Cephalodiscida

Cephalodiscida is an order of small, colonial marine hemichordates within the class Pterobranchia. They form colonies consisting of individual zooids housed in secreted tubes and linked by a network of stolons. Cephalodiscids are one of the two living pterobranch lineages, the other being Rhabdopleurida.

Each zooid bears a retractable feeding apparatus, typically a crown of ciliated tentacles surrounding the mouth, used to capture suspended food. Zooids are connected by stolons into a common colony, with some individuals specialized for defense or reproduction.

The life cycle includes a free-swimming larval stage that resembles tornaria, followed by asexual budding that expands the colony. Cephalodiscids are marine and occur worldwide, from shallow coastal zones to deeper waters, attaching to substrates such as rocks, shells, and algae.

The fossil record of pterobranchs is extensive through graptolites, and cephalodiscids help inform the early evolution of hemichordates and colonial life.