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An extinct phylum of reef-forming organisms known only from the Cambrian. They were cup-like, usually 10–30 mm in diameter and up to 50 mm high. The cylindrical, conical, or discoid cup often had an irregular outline or outgrowths. The outer wall had simple pores or was partially displaced by dissepiments. The inner wall usually had one longitudinal row of pores between intercepts. The intervallum contains dissepiments, rods, and bars or septa. Some were solitary, others colonial. In some respects they were similar to both sponges and corals, and may represent a true advance in evolutionary grade over the former. It is possible that they lived in a symbiotic relationship with some trilobites. The cause of their extinction is not known.

Subjects: Zoology and Animal Sciences — Earth Sciences and Geography.

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