Lophophore

The lophophore is a feeding organ found in certain sessile aquatic invertebrates, notably brachiopods (lamp shells), bryozoans (ectoprocts), and phoronids. It consists of a circular or horseshoe-shaped crown of hollow, ciliated tentacles that surround the mouth. The tentacles are often richly lined with cilia and sometimes contain connective tissue and coelomic extensions, and they can be retracted into a protective body cavity or tube in many species.

Anatomy and variation: The lophophore’s shape and arrangement vary among the groups. Bryozoans typically have a circular crown with many tentacles that can protrude from an opening in the colony or individual zooid. Brachiopods display two symmetrical rows of tentacles within the shell valves, forming a distinctive U- or horseshoe-shaped crown. Phoronids possess a circular or horseshoe crown that sits inside a simple body tube. In all forms, the lophophore is generally supported by the body wall and connected to a coelomic canal system, and it is often capable of retraction for protection.

Function and ecology: The primary function of the lophophore is filter feeding. Ciliary action on the tentacles generates water currents that bring suspended particles toward the mouth, where mucus traps food, which is then transported to the digestive tract. The lophophore can also play a role in gas exchange for these animals. Most lophophorate species are sessile or slow-moving and obtain nutrients from marine waters; bryozoans are often colonial.

Evolution and classification: The lophophore has long served as a key diagnostic feature of lophophorates, a grouping that includes brachiopods, bryozoans, and phoronids. Molecular studies have complicated simple linear classifications, placing these groups within broader Lophotrochozoa while leaving the precise relationships among them debated. The lophophore remains an important example of a conserved feeding structure across diverse lineages.