bryozoanclass

BRYOZOANS

CLASSIFICATION

General Information

Division of bryozoan groups is based on surficial morphology, extra-zooidal structures, colonial growth habits, zooid morphology, presence of specialized zooids (e.g., maternal zooids), and internal structures of the zooecium. In order to help in identification, it may help to know that colonial bryozoans come in two basic types:

1. Those with tightly packed zooecia which share zooecium walls, they have multiple pores and a well defined mature and immature region such as in the trepostomes, cyclostomes, and the fenestrates.

2. Those with moderately to loosely packed zooecia usually encrusting one-zooecium-thick, and commonly with frontal walls as typified by the Cheilostomes

CLASSIFICATION AND GEOLOGIC RANGES

Phylum Bryozoa

Class Stenolaemata (Ordovician-Recent)

Order Trepostomata (Ordovician-Triassic)

Order Fenestrata (Ordovician-Permian)

Order Cyclostomata (Ordovician-Recent)

Class Gymnolaemata (Ordovician-Recent)

Order Cheilostomata (Jurassic-Recent)

Order TREPOSTOMATA

Trepostomes are characterized by long-curved zooecia separated by thin walls. Each zooecium has mature and immature regions. Apertures of autopores are typically polygonal. Trepostomes can be differentiated from similar-looking cryptostomes by the thinner walls between their zooecia. The specimens are erect forms, whereas these specimens are massive.

Order CYCLOSTOMATA

Cyclostomes are characterized by zooecia that are simple tubes which lack partitions (diaphragms) and have rounded apertures. and well defined mature and immature regions. Most cyclostomes are encrusting forms such as the example provided. , and some, like this small figured specimen encrusting a Devonian nautiloid cephalopod, can be quite small and very loosly arranged creeping zooecia.

Order FENESTRATA

Fenestrates are characterized by their zooaria morphology which form a mesh or net-like shape with zooecia-bearing rods and open window-like regions called fenstrules. Most fenestrates have considerable extra-zooid skeleton material which is necessary for support. This order is typified by erect, delicate morphology such as those seen in these specimens. Note, however, that some fenestrates have considerable extra-zooidal material such Archimedes which is an axial rod that supports the net-like zooecia.

Order CHEILOSTOMATA

Cheilostomes are characterized by their loosely packed colonies of box or coffin-shaped zooecium. Many have round apertures and large frontal areas on which brood pouches which house the maternal zooids can often be observed. .

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