''Eldonia'' is an extinct soft-bodied

cambroernid The cambroernids are an informally-named clade of unusual Paleozoic animals with coiled bodies and filamentous tentacles. They include a number of early to middle Paleozoic ( Cambrian to Devonian) genera noted as 'bizarre" or "orphan" taxa, mean ...

animal of unknown affinity, best known from the Fossil Ridge outcrops of the

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest foss ...

, particularly in the 'Great ''Eldonia'' layer' in the

Walcott Quarry The Walcott Quarry is the most famous quarry of the Middle Cambrian Burgess Shale, located in the Canadian Rockies of British Columbia, bearing the Phyllopod beds. This lies at the base of the Walcott Quarry member, on a ridge between Wapta Mou ...

. In addition to the 550 collected by Walcott, 224 specimens of ''Eldonia'' are known from the Greater

Phyllopod bed The Phyllopod bed, designated by USNM locality number 35k, is the most famous fossil-bearing member of the Burgess Shale fossil ''Lagerstätte''. It was quarried by Charles Walcott from 1911–1917 (and later named Walcott Quarry), and was t ...

, where they comprise 0.43% of the community. Species also occur in the Chengjiang biota, Siberia, and in Upper

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

strata of

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to ...

. Walcott's original interpretation as a

holothurian Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothurian ...

was rapidly disputed. Alternative affinities to be suggested, which did not stand the test of time, included the

siphonophores Siphonophorae (from Greek ''siphōn'' 'tube' + ''pherein'' 'to bear') is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 specie ...

and a

coelenterate Radiata or Radiates is a historical taxonomic rank that was used to classify animals with radially symmetric body plans. The term Radiata is no longer accepted, as it united several different groupings of animals that do not form a monophyletic ...

medusa In Greek mythology, Medusa (; Ancient Greek: Μέδουσα "guardian, protectress"), also called Gorgo, was one of the three monstrous Gorgons, generally described as winged human females with living venomous snakes in place of hair. Those ...

. It takes the form of a round, medusoid disk (which originally led to suggestions of a jellyfish affinity) with a C-shaped gut trace. The gut is recalcitrant and can be extracted using

Hydrofluoric acid Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...

. The organism is frequently found in association with the lobopod ''

Microdictyon ''Microdictyon'' is an extinct armoured worm-like animal coated with net-like scleritic plates, known from the Early Cambrian Maotianshan shale of Yunnan China and other parts of the world. ''Microdictyon'' is part of the ill-defined taxon &ndash ...

'', which is presumed to have fed on ''Eldonia''. The eldoniids form a clade that also includes ''

Paropsonema ''Paropsonema'' is a discoidal animal known from the Cambrian Chengjiang biota The Maotianshan Shales are a series of Early Cambrian deposits in the Chiungchussu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the ...

'', ''

Rotadiscus ''Rotadiscus'' is a genus of discoidal animal known from the Cambrian Chengjiang biota The Maotianshan Shales are a series of Early Cambrian deposits in the Chiungchussu Formation, famous for their '' Konservat Lagerstätten'', deposits known ...

'', and ''

Stellostomites ''Stellostomites'' is a discoidal animal known from the Cambrian Chengjiang biota The Maotianshan Shales are a series of Early Cambrian deposits in the Chiungchussu Formation, famous for their '' Konservat Lagerstätten'', deposits known for th ...

''. Eldonia berbera.jpg, ''Eldonia berbera'' Eldonia ludwigi, Burgess Shale.jpg, ''Eldonia ludwigii, '' Walcott Quarry. About 4 cm long

References

External links

* {{Taxonbar, from=Q1421766 Prehistoric animal genera Burgess Shale fossils Middle Ordovician genus extinctions Wheeler Shale Cambrian genus extinctions Ordovician genus extinctions