tip, and in most species contains glands that secrete a tube of organic material in which the pterobranch spends its adult life. The animals are mostly colonial, with several zooids living together in a cluster of tubes. In some species, the individual zooids within the colony are connected by stolons. The genus Atubaria is unusual in lacking the tubes typical of other pterobranchs.
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