Hallucigenia

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Hallucigenia
Temporal range: Cambrian Stage 3–Middle Cambrian
Fossil holotype of Hallucigenia sparsa from the Burgess Shale
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
(unranked): Panarthropoda
Phylum: "Lobopodia"
Clade:
Hallucishaniids
Family: Hallucigeniidae
Genus: Hallucigenia
Conway Morris, 1977[1]
Species
  • H. sparsa (Walcott, 1911) (type)
  • H. fortis Hou & Bergström, 1995[2]
  • H. hongmeia Steiner et al 2012[3]
Synonyms

Canadia
sparsa

Hallucigenia is a genus of

water bears, and arthropods arose.[5][4]

Description

Reconstructions of H. fortis, H. hongmeia, and H. sparsa in scale.

Hallucigenia is a 0.5–5.5 cm (3162+316 in)

lobopods). The first 2 or 3 leg pairs are slender and featureless,[6][7][8] while the remaining 7 or 8 pairs each terminate with 1 or 2 claws.[9][7][8] Above the trunk region are 7 pairs of rigid conical sclerites (spines) corresponding to the 3rd–9th leg pairs.[9][6][7][8] The trunk is either featureless (H. sparsa)[7] or divided by heteronomous annulations (H. fortis[2] and H. hongmeia).[9][10] The "head" and "tail" end of the animal are difficult to identify; one end extends some distance beyond the legs and often droops down as if to reach the substrate. Some specimens display traces of a simple gut.[7]

Research in the mid-2010s clarified that the longer end is a head with anteroventral mouth and at least a pair of

simple eyes.[11][6][7] The shape of head differs between species – elongated in H. sparsa, rounded in H. fortis,[6][7] while those of H. hongmeia remain unknown.[9] At least in H. sparsa, the head possesses radial teeth and pharyngeal teeth within the front of the gut.[7][12]

Hallucigenia's spines are made up of one to four nested elements. The spine surface of H. sparsa is covered in an ornament of minute triangular 'scales',[13] while the spine surface of Hallucigenia hongmeia is a net-like texture of microscopic circular openings, which can be interpreted as the remains of Papillae.[9]

History of study

Various interpretations of Hallucigenia sparsa throughout the history of study

Hallucigenia sparsa was originally described by

Canadia.[14] In his 1977 redescription of the organism, Simon Conway Morris recognized the animal as something quite distinct, for which he proposed the name Hallucigenia because of the "bizarre and dream-like appearance of the animal." No specimen was available that showed both rows of legs, so Conway Morris reconstructed the animal walking on its spines, with its single row of legs interpreted as tentacles on the animal's back. A dark stain at one end of the animal was interpreted as a featureless head. Only the forward tentacles could easily reach to the 'head', meaning that a mouth on the head would have to be fed by passing food along the line of tentacles. Conway Morris suggested that a hollow tube within each of the tentacles might be a mouth.[1] This raised questions, such as how it would walk on the stiff legs, but it was accepted (with reservations) as the best available interpretation.[15]

Specimen with obvious spines

An alternative interpretation considered Hallucigenia to be an appendage of a larger, unknown animal. There had been precedent for this, as Anomalocaris had been originally identified as three separate creatures before being identified as a single huge (for its time) 1-metre-long (3 ft) creature.[15]

In 1991, Lars Ramskold and

onychophoran (velvet worm) at that time.[16][5] They inverted it, interpreting the tentacles, which they believe to be paired, as walking structures and the spines as protective.[16] Further preparation of fossil specimens showed that the 'second legs' were buried at an angle to the plane along which the rock had split, and could be revealed by removing the overlying sediment.[17] Ramskold and Hou also believe that the blob-like 'head' is actually a stain that appears in many specimens, not a preserved portion of the anatomy.[16] This stain may be an artifact of decomposition.[7]

Affinity

Restoration of H. sparsa
External videos
video icon Hallucigenia: The worm with the missing head Nature Video, YouTube.

Since the revisions around 1990s,

ecdysozoan, but lost in the modern onychophorans – in particular its distinctive foregut armature.[7]

Below is a cladogram for Hallucigenia according to Yang et al., 2015:[18]

Microdictyon

Cardiodictyon

Hallucigenia sparsa

Hallucigenia fortis

Hallucigenia hongmeia

Luolishaniidae

Acinocricus

Collinsovermis

Luolishania

Collinsium

Diversity

In 2002,

Desmond Collins informally suggested that new Hallucigenia fossils from the Burgess Shale showed male and female forms, one with "a rigid trunk, robust neck and a globular head" and the other thinner, and with a small head.[22]

Three species of Hallucigenia have been described. The first specimen, Hallucigenia sparsa, was discovered in Canada. Two other species, H. fortis and H. hongmeia, are represented by the Maotianshan Shales' fossils of Chengjiang.[2][3]

Distribution

Hallucigenia was first described from the Burgess Shale in southeastern

mineralized fossils.[13]

In popular culture

Hallucigenia is featured in the Japanese anime Attack on Titan. Believed to be the origin of all living matter and pivotal to Ymir Fritz's transformation, the Hallucigenia begins the violent conflicts that make up the main storyline of the franchise. After Eren Yaeger is decapitated by Gabi Braun, the anomaly manifests from Eren's body and reattaches itself to his head.[24]

See also

References

  1. ^ a b c Conway Morris, S. (1977). "A new metazoan from the Cambrian Burgess Shale of British Columbia" (PDF). Palaeontology. 20: 623–640. Archived from the original (PDF) on 31 March 2017. Retrieved 27 January 2021.
  2. ^
    ISSN 0024-4082
    .
  3. ^ .
  4. ^ a b Zimmer, Carl (2 July 2015). "The Cambrian Explosion's Strange-Looking Poster Child". The New York Times. Retrieved 2 July 2015.
  5. ^
    PMID 26439350
    .
  6. ^ .
  7. ^ .
  8. ^ .
  9. ^ .
  10. ^ .
  11. .
  12. ^ Morelle, Rebecca, Face of bizarre sea creature Hallucigenia revealed, BBCNews, Science and Environment, 2015.06.25
  13. ^
    PMID 23902914
    .
  14. ^ WALCOTT, C. 1911. Cambrian Geology and Paleontology II. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(5): 109–145.
  15. ^ .
  16. ^ .
  17. ^ .
  18. ^ .
  19. .
  20. .
  21. ^ .
  22. ^ Collins, Desmond (2002). "Hallucigenia unveiled. Abstracts, Palaeontological Association, 46th annual meeting" (PDF). Palaeontology Newsletter. 51: 85–6. Archived from the original (PDF) on 3 March 2016.
  23. S2CID 53646959
    .
  24. ^ Gonzalez, Sebastian Adolfo Osio (18 November 2023). "Attack on Titan Finale: What is the Hallucigenia Worm?". DualShockers. Retrieved 26 February 2024.

Further reading

External links