[3] The animal superficially resembles another placozoan, Trichoplax adhaerens, but genetically distinct from it as mitochondrial DNA analysis revealed.

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.

[8] Schierwater, teaming up with Michael Eitel and Gert Wörheide from the 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] As do other placozoans, Hoilungia has only three anatomical parts as tissue layers inside its body: the upper, intermediate (middle) and lower epithelia.

[10] The middle layer is the thickest made up of numerous fiber cells, which contain mitochondrial complexes, vacuoles and endosymbiotic bacteria in the endoplasmic reticulum.

[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.

[3] 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.

[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.