The

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

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

Tentaculita Tentaculita is an extinct class of uncertain placement 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 presen ...

found from the Upper

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

to the Middle

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

(

Bathonian In the geologic timescale the Bathonian is an age and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian Age succeeds the Bajocian Age and precedes the Callovian Age. ...

) 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 worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made ...

annelid ''

Spirorbis ''Spirorbis'' is a genus of very small () polychaete worms, usually with a white coiled shell. Members of the genus live in the lower littoral and sublittoral zones of rocky shores. ''Spirorbis'' worms usually live attached to seaweeds, but som ...

'' 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 are a Lophotrochozoan clade consisting of the Brachiozoa and the Bryozoa. They have a lophophore. Molecular phylogenetic analyses suggest that lophophorates are protostomes Protostomia () is the clade of animals once though ...

, a group which includes phoronids,

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

ns and

brachiopods Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan 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, wh ...

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

Anticalyptraea ''Anticalyptraea'' is a fossil 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 stromatoporoids, rugose ...

'', trypanoporids and

cornulitids Cornulitida is an extinct order of encrusting animals from class Tentaculita, which were common around the globe in the Ordovician to Devonian oceans, and survived until the Carboniferous. The organisms had shells, and were subject to predation ...

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 Academy ...

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