''Eldonia'' is an extinct soft-bodied

cambroernid The Cambroernida are a clade of 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, meaning that their affinities wi ...

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 fos ...

, 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 The Canadian Rockies () or Canadian Rocky Mountains, comprising both the Alberta Rockies and the British Columbian Rockies, i ...

. In addition to over 550 specimens collected by Walcott, 224 specimens of ''Eldonia'' are known from the Greater Phyllopod bed, 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, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

strata of

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

Description

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 of hydrogen fluoride (HF) in water. Solutions of HF are colorless, acidic and highly corrosive. A common concentration is 49% (48–52%) but there are also stronger solutions (e.g. 70%) and pure HF has a boiling p ...

. A specimen from the Lower Ordovician Madaoyu Formation in

Hunan Hunan is an inland Provinces of China, province in Central China. Located in the middle reaches of the Yangtze watershed, it borders the Administrative divisions of China, province-level divisions of Hubei to the north, Jiangxi to the east, Gu ...

, South China, can be interpreted as the incomplete body of ''Eldonia'' or the similar animal. However, its annulation, the structure of the

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...

and the shape of the body are more similar to those of '' Ottoia''.

Classification

Walcott's original interpretation as a

holothurian Sea cucumbers are echinoderms from the class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number being in the Asia� ...

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

siphonophores Siphonophorae (from Ancient Greek σίφων (siphōn), meaning "tube" and -φόρος (-phóros), meaning "bearing") is an Order (biology), order within Hydrozoa, a class of marine organisms within the phylum Cnidaria. According to the World Re ...

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 (; ), also called Gorgo () or the Gorgon, was one of the three Gorgons. Medusa is generally described as a woman with living snakes in place of hair; her appearance was so hideous that anyone who looked upon her wa ...

. ''Eldonia'' and the other Eldoniidae form a clade,

Eldonioidea Eldonioids or velumbrellids are an extinct clade of disc-shaped cambroernids, the Eldonioidea (or Velumbrellida), which lived in the early to middle Paleozoic (Cambrian to Devonian). The terms "eldonioid" and "eldoniid" have been used somewhat in ...

, with the

Rotadiscidae Eldonioids or velumbrellids are an extinct clade of disc-shaped cambroernids, the Eldonioidea (or Velumbrellida), which lived in the early to middle Paleozoic (Cambrian to Devonian). The terms "eldonioid" and "eldoniid" have been used somewhat in ...

and the informal group known as the paropsonemids. The Eldonioidea are, in turn, part of the stem- ambulacrarian clade Cambroernida. There are three species within ''Eldonia'', although some authors consider ''E. eumorpha'' to be a distinct genus, '' Stellostomites'', as ''S. eumorphus''.

Paleoecology

The organism is frequently found in association with the lobopod '' Microdictyon'', which is presumed to have fed on ''Eldonia''. Eldonia berbera.jpg, ''Eldonia berbera'' Eldonia ludwigi, Burgess Shale.jpg, ''Eldonia ludwigii, '' Walcott Quarry. About 4 cm long

References

Works cited

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External links