Andrew Kevin Walker was born on August 14, 1964.
Hemichordata is a phylum of marine deuterostome animals , generally considered the sister group of the echinoderms .. phylum. Phylum ( biology ). deuterostome. deuterostome. They appear in the Lower or Middle Cambrian and include two main classes  : Enteropneusta -LRB- acorn worms -RRB- , and Pterobranchia .. Cambrian. Cambrian. Enteropneusta. Enteropneusta. Pterobranchia. Pterobranchia. A third class , Planctosphaeroidea , is known only from the larva of a single species , Planctosphaera pelagica .. Planctosphaera pelagica. Planctosphaera pelagica. The extinct class Graptolithina is closely related to the pterobranchs .. Graptolithina. Graptolithina. Acorn worms are solitary worm-shaped organisms .. They generally live in burrows -LRB- the earliest secreted tubes -RRB- and are deposit feeders , but some species are pharyngeal filter feeders , while the family Torquaratoridae are free living detritivores .. Torquaratoridae. Torquaratoridae. Many are well known for their production and accumulation of various halogenated phenols and pyrroles .. Pterobranchs are filter-feeders , mostly colonial , living in a collagenous tubular structure called a coenecium .