Pterobranchs

Pterobranchs are small, colonial marine hemichordates comprising the class Pterobranchia. They live in secreted tubes on the seabed and consist of many individual zooids linked by stolons forming a shared coenecium.

Each zooid has a compact body with a feeding apparatus composed of a crown of ciliated tentacles that filters particles from seawater. Water flow is driven by ciliary action, and the tentacular crown can be retracted for protection.

Reproduction occurs sexually and asexually. In many species, fertilization produces free-swimming tornaria-like larvae; in many pterobranchs, colonies can propagate asexually by budding from the stolons or zooids, leading to new zooids within the same coenecium.

Distribution and ecology: Pterobranchs are cosmopolitan marine animals, most diverse in cold, deep-sea environments, but also found in shallow coastal waters. They typically inhabit sediments or hard substrates where the tubes anchor and extend feeding structures into the water column.

Fossils and systematics: They are deuterostomes related to echinoderms and enteropneusts; extant groups include Cephalodiscus and Rhabdopleura, which form colonies in tubes. The extinct graptolites are commonly regarded as pterobranchs and constitute an important deep-time fossil record.