Bryozoan Fossils

Victorian Marine Fossils series

What are bryozoans?

Bryozoans are a group of mostly marine creatures living in colonies made up of hundreds of tiny individual animals. The skeletons of the colonies, usually composed of calcium carbonate, may have a stick-like, frond-like, net-like or mound-like shape, or may form an encrusting mat on shells, rocks, seaweed or jetty piles. Some bryozoans are commonly known as ‘lace corals’ because of their growth form, but they are not related to the true corals. The individual bryozoan animals live in tube-shaped or box-like compartments, usually no more than 1 mm in length, that are crowded together in the colony. These compartments have tiny openings through which the bryozoan animals extend their tentacles to filter food particles and oxygen from the seawater. In some bryozoans these openings can be closed off by a lid.


Fossil bryozoan, Selenaria cognata, showing the individual compartments of the colony and their openings; middle Miocene (c. 15 my old), Hamilton district, Victoria. Whole colony is about 3 mm in diameter (taken with scanning electron microscope).
Photographer / Source: Phil Bock, Honorary Researcher, Museum Victoria

The tentacles of bryozoans are part of a filtering structure called the lophophore. This structure is found also in another group of marine invertebrates, the brachiopods or lamp shells. Brachiopods are very different in appearance from bryozoans, being much larger, not living in colonies, and having a shell composed of two parts like a mussel. However, the presence of a lophophore in bryozoans and brachiopods indicates that both of these groups are related and evolved from a common ancestor.


Fossil bryozoan, Reteporella sp.; Late Oligocene (c. 25 my old), Point Addis, Victoria
Photographer: David Holloway, Museum Victoria

Bryozoans are very common in present-day seas but are unfamiliar to many people, because they mostly live below the low tide level, and when their skeletons are washed up onto the shore they are usually overlooked or confused with seaweed. About 6000 species of bryozoans are living at the present day but several times that number of fossil species have been described by palaeontologists.

The fossil history of bryozoans

Bryozoans first appeared in the early part of the Ordovician Period, about 470 million years ago (mya), and shortly afterwards evolved rapidly into many new forms. For the remainder of the Palaeozoic Era (until 251 mya) they were abundant in shallow marine environments and were an important component of coral reefs formed during this time. The massive extinctions in marine creatures at the end of the Palaeozoic greatly affected bryozoans, but during the following Mesozoic Era (251-65 mya) they recovered and new major groups appeared, including those groups that are most common today. During the Cainozoic Era (less than 65 mya) bryozoans continued to increase in variety.


Fossil bryozoan, Fenestella margaritifera; Early Devonian (c. 400 my old), Lilydale district, Victoria
Photographer: David Holloway, Museum Victoria

Where are fossil bryozoans found in Victoria?

Bryozoans occur widely in central and eastern Victoria in sedimentary rocks deposited during the Silurian and Early Devonian periods (434-384 mya), notably in the Heathcote, Lilydale, Kinglake, Mansfield, Walhalla, Tyers, Tabberabbera and Omeo districts. Fossil bryozoans are most abundant, however, in clays, sands and limestones of Cainozoic age (less than 65 my old) that occur mainly along the southern coast, some limestones of this age being made up almost entirely of their fossilized skeletons. Much of the recent sediment of Bass Strait is also made up of fragments of dead bryozoan colonies, and of fossil bryozoans eroded from older deposits.


Fossil bryozoan, Aspidostoma sp; middle Miocene (c. 12 my old), Bairnsdale district, Victoria
Photographer: David Holloway, Museum Victoria

Visitor Information

Common species of bryozoans from Victoria are exhibited in the Marine Invertebrate Fossil Drawers in the Discovery Centre at the Melbourne Museum.

Further Reading

Edgar, G. J. 1997. Australian marine life. Reed Books, Kew, Victoria. [Photographs of living species of bryozoans from southern Australia.]

McKinney, F. K. & Jackson, J. B. C 1989. Bryozoan evolution. Unwin Hyman, Boston. [Contains a detailed account of bryozoan classification and evolution.]

Comments (4)

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destiny 20 December, 2011 08:38
good and great information
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Eric 30 October, 2012 02:38
grat info loveit
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Sarah Bardot 25 February, 2014 16:18
What did they eat?
Discovery Centre 1 March, 2014 16:08

Hi Sarah, Bryozoans are suspension feeders using lophophores – structures that can filter small particles in the water column and direct them toward the mouth of the Bryozoan.  Bryozoans are detritovores (feed on detritous in the water column).   They feed on algae and very small particles of abraided algae (including the bacteria that live on these abraided particles), plankton, flagellates (an organism with one or more whip-like structures (flagella)), diatoms and the spores of macroalgae.

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