''Microdictyon'' is an extinct armoured

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

-like animal coated with net-like scleritic plates, known from the Early

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

Maotianshan shale of Yunnan China and other parts of the world. ''Microdictyon'' is part of the ill-defined

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

–

Lobopodia The lobopodians, members of the informal group Lobopodia (from the Greek, meaning "blunt feet"), or the formally erected phylum Lobopoda Cavalier-Smith (1998), are panarthropods with stubby legs called lobopods, a term which may also be used as ...

– that includes several other odd worm-like

animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

s that resembling worm with legs, such as '' Hallucigenia'', '' Onychodictyon'', ''

Cardiodictyon ''Cardiodictyon'' is a genus of lobopodian known from 518 millions years old Chengjiang Lagerstätte. 525 millions years old partial fossil is also reported. It has ~25 pairs of legs, each associated with a pair of dorsal plates. Each leg termi ...

'', '' Luolishania'', and ''

Paucipodia ''Paucipodia inermis'' is a lobopod known from the Lower Cambrian Chengjiang lagerstätte. Its gut is puzzling; in some places, it is preserved in three dimensions, infilled with sediment; whereas in others it may be flat. These cannot result fr ...

''. The isolated sclerites of ''Microdictyon'' are known from other Lower

deposits. ''Microdictyon'' sclerites appear to have moulted; one sclerite seems to have been preserved during

ecdysis Ecdysis is the moulting of the cuticle in many invertebrates of the clade Ecdysozoa. Since the cuticle of these animals typically forms a largely inelastic exoskeleton, it is shed during growth and a new, larger covering is formed. The remnan ...

.Figured in ''Microdictyon sinicum'' (Chen, Hou and Lu, 1989) is typical. The wormlike animal has ten pairs of

sclerite A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...

s (suggestions that these may be eyes or eye-like structures have no weight) on the sides, matched to a pair of

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

-like feet below. The

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals ...

and posterior are tubular and featureless.

Species composition

Type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...

. ''Microdictyon effusum'' Bengtson, Matthews et Missarzhevsky, 1981; Lower Cambrian, Atdabanian Stage,

Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a transcontinental country located mainly in Central Asia and partly in Eastern Europe. It borders Russia to the north and west, China to the east, Kyrgyzstan to the southeast, Uzbeki ...

;

Atdabanian Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxim ...

and

Botomian Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission on ...

Stages,

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...

(

Siberian Platform Siberia, also known as Angaraland (or simply Angara) and Angarida, is an ancient craton in the heart of Siberia. Today forming the Central Siberian Plateau, it was an independent continent before the Permian period. The Verkhoyansk Sea, a passive ...

) and England; Lower Cambrian,

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic countries, Nordic c ...

. In addition to the type species, 13 species: *''M. anus'' Tong, 1989, Lower Cambrian, upper Meishucunian Stage (= Atdabanian Stage),

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

(

Shaanxi Shaanxi (alternatively Shensi, see § Name) is a landlocked province of China. Officially part of Northwest China, it borders the province-level divisions of Shanxi (NE, E), Henan (E), Hubei (SE), Chongqing (S), Sichuan (SW), Gansu (W), N ...

). *''M. chinense'' Hao et Shu, 1987, Lower Cambrian, Qiongzhusi Stage (= upper Atdabanian-lowermost Botomian Stages), China (Shaanxi); Atdabanian through Botomian stages, Siberian Platform. *''M. cuneum'' Wotte et Sundberg, 2017, Lower Cambrian, Montezuman Stage, the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

. *''M. depressum'' Bengtson, 1990, Lower Cambrian, Atdabanian through Botomian Stages, South

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

. *''M. fuchengense'' Li et Zhu, 2001, Lower Cambrian, upper Meishucunian Stage (Atdabanian Stage), China (Shaanxi). *''M. jinshaense'' Zhang et Aldridge, 2007, Lower Cambrian, Qiongzhusi Stage (= upper Atdabanian Stage-lowermost Botomian), China(Shaanxi). *''M. montezumaensis'' Wotte et Sundberg, 2017, Lower Cambrian, Montezuman Stage, the United States. *''M. rhomboidale'' Bengtson, Matthews et Missarzhevsky, 1986, Lower Cambrian, upper parts of the Atdabanian Stage, Kazakhstan; Atdabanian Stage,

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

, the United States (''M. cf. rhomboidale''). *''M. robisoni'' Bengtson, Matthews et Missarzhevsky, 1986, Middle Cambrian,

Amgan The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ( ...

Stage, the United States; *''M. rozanovi'' Demidenko, 2006, Lower Cambrian,

Toyonian Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission ...

Stage, Siberian Platform. *''M. sinicum'' Chen, Hou et Lu, 1989, Lower Cambrian, upper Meishucunian Stage (= Atdabanian Stage) Stage, China (

Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...

. *''M. sphaeroides'' Hinz, 1987, Lower Cambrian, Atdabanian Stage, Great Britain. *''M. tenuiporatum'' Bengtson, Matthews et Missarzhevsky, 1986, Lower Cambrian, Atdabanian Stage, Siberian Platform. A picture can be found at https://web.archive.org/web/20030730043530/http://paws.wcu.edu/dperlmutr/earlyfauna.html. ---- The name ''Microdictyon'' is also used for a genus of green

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

References

{{taxonbar, from1=Q20818056 Prehistoric protostome genera Maotianshan shales fossils Burgess Shale animals Paleozoic life of New Brunswick Paleozoic life of Nova Scotia Cambrian genus extinctions