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

to the Middle Jurassic ( Bathonian) 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 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 so ...

'' 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, but on morphological grounds they have been assesse ...

, a group which includes

phoronid Phoronids (scientific name Phoronida, sometimes called horseshoe worms) are a small phylum of marine animals that filter-feed with a lophophore (a "crown" of tentacles), and build upright tubes of chitin to support and protect their soft bodies ...

s, bryozoans 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, ...

. Microconchids may be closely related to the other encrusting tentaculitoid tubeworms, such as '' Anticalyptraea'', 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 Carboniferous ( ) is a geologic period and syste ...

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'' 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 published by the Paleontological Society The Paleontological Society, formerly the Paleontological Society of America, is an interna ...

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