Geology 1200      Lab #5

Bryozoa

[2] Membranipora membranacea

Bryozoans are sessile colonial animals. The individual bryozoan animal (or zooid) generally has a tubular or sac-like body that is housed in a chitinous or calcium carbonate exoskeletal case called a zooecium, which can be box-shaped or tube-shaped. The zooid protrudes through its zooecium through a single orifice to feed, using a ring of tentacles around the mouth called the lophophore (left). The orifice of the zooecium may or may not have an operculum, or hatch-like lid. A colony of more than one zooecium is called a zoarium. Zoaria may occur in the shape of mats, crusts, lobes, lumps, trees, or funnels up to several centimeters in size. There is a division of functions among the zooids in a zoarium, and the zooids are differentiated accordingly.

[5] A bryozoan limestone from South Australia

The chief distinguishing character of the bryozoa is their U-shaped digestive tract, with a mouth, esophagus, stomach, intestine, and anus. Bryozoans reproduce both sexually and asexually. A larva hatches from a fertilized egg and metamorphoses into the primary zooid, or ancestrula. The ancestrula then produces one or more further zooids by budding. In this manner, the zoarium is created. Bryozoans are mostly marine, but some species are estuarine or freshwater. Bryozoa are the most abundant fossils in many marine limestones, calcareous shales, and mudstones.

1. Fan or screen-like shape with tiny apertures.
2. Twig-like branches with tiny apertures.
3. Bulbous or encrusting masses with tiny apertures.
4. Fine, outward radiating striations on broken surface.
5. Screw-shaped twigs

1. COLONIAL CORALS are sometimes confused with bryozoa. Corals are, however, much larger animals and the skeletal opening in which they live ranges up to 1cm or more. Corals also possess distinctive septa not found in bryozoa.
2. STROMATOPOROID skeletons often appear superficially like massive bryozoan skeletons, but stromatoporoids have no apertures. Bryozoan skeletons, on a broken surface, have a pillar-like appearance of some stromatoporoids but never have laminae.