The

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Microconchida is a group of small, spirally-coiled, encrusting fossil "worm" tubes from the class

Tentaculita Tentaculita is an extinct class of lophophorates ranging from the Early Ordovician to the Middle Jurassic. They were suspension feeders with a near worldwide distribution. For a more thorough discussion, see '' Tentaculites''. The presence of ...

found from the Upper

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

to the Middle

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

(

Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...

) around the world. They have lamellar calcitic shells, usually with pseudopunctae or punctae and a bulb-like origin. Many were long misidentified as the

polychaete Polychaeta () is a paraphyletic class of generally marine Annelid, annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called c ...

annelid ''

Spirorbis ''Spirorbis'' is a genus of very small () polychaete worms, usually with a white coiled shell. Members of the genus live in the littoral, lower littoral and Sublittoral zone, sublittoral zones of rocky shores. ''Spirorbis'' worms usually live att ...

'' until studies of shell microstructure and formation showed significant differences. All pre-Cretaceous "''Spirorbis''" fossils are now known to be microconchids. Their classification at the phylum level is still debated. Most likely they are some form of

lophophorate The Lophophorata (also called Tentaculata; not to be confused with Tentaculata Eschscholtz 1825, a class within the Ctenophora) are a Lophotrochozoan clade consisting of the Brachiozoa and the Bryozoa. They have a lophophore. Molecular phyloge ...

, a group which includes

phoronid Phoronids (Taxonomy (biology), taxonomic name Phoronida, sometimes called horseshoe worms) are a small phylum of marine animals that Filter feeder, filter-feed with a lophophore (a "crown" of tentacles), and build upright tubes of chitin to suppo ...

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

ns and

brachiopods Brachiopods (), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the fron ...

. Microconchids may be closely related to the other encrusting tentaculitoid tubeworms, such as ''

Anticalyptraea ''Anticalyptraea'' is a fossil genus (biology), genus of encrusting tentaculitoid tubeworms from the Silurian to Devonian of Europe and North America (Vinn, 2010). ''Anticalyptraea'' commonly encrust various invertebrate fossils such as Stromatop ...

'', trypanoporids and cornulitids. Their habitat is more controversial. While there is a consensus that they were present in the seas and in brackish water, there is a debate about their presence in freshwater. Some studies suggested that they colonised freshwater in the Early Devonian, whereas others suggest that microconchids never colonised that environment. A recent review of the associated fauna failed to find reliable occurrences of microconchids in the Middle

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

to Early

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

time interval because microconchids seem to co-occur with other signs of marine influence, such as xiphosurans and

chondrichthyan Chondrichthyes (; ) is a class (biology), class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which ...

egg capsules.

References

* Wilson, M.A., Yancey, T.E. and Vinn, O. 2011. "A new microconchid tubeworm from the Lower Permian (Artinskian) of central Texas, USA". ''

Acta Palaeontologica Polonica ''Acta Palaeontologica Polonica'' is a quarterly peer-reviewed open access scientific journal of paleontology and paleobiology. It was established by Roman Kozłowski in 1956. It is published by the Institute of Paleobiology of the Polish Academ ...

'' 56:785-791 . * Zaton, M., Wilson, M.A. and Vinn, O. 2012. "Redescription and neotype designation of the Middle Devonian microconchid (Tentaculita) species ''‘Spirorbis’ angulatus'' Hall, 1861". ''

Journal of Paleontology The ''Journal of Paleontology'' is a peer-reviewed scientific journal covering the field of paleontology. It is managed and published by Cambridge University Press on behalf of the Paleontological Society. Indexing The ''Journal of Paleontology ...

'' 86:417-424 . {{Taxonbar, from=Q6839384 Tentaculita Late Ordovician first appearances Middle Jurassic extinctions Prehistoric animal orders