Everything about Archaeocyatha totally explained
The
Archaeocyatha or
archaeocyathids ("ancient cups") were
sessile,
reef-building
marine organisms of warm tropical and subtropical waters that lived during the early (lower)
Cambrian period. They are first known from the beginning of the
Tommotian Age of the Cambrian, about 530 million years ago (
mya), and quickly
diversified into over a hundred
families. They became the planet's very first
reef building animals.
Today, the
archaeocyathan families are recognizable by small but consistent differences in their
fossilized structures: Some
archaeocyathans were built like nested bowls, while others were as long as 30 cm. Some
archaeocyaths were solitary organisms, while others formed
colonies. Then, around 520
mya, the archaeocyaths went into a sharp decline. Almost all species became
extinct by the Middle Cambrian, with the final-known species disappearing just prior to the end of the Cambrian period. Their rapid decline and disappearance coincided with a rapid
diversification of the
Demosponges.
The typical
archaeocyathd resembled a hollow
horn coral. Each had a conical or vase-shaped porous
skeleton of
calcite similar to that of a
sponge. The structure appeared like a pair of perforated, nested ice cream cones. Their skeletons consisted 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, these
pleosponges were held to
substrate with
holdfast. The body presumably occupied the space between the inner and outer shells (the
intervallum). Flow tank experiments suggest that
archaeocyathan morphology allowed them to exploit flow gradients, either by passively pumping water through the
skeleton, or, as in present-day,
extant sponges, by drawing water through the
pores, removing nutrients, and expelling spent water and wastes through the pores into the central space.
The archaeocyathans inhabited coastal areas of shallow seas. Their widespread distribution over almost the entire Cambrian world, as well as the
taxonomic diversity of the
species, might be explained by surmising that that they were
planktonic during their
larval stage.
Their
phylogenetic affiliation has been subject to changing interpretations: Yet the consensus is growing that the
archaeocyath was indeed a kind of sponge,thus sometimes called a pleosponge. But some
invertebrate paleontologists have placed them in an extinct, separate
phylum, known appropriately as the Archaeocyatha. However, one
cladistic analysis suggests that Archaeocyatha is a
clade nested within the
phylum Porifera (better known as the true sponges).
Further Information
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