Cheungkongella Ancestralis

''Cheungkongella'' is a fossil organism from the lower Cambrian Chengjiang lagerstatte, the affinity of which has been the subject of debate. It was announced as a "probable" tunicate while noting the lack of definitive Cambrian fossils from that group. However, this affinity was later disputed in a paper announcing the discovery of ''Shankouclava'', also from Chengjiang, as the oldest known tunicate. ''Cheungkongella'' has been accepted as a distinct taxon and possible tunicate by multiple workers not involved in its discovery, but the dispute remains unresolved.

Etymology

"Cheungkong" is "a metaphor of China" and honors the Cheungkong Scholars Programme's support for the work leading to the fossil's discovery. "Ancestralis" refers to the fossil's possible primitive taxonomic position.

Description

''Cheungkongella'' has a club-shaped body similar to the extant ascidian '' Styela'', with a bucket-shaped main body with thick, tapering stem beneath it. A large oral siphon with short tentacles at the top of the animal leads to a pharynx occupying two-thirds of the main body, with a structure presumed to ben an alimentary canal beneath it. A small cloacal siphon emerges from the side above the transition to the stem.

Classification

''Cheungkongella'' was placed in the class Ascidiacea based on its resemblance ''Styela''. This classification was initially accepted by other workers.

Proposal to synonomize with ''Phlogites''

A 2003 paper announcing ''Shankouclava'' as the oldest known tunicate both disputed ''Cheungkongellas affinities and proposed that it is a junior synonym of ''Phlogites'', which was though to be a lophophorate at the time

The paper stated that ''Cheungkongella'' is "indistinguishable" from ''Phlogites'', but proceeded to note several differences, most notably the lack of any "obvious" arms in ''Cheungkongella'' despite acknowledging that three or five such arms are a prominent feature of ''Phlogites''. The paper speculated that this is "perhaps because its arms broke off or are covered by rock." The lack of a coiled gut in ''Cheunkongella'' was dismissed by noting that not all specimens of ''Phlogites'' display one.

The original description of ''Cheungkongella'' noted light dots in the area interpreted as a pharynx that could be gill slits, but stated that the interpretation required confirmation. The ''Shankouclava'' paper suggested that these dots are taphonomic artifacts due to their irregular pattern. However, the paper's other arguments against tunicate affinities were based on newly discovered specimens of ''Phlogites''. ''Phlogites'' is now known to be a cambroernid, and has never been assigned to the tunicates except as a result of ''Cheungkongella'' being considered a synonym.

A responding paper disputing the synonymization with ''Phlogites'' provided the image shown on this page in response to criticisms of poor image quality in past publications.

A paper on the affinities of ''Phlogites'' accepted the synonymization, but did not discuss the ''Cheungkongella'' fossil except to note a similar thickness of stem between it and a subset of the new ''Phlogites'' specimens. The similarity of the lower section has also been noted by workers who consider the two taxa to be separate.

The resemblance between ''Cheunkongella'' and ''Phlogites'' has been dismissed as "superficial" by a researcher not involved with the discoveries of either of those taxa or of ''Shankcouklava''. Other sources not directly involved in the dispute have recognized both ''Cheungkongella'' (as distinct from ''Phlogites'') and ''Shankouclava'' as possible (if debatable) tunicates, or recognize ''Cheungkongella'' as a tunicate and ''Shankouclava'' as chordate.

The dispute remains unresolved, as has been noted by sources that accept or tentatively accept the synonymization.

References

Works cited

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{{Taxonbar, from=Q5094270

Tunicate genera
Prehistoric chordate genera
Fossil taxa described in 2001
Cambrian genus extinctions
Ascidiacea