The Edrioasteroids are an extinct class

Class (biology)

In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 of echinoderm

Echinoderm

Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....

 that lived from the Ediacaran

Ediacaran

The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...

 (if Arkarua

Arkarua

Arkarua is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of 5 small dots from the middle of the disk center...

was indeed an edrioaster) to the Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 periods of geologic time, about . The animals usually consisted of a disk-like upper body made of many plates.

The body plan for this class was simple: a main body (theca

Theca

A theca refers to any case, covering, or sheath.In botany, the theca of an angiosperm consists a pair of microsporangia that are adjacent to each other and share a common area of dehiscence called the stomium. Any part of a microsporophyll that bears microsporangia is called an anther. Most...

), composed of many small plates, a peripheral rim for attachment, and (in some species) a pedunculate zone for extension and retraction. Circling and sometimes attached to the body was a peripheral rim of plates. The main feature was the presence of five arms, or ambulacra

Ambulacral

Ambulacral is a term typically used in the context of anatomical parts of the phylum Echinodermata or class Asteroidea and Edrioasteroidea. Echinoderms can have ambulacral parts that include ossicles, plates, spines, and suckers. For example, sea stars or "star fish" have an ambulacral groove on...

, contained in the body wall radiating from the central mouth outwards. The ambulacra grew either curved or straight. When curved, they may all turn in the same direction or else one or two on the right side will curve opposite the others. The ambulacra are built of underlying floor plates that form the food groove and protective cover plates the roof the food groove. The anus

Anus

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...

 was situated under the mouth region and was made of small triangular plates to form a cone-shaped area. The bottom surface of the theca is unplated.

Edrioasteroid species are distinguished by differences in the ambulacral curvature, the relationships of the cover plates, and ornamentation. The mode of life was sessile; they were often attached via a stalk made of small plates to a hard object such as a carbonate hardground

Carbonate hardgrounds

Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor . A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone sequences and distinguished from later-lithified sediments by evidence of...

 or shell. Several examples of epibiotic attachment have also been noted.

In the discocystinids, the area between the body and peripheral rim could be extended and retracted; in so doing the two were separated. The peripheral rim became the base of the stalk which was attached to a surface. Underneath the body was a recumbent zone about 12 millimetre (0.47244094488189 in) wide in the genus Giganticlavus, followed by the pedunculate zone attached to the peripheral rim of 12 millimetre (0.47244094488189 in).

Taxonomy

• Mikko's taxonomy

List of genera

A very incomplete list of some genera.

• ?Arkarua
  Arkarua
  Arkarua is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of 5 small dots from the middle of the disk center...
  
  
  • ?A. adami (may be a Trilobozoan with pentamerous symmetry, and not an echinoderm at all)
• Walcotidiscus (oldest undisputed edruiasteroid, from the Middle Cambrian Burgess Shale
  Burgess Shale
  The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...
  
   community)
  • W. typicalus
• Kailidiscus
  Kailidiscus
  Kailidiscus is an extinct genus of echinoderm which existed in what is now China during the Middle Cambrian period. It was named by Yuanlong Zhao, Colin D. Sumrall, Ronald L. Parsley and Jin Peng in 2010, and the type and only species is Kailidiscus chinensis....
  
  
  • K. chinensis
• Edrioaster (type genus
  Type genus
  In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
  
  )
  • E. bigsbyi
  • E. priscus
• Edriophus
  • E. levis
• Paredriophus
  • P. elongatus
• Totiglobus
  • T. nimius
  • T. lloydi
• Lebedodiscus
• Foerstediscus
• Cystaster
• Cryptogoleus
• Bellochthus
• Cystaster
• Streptaster
  • S. vorticellatus
• Cystaster
  • C. stellatus
• Cryptogoleus
  • C. chapmani
• Carneyella
  • C. pilea
  • C. faberi
  • C. ulrichi
• Isorophus
  • I. cincinnatiensis
• Isorophusella
• Rectitriordo
• Agelacrinites
• Krama
  Krama
  A krama is a sturdy traditional Cambodian garment with many uses, including as a scarf, bandanna, to carry children, to cover the face, and for decorative purposes. It is worn by men, women and children, and can be fairly ornate, though most typical kramas contain a gingham pattern of some sort,...
  
  
• Parakrama
• Hemicystites
• Neoisorophusella
  • N. lanei
  • N. berryi
  • N. maslennikovi
  • N. whitesidei
• Curvitriordo
• Thresherodiscus
  • T. ramosa (Foerste, 1914)
• Postibulla
• Parapostibulla
• Eopostibulla
• Pyrgopostibulla
• Torquerisediscus
• Cooperidiscus
• Dynocystis
• Stalticodiscus
• Ulrichidiscus
• Clavidiscus
• Discocystis
• Hypsiclavus
• Spiraclavus
• Giganticlavus
• Lispidecodus
  • L. plinthotus (Kesling, 1967)

Taxonomy

• Mikko's taxonomy