|Linnaean Hierarchy||Local Cladogram|
Archaeocyatha |--†Monocyathea |--0 †Archaeocyathea | |--†Ajacicyathida | |--†Metacyathida | |--0 †Acanthinocyathida | | `--0 †Acanthinocyathidae | | |--†Acanthinocyathus apertus | | `--†Pinacocyathus spicularis | |--0 †Hetairacyathida | | `--0 †Radiocyathidae | | `--0 †Radiocyathus minor | `--0 †Syringocnemida | `--0 †Syringocnematidae | |--†Syringocnema favus | |--†Syringocyathus aspectabilis | `--†Tubocyathus smolianinovae `--0 †Anthocyathea |--0 †Anthomorphida | `--0 †Anthomorphidae | `--0 †Anthomorpha margarita `--0 †Somphocyathida `--0 †Somphocyathidae `--0 †Somphocyathus coralloides
Archaeocyatha Incertae Sedis †Atikokania †Haguia †Matthewcyathus †Trachyum †Uranosphaera †Wilbernicyathus †Yakolevia
Stratigraphic Range: Early Cambrian
|Scientific history | Fossil record | Evolution | Phylogeny | Taxonomy | Characteristics | Ecology and Lifestyle | Links | References|
The Archaeocyatha, also called archaeocyathids, were sessile, reef-building marine organisms that lived during the Lower Cambrian period (500-600 million years ago). During the Lower Cambrian period, they were important reef-building organisms that formed gigantic mounds, called "bio-herms," from the accumulation of their skeletons. Around 520 million years ago, the archaeocyathids went into a steady decline, being displaced by sponges and algae as reef-builders. The final species became extinct prior to the start of the Ordovician, they are known only from fossils.
Archaeocyatha resemble hollow horn corals. Each had a conical or vase-shaped skeleton of calcite similar to that of a sponge. The structure is something like a pair of perforated, nested ice cream cones. Their skeletons consist of either a single porous wall (Monocyathida), or more commonly as two concentric porous walls, an inner and outer wall separated by a space. Inside the inner wall was a cavity (like the inside of an empty ice cream cone). At the base, they were held to substrate with a holdfast.
Archaeocyatha inhabited areas of shallow seas that were near the shoreline. Their widespread distribution over almost the entire world, as well as the diversity of the species, can be explained, among other things, by the fact that they, like many sponges, possessed a planktonic larval stage.
Though they have a long history of phylogenetic uncertainty and changing interpretations, consensus now has it that they were indeed a kind of sponge. Still, some authorities have placed them in the extinct phylum Archaeocyatha. Archaeocyatha were important reef builders in their time. Flow tank experiments suggest that their morphology allowed them to exploit flow gradients to passively pump water through the skeleton, as in modern sponges.