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This short-lived but widespread group have been classed by various as sponges, corals, or calcareous algae. Archaeocyaths now are almost unversally considered as subphylum of the Porifera (possibly related to the demosponges); a few workers still group them in a separate phylum (Phylum Archaeocyatha). They range mainly from basal Cambrian to late Early Cambrian (a few forms persisted to Middle and Late Cambrian).

One of the earliest groups to secrete substantial skeletal calcium carbonate and the first reef-building organism.

Sessile, benthic, filter feeders. Exclusively marine organisms that lived in tropical, normal salinity (ca. 30-40 ppt) waters at depths from the intertidal zone to a few tens of meters, mainly in areas with relatively low influx of terrigenous sediments (see Debrenne and Reitner, 2001).

Constructed small bioherms in association with calcimicrobes. They also are found in lesser abundance, size and diversity in inter-bioherm areas.

The good preservation of most archaeocyath skeletal material indicates a primary calcitic composition.

Most archaeocyaths have a solitary cup- or bowl-shaped skeleton that has a pair of porous walls enclosing a large central cavity. The inner and outer walls have a series of spherical perforations and are connected by numerous perforate or imperforate partitions (vertical septa and horizontal tabulae).

Less commonly, archaeocyaths had branched, massive, or chain-like colonial forms.

The average size of archaeocyath cups is 1 to 2.5 cm in diameter and 15 cm in height. Cups as small as 2-3 mm or as large as 60 cm in diameter are known, however.

Closely associated with calcimicrobial encrusters such as Renalcis and/or Epiphyton, and external morphology is commonly outlined by such encrusters.

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