Bryozoans are tiny colonial organisms characterized by the presence of a tentacled feeding structure called a lophophore that filters food particles out of the sea water and transfers them to the mouth. The tentacles of Bryozoans differ from those of anemones and corals in that they contain a body cavity and the anus is located outside the circle of lophophore tentacles. Encrusting Bryozoans in the Gulf of Maine include the cosmopolitan Membranipora membranacea and the native Electra pilosa. Encrusting colonies have a lacy appearance and are typically found on brown algae such as Laminaria species but are also found on red algae and solid flat surfaces in marinas.
Membranipora forms mat-like calcareous colonies of small, closely packed zooids living inside a rectangular sheath that secretes a protective, calcified enclosure. Each rectangular compartment is composed of lateral calcified walls and ventral uncalcified bands, which provide flexibility. A membrane completely roofs the space between the supporting side walls. The enclosure has an orifice through which the lophophore extends into the water column for feeding. In Membranipora, the orifice is covered by an operculum.
Membranipora forms mat-like calcareous colonies of small, closely packed zooids living inside a rectangular sheath that secretes a protective, calcified enclosure. Each rectangular compartment is composed of lateral calcified walls and ventral uncalcified bands, which provide flexibility. A membrane completely roofs the space between the supporting side walls. The enclosure has an orifice through which the lophophore extends into the water column for feeding. In Membranipora, the orifice is covered by an operculum.
Membranipora membranacea Growing on a Blade of Laminaria
A small colony of Membranipora membranacea growing on a blade of the brown algae Laminaria longicruris collected from Beverly Marina The point of origin (the ancestrula) is in the upper left quadrant. Membranipora is characterize by rectangular enclosures and a smooth edge lacking zooids along the growing colony edge. 1x zoom x 10x objective.
Smooth Growth Zone at the Edge of Membranipora membranacea Colony
Growing edge of Membranipora membranacea lacks zooids and provides a smooth edge for excurrent water flow away from the colony. 1.5x zoom x 10x objective.
Diagram of an Encrusting Bryozoan: Retracted (left) and Feeding (right)
Diagram of two encrusting zooids, one retracted and one with the lophophore extended. The lophophore circulates water through the tentacles, filters food particles, and transfers them by ciliary motion to the mouth. Because the zooids are closely packed, the lophophores of the colony work cooperatively to circulate water through tentacles and to remove waste and unwanted particles. When disturbed, the retractor muscles pull the zooid and lophophore into the safety of the enclosure. From www.earthlife.net - bryozoa.
Membranipora membranacea Rectangular Zooid Chambers
Calcified rectangular walls of the colony of Membranipora membranacea. The units are arrange in staggered rows that give the structure additional strength. Short tubercles (spines) occur at the corners of the rectangular enclosures, 6 spines per enclosure. 4x zoom x 10x objective.
Beyond the Human Eye
WoRMS: Membranipora membranacea
Web Photo, showing Colony Enclosures by Scanning Electron Microscopy:
Membranipora organization by SEM Dennis Gordon
Web Photo Favorites, showing colony formation:
Lovell and Libby Lanstroth, California Academy of Science
Ann-Margret Amui-Vedel's Webpage, NUI Galway
Ann-Margret Amui-Vedel's Webpage, NUI Galway
Twin Ancestrula Marney Pratt
Emerging Colony Lovell and Libby Lanstroth Collection, CalPhotos
Small Colony Marney Pratt
Colony in Culture showing lophophores Ann-Margret Amui-Vedel
1. Pratt, MC. Effect of zooid spacing on bryozoan feeding success: is competition or facilitation more important? Biol. Bull. 207:17-27, 1004.
2. Pratt, MC. Consequences of coloniality: influence of colony form and size on feeding success in the bryozoan Membranipora membrancea. Mar. Ecol. Prog. Ser. 303: 153-165, 2005.
3. Von Dassow, M. Effects of ambient flow and Injury on the morphology of a fluid transport system in a Bryozoan. Biol. Bull 208:47-59, 2005.
3. Winston, JE. Current related morphology and behavior in some Pacific coast Bryozoans. In Advances in Bryozoology: Proceedings of the 4th International Conference on Bryozoa, GP Larwood & MB Abbott, eds. Systematics Association Special Volume, 13:, 247-268, 1979.
