Hoilungia

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Hoilungia
Microscopic image of Hoilungia hongkongensis. Scale bar is 0.2 mm.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Placozoa
Class: Uniplacotomia
Order: Hoilungea
Family: Hoilungidae
Genus: Hoilungia
Eitel, Schierwater & Wörheide, 2018
Species:
H. hongkongensis
Binomial name
Hoilungia hongkongensis
Eitel, Schierwater & Wörheide, 2018

Hoilungia is a genus that contains one of the simplest animals and belongs to the

Trichoplax adhaerens, but genetically distinct from it as mitochondrial DNA analysis revealed.[1]

Hoilungia was discovered in brackish water from mangrove swamps in Hong Kong.

cnidarians. They are diploblastic animals and are believed to have dorso-ventral polarity along top and bottom body layers. Their body is overtly similar to oral-aboral axis of cnidarians.[5]

Discovery

Trichoplax adhaerens was discovered by the German zoologist Franz Eilhard Schulze in 1883. But its identification as to what kind of animal it was (systematic position) was not known.[6] Another German, Karl Gottlieb Grell, discovered the diversity of these animals and created a new phylum Placozoa, in 1971. Grell derived the name from the placula hypothesis, Otto Bütschli's notion on the origin of metazoans.[7]

The advent of molecular techniques allowed genetic analysis of placozoans. The first important report in 2004 by a team of zoologists at the Institute of Animal Ecology & Cell Biology in Hannover, Germany, led by Allen G. Collins and Bernd Schierwater, indicated that placozoans known under T. adhaerens could be genetically many species.

Ludwig-Maximilians-Universität München, made further studies and found that the specimen H13 was a different placozoan animal for which they introduced the genus Hoilungia, and the species H. hongkongensis, in 2018.[1][3]

Etymology

The genus name is derived from the phrase "hoi lung", which means "sea dragon" in Cantonese. The species name is after Hong Kong from where it was discovered.[1]

Biology

Structure

Ultrastructure of Hoilungia Hongkongensis. The upper epithelium (blue bar) with monociliated cells (light blue). The intermediate layer (green bar) consists of nonciliated fiber cells (labeled “fc” in light green). The lower epithelium (orange bar) is mostly made up of monociliated cylinder cells (light red). Scale bar is 2 μm.

Hoilungia do not have well-defined body plan much like

amoebas, unicellular eukaryotes. As Andrew Masterson reported, "[as other placozoans] they are as close as it is possible to get to being simply a little living blob."[9] An individual body measures about 0.55 mm in diameter.[3] There are no body parts; as Eitel described: "There's no mouth, there's no back, no nerve cells, nothing."[1]

As do other placozoans, Hoilungia has only three anatomical parts as tissue layers inside its body: the upper, intermediate (middle) and lower

secretory granule.[3]

The body axes of Hoilungia and Trichoplax are overtly similar to the oral–aboral axis of

cnidarians,[5] animals from another phylum with which they are most closely related.[11] Structurally, they can not be distinguished from other placozoans, so that identification is purely on genetic (mitochondrial DNA) differences.[3] Genome sequencing has shown that Hoilungia have 164 unique genes and 9 uniquely missing genes compared to other placozoans.[12]

Nutrition

Hoilungia feed on algae, bacteria, yeast and other byproducts of biofilms. They feed from lower tissue layer which has various peptidergic gland cells.[3]

Reproduction

Hoilungia reproduce asexually through

binary fission and budding. It is also possible that they also reproduce sexually.[3]

Evolutionary history

Hoilungia and Trichoplax are considered one of the earliest branching animal lineages, and have relatively simple morphologies their complexity of NO-cGMP-mediated signaling is greater to those in vertebrates. This evidence has been found in their DNA by experimentation using ultra-sensitive capillary electrophoresis assays.[3] The genomes of H. hongkongensis and other placozoans add support to the phylogenetic placement of the Placozoa as the most ancient (basal) animals in the tree of life.[12]

References

  1. ^ a b c d e Wood, Charlie (2018-10-06). "Simplest Animal Reveals Hidden Diversity". Scientific American. Retrieved 2023-06-02 – via Quanta Magazine.
  2. ^ World Placozoa Database. "Hoilungia hongkongensis Eitel, Schierwater & Wörheide, 2018". World Register of Marine Species. Retrieved 18 August 2020.
  3. ^
    PMID 30063702
    .
  4. ^ Wood C (6 October 2018). "World's simplest animal reveals hidden diversity". Quanta Magazine.
  5. ^
    PMID 30726986
    .
  6. S2CID 237387715
    .
  7. S2CID 235331464
    .
  8. S2CID 11539852
    .
  9. ^ Masterson, Andrew (2018-08-01). "Simple organisms not so simple, after all". Cosmos Magazine. Retrieved 2023-06-02.
  10. ^
    PMID 33876313
    .
  11. PMID 31288696
    .
  12. ^
    ISSN 2296-701X
    .
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