Evolutionary Trends of Zooidal Shape

Extract

The individual functioning units (zooids) in stenolaemate bryozoan colonies include skeletal portions called zooecia (singular, zooecium). Within a zooecium there may be basal diaphragms that make the occupied portion (living chamber) shorter than the full length of the zooecium, and there may be various skeletal parts that project into and modify the shape of the living chamber. The entire zooecium constitutes a record of zooidal ontogeny and of the geometrical relationships between neighboring zooecia or between zooecia and the surrounding colonial tissues. Therefore, evolutionary changes in zooecial shape reflect changes in all stages of zooidal ontogeny and in relationships between zooids and their surrounding intracolonial environment. In addition, evolutionary changes in zooidal size have affected zooecial shape in some stenolaemate groups.