Leafy Green Bryozoan, Sessibugula translucens
Leafy Green Bryozoan, Sessibugula translucens. Underwater photograph taken in Bahía de La Ventana, La Paz, Baja California Sur, December 2025. Photograph courtesy of Aaron Woodrow, Juneau, Alaska. Identifications courtesy of Greg Timms, youtube.com/@CoralmasterdivesPuerto-Vallarta/videos. The Bryozoan is being preyed upon by a Blue-striped Tambja, Tambja eliora.
Phylogeny: The Leafy Green Bryozoan, Sessibugula translucens (Osburn, 1950), is a member of the Burulidae Family of Bryozoans. The Bugulidae Family has thirty-four genera and there is one species in the Sessibugula Genus. Sessibugula translucens serves as the type species for the genus Sessibugula. It is known in Mexico as Briozoo de Hojas Verdes and Briozoo Verde Frondoso. Bryozoans are aquatic colonial invertebrates composed of individual interconnected units called zooids. Each zooid functions as a distinct organism contributing to the feeding, growth, and structural integrity of the colony.
Morphology: The Leafy Green Bryozoan is an aquatic colonial invertebrate composed of individual interconnected units called zooids. Each zooid functions as a distinct organism contributing to the feeding, growth and structural integrity of each colony. The colonies vary in size and can be very large. Sessibugula translucens forms thin, encrusting colonies on smooth surfaces. The structural matrix forms a flat layer that lacks open spaces (fenestrae). Individual zooids measure between 0.65 and 0.95 mm in length and 0.30 to 0.45 mm in width. Each zooid features an irregularly oval or elliptical frontal opening (opesia) occupying approximately the distal half of its frontal surface. Skeletal walls are thin, making boundaries between adjoining zooids difficult to distinguish under standard magnification. The original taxonomic descriptions characterize the species as green or transparent, however live colonies in the Mexican Pacific—including Bahía de Banderas and the Sea of Cortez—have been observed in both blue and green variations. The colonial structure remains thin and translucent across all color morphs. They have large lettuce-like leaves extending upward from the base that is attached to the substrate. The morphometrics of the Leafy Gren Bryozoan are poorly documented in the scientific literature.
Habitat and Distribution: The Leafy Green Bryozoan is a sessile marine species that is fairly common a colonial species found in small formations that attach to marine substrate that inhabit the intertidal and shallow subtidal zones. They are not mobile. The Leafy Green Bryozoan is native to the Eastern Pacific Ocean with published records documenting the geographic distribution in the Sea of Cortez of California, Costa Rica, and the Galápagos Islands, with additional records from Bahía de Banderas, Jalisco and Guerrero, Mexico. They are found at depths between 9 m (30 feet) and 108 meters (354 feet).
Diet: The Leafy Green Bryozoan is a suspension filter feeder that consumes plankton and organic detritus from the surrounding water. Each zooid utilizes a ciliated tentacular crown (lophophore) to generate localized currents that direct suspended microparticulates toward the mouth.
Predation: The Leafy Green Bryozoan is preyed upon by a series of nudibranchs and predominately by the Slimy Slug, Tambja abdere, that retain the the tambjamines they ingest and utilize as a defense against predation. They are also preyed upon by the sympatric nudibranch, the Blue-striped Tambja, Tambja eliora, that sequesters identical chemical compounds. In turn the Tiger Dorid or Sea Tiger Nudibranch, Tyrannodoris tigris, a carnivorous nudibranch preyes on both abdere and eliora, forming a specialized three-tiered trophic chain mediated by the bryozoan’s chemical output. When attacked by the Tiger Dorid, the Slimy Slug secretes a defensive mucus rich in concentrated tambjamines, causing the predator to abort the attack. Due to its smaller mass, the Blue-striped Tambja carries lower chemical concentrations and typically uses a physical swimming escape response rather than chemical deterrence. Controlled assays have demonstrated that chemical concentrations dictate Blue-striped Tambja behavior. Low chemical thresholds function as a feeding attractant toward the bryozoan, while elevated concentrations induce a repulsive deterrent response. These secondary metabolites function simultaneously as foraging cues and warning signals within this regional chemical ecosystem.
Reproduction: The Leafy Green Bryozoan reproduce sexually as hermaphrodites and asexually via budding. The individual zooids that make up the colony possess both males and female reproductive organs. Sperm is released into the water and caught by the tentacled feeding structures of neighboring zooids to fertilize the eggs. The fertilized eggs are retained by the females before they are released as free swimming larvae. These larvae eventually settle out on the bottom and attach to the hard bottom and transform into zooid and start new colonies. Reproduction via budding involves the generation of a new genetically identical zooid that grow directly from the existing ones. Or, a piece of colony can break off and the fragments grow into a new colony.
Ecosystem Interactions: The Leafy Green Bryozoan plays an essential role in the marine food web by synthesizing tambjamines (alkaloids A–D), which function as secondary chemical defenses. These compounds are then ingested by the grazing nudibranchs and are passed along to the apex predator, Roboastra tigris.
Human Interactions: The Leafy Green Bryozoan have no direct impact on human activities. From a conservation perspective the Leafy Green Bryozoan has not been formally evaluated. They are not suitable for aquarium use being not able to survive in captivity.
Synonym: None.