Which extinct echinoderms lacked five-part body symmetry?

Extinct echinoderms that lacked five-part (pentamerous) body symmetry are primarily found within the subphylum Homalozoa, commonly known as carpoids.1

These organisms, which existed from the Middle Cambrian to the Middle Devonian, were characterized by a fundamentally asymmetrical, flattened body. The subphylum includes several extinct classes that lacked the radial symmetry typical of other echinoderms:1

• Class Stylophora: Distinguished by a unique single feeding arm that is sometimes interpreted as a stem.1
• Class Homostelea: Lacked a feeding arm but possessed a stem composed of two series of plates.1
• Class Homoiostelea: Featured a feeding arm and a complex stem made of more than two series of plates.1
• Class Ctenocystoidea: Lacked both a feeding arm and a stem, instead utilizing a unique feeding apparatus consisting of a grill-like array of movable plates around the mouth.1

Additionally, other early echinoderms were known to exhibit either no symmetry or bilateral symmetry before the development of radial pentamerous symmetry became widespread in the phylum.2