Microdictyon

Microdictyon is an extinct "armored worm" coated with dot-like scleritic scales, known from the Early Cambrian Maotianshan shale of Yunnan China. Microdictyon is sometimes included in a somewhat ill-defined Phylum – Lobopodia – that includes several other odd worm-like and segmented free-swimming animals that do not appear to be arthropods or worms. The phylum includes Microdictyon, Onychodictyon, Cardiodictyon, Luolishania, Paucipodia, as well as the Anomalocarids. The isolated sclerites of Microdictyon are known from other Lower Cambrian deposits. (The famous Hallucigenia from the Cambrian-age Burgess Shales was once considered to belong to the family Lobopodia, but is now recognized as an Onychophoran, a relative of the velvet worms.)

Microdictyon sinicum (Chen, Hou and Lu, 1989) is typical. The wormlike animal has ten pairs of sclerites on the sides, matched to a pair of tentacle-like feet below. The head and posterior are tubular and featureless.

Species composition

• Type species. Microdictyon effusum Bengtson, Matthews et Missarzhevsky, 1981; Lower Cambrian, Atdabanian Stage, Kazakhstan; Atdabanian and Botomian Stages, Russia (Siberian Platform) and England; Lower Cambrian, Sweden.

In addition to the type species, eleven species:^[1]

• M. anus Tong, 1989, Lower Cambrian, upper Meishucunian Stage (= Atdabanian Stage), China (Shaanxi).
• M. chinense Hao et Shu, 1987, Lower Cambrian, Qiongzhusi Stage (= upper Atdabanian-lowermost Botomian Stages), China (Shaanxi); Atdabanian through Botomian stages, Siberian Platform.
• M. depressum Bengtson, 1990, Lower Cambrian, Atdabanian through Botomian Stages, South Australia.
• 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).^[2]
• M. rhomboidale Bengtson, Matthews et Missarzhevsky, 1986, Lower Cambrian, upper parts of the Atdabanian Stage, Kazakhstan; Atdabanian Stage, Canada, the United States (M. cf. rhomboidale).
• M. robisoni Bengtson, Matthews et Missarzhevsky, 1986, Middle Cambrian, Amgan Stage, the United States;
• M. rozanovi Demidenko, 2006, Lower Cambrian, Toyonian Stage, Siberian Platform.^[1]
• M. sinicum Chen, Hou et Lu, 1989, Lower Cambrian, upper Meishucunian Stage (= Atdabanian Stage) Stage, China (Yunnan.
• 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 http://paws.wcu.edu/dperlmutr/earlyfauna.html.

The name Microdictyon is also used for a genus of green algae.

References