Fossil Bryozoan Archimedes regina mm 18 x 7 only a piece as in picture.
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Archimedes is a genus of fenestrated bryozoans with calcified skeleton, belonging to the Fenestellidae family.
It was called Archimedes in 1838 because of its corkscrew shape, in analogy with the screw of Archimede, a type of water pump that inspired the modern naval propellers. These forms are quite common as fossils but are extinct by the Permian.
These bryozoans lived from the Carboniferous period to the Permian period (345 to 268 million years ago), when this kind became extinct.
The most common remains are fragments of the limestone mesh detached from the central structure. Samples in which the network remains attached to the central structure are rare. Like other bryozoans, Archimedes formed colonies; within the branches, the neighboring individuals were in contact through small channels. Most of these fossils are distributed in Europe and North America, but have also been found in sediments in Afghanistan, Canada, Russia and Australia.
The phylum
Bryozoa (Briozoi) or, more correctly, Ectoprocta, is composed of small aquatic invertebrates, almost exclusively marine, living in arborescent colonies anchored to a submerged substrate. They are also called encrusting organisms because they cause fouling on the hulls of ships and on submerged marine structures.
The name derives from the Greek bryon = moss and zoion = animal, since the appearance of the colonies resembles that of the moss.
The Bryozoans live on rocky bottoms, but also sandy and silty, prefer tropical marine environments, however for their worldwide distribution they can be called cosmopolitan.
A colony of bryozoans is made up of individuals reaching a maximum of half a millimeter. Everyone lives enclosed in an elongated double-walled shell, calcareous or chitinous, sometimes closed by an operculum.
Each individual is made up of a part that is permanently inside the case, and one that emerges, in the shape of an octopus, with a raised ridge, the lophophorus (they are also called Lophophorates, like the brachiopods), which bears a crown of tentacles around the buccal opening, which act as organs for feeding, breathing and perception of external stimuli.
The lophophorus in the marine bryozoons has a circular shape, while in those of fresh water it is shaped like a horseshoe. They feed on plankton and organic particles that they capture by filtering the water.
They have a U-shaped digestive tract, with the mouth near the anus at the top and stomach and intestine in the lower one.
Colonies are generally polymorphic, ie they can take on a different shape depending on their function (cleaning, reproduction, defense, etc.).
Bryozoans are generally sexually hermaphrodites. From the embryo develops a ciliated larva type trocofora, shaped like a flattened cone with an apical tuft of eyelashes. The larvae, after hatching, descend on the sea bed and, with the apex facing downwards, attach themselves to a substrate, founding a new colony for budding.
The Bryozoa also include the Entoprocta subtype, with mouth and anus opening inside the lophophorus. There is no fossil record of these forms, for they are skeleton-free.
From studies on fossil findings it emerges that the Bryozoans have appeared, with countless species, in the Cambrian, and had the greatest expansion in the period between the Ordovician and the Carboniferous, with the appearance of numerous new species, and in the period between Jurassic and Cretaceous.
Currently about 4000 species are known, most of which dates back to the Paleozoic, and more than 15,000 fossil species.
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