Bryozoa
Colonial filter-feeders with a lophophore, known since the early Cambrian.
Bryozoa, also known as Polyzoa, Ectoprocta, or moss animals, are a phylum of simple, aquatic invertebrate animals that nearly all live in sedentary colonies. Typically about 0.5 millimeters long, they have a special feeding structure called a lophophore, a crown of tentacles used for filter feeding. Bryozoans are significant for their colonial nature, diverse zooid functions, and evolutionary history dating to the early Cambrian.
- phylum
- Bryozoa
- common_names
- Moss animals, Polyzoa, Ectoprocta
- typical_zooid_size
- 0.5 mm
- feeding_structure
- Lophophore
- habitat
- Aquatic, mostly marine, some freshwater
- earliest_fossils
- Early Cambrian
Lore & Background
Bryozoans form colonies of genetically identical zooids, each about 0.5 mm long, with a body divided into a cystid (body wall and exoskeleton) and a polypide (organs). Autozooids handle feeding, excretion, and nutrient supply, while some classes have specialist zooids for defense, reproduction, or attachment. The gut is U-shaped, with the mouth inside the tentacle crown and the anus outside. Zooids have no special excretory organs; waste-laden polypides are scrapped and replaced. Freshwater species are simultaneous hermaphrodites, while many marine species function first as males then females. Sperm is emitted into the water; some species release ova, others capture sperm via tentacles for internal fertilization. Larvae either have large yolks and settle quickly or swim and feed for days before metamorphosis. Freshwater species also produce dormant statoblasts.
Reader's Guide
Bryozoans are significant as a phylum of colonial aquatic invertebrates with a long fossil record beginning in the early Cambrian. Their colonies exhibit a wide range of forms—fans, bushes, sheets—and include specialized zooids for feeding, defense, and reproduction, with Cheilostomata being the most diverse order due to its variety of specialist zooids. They play ecological roles as prey for sea slugs, fish, sea urchins, and other predators, and as invasive species, such as Membranipora membranacea, which has reduced kelp forests off US coasts. Bryozoans have also spread diseases to fish farms. Chemically, extracts from one marine species have been investigated for cancer and Alzheimer's treatment, though results have not been encouraging. Their evolutionary relationships remain uncertain; scientists disagree on whether bryozoans are monophyletic, how they relate to entoprocts, and whether they belong with brachiopods and phoronids in Lophophorata or are protostomes or deuterostomes.
Did You Know?
- Five genera of bryozoans are solitary: Aethozooides, Aethozoon, Franzenella, Solella, and Monobryozoon.
- Freshwater bryozoans produce statoblasts that can survive conditions that kill the mother colony.
Frequently Asked Questions
What are Bryozoa?
Bryozoa is a phylum of tiny aquatic invertebrates—often nicknamed moss animals, Polyzoa, or Ectoprocta—that build sedentary colonies and capture food with a distinctive tentacled crown called a lophophore.
How do Bryozoa feed?
Each individual zooid extends its lophophore, a ring of ciliated tentacles, into the surrounding water to trap and sweep in microscopic particles and plankton.
How big is a single Bryozoan zooid?
Most zooids measure only about half a millimeter in length, which is why an entire colony can look like a fuzzy patch of moss on a rock even though it is made up of thousands of separate animals.
Where do Bryozoa live?
The overwhelming majority are marine species attached to hard substrates, though a smaller group has adapted to freshwater habitats; in both cases they remain sedentary colonial organisms.
How long have Bryozoa been around?
Their fossil record reaches back to the early Cambrian period, making them one of the oldest animal phyla still represented on Earth today.
More in Invertebrates 1-24
Elsewhere in the Invertebrates universe
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record