The simplest animal on Earth might be a master of ancient, stable cloning

Nature · Published 3 October 2026 Swipe more like this →

In short: Trichoplax is a tiny, disc-shaped creature with no organs, no symmetry, and no nervous system. While scientists once thought it was a simple larva, it is actually a complex adult. New genomic research suggests these animals can thrive for decades in the wild without ever needing to reproduce sexually.

Discovered in 1883 by F.E. Schulze, the phylum Placozoa contains the simplest free-living multicellular animals known, featuring only six somatic cell types. These organisms are irregular, disc-shaped, and measure only a few millimeters across. Because of their minimal morphology and small genome—under 100 Mb—they have long been considered a potential surrogate for the last common ancestor of all animals, though this remains a subject of scientific debate.

The most widely distributed lineage, known as Trichoplax sp. H2, provides a unique window into animal evolution. Recent genomic analysis reveals that H2 and the reference lineage, Trichoplax adhaerens, share a highly similar genetic structure. Evidence suggests both lineages originated from a single interbreeding event at least several decades ago. Since that moment, they appear to have abandoned bisexual reproduction entirely, relying instead on vegetative, or clonal, division to maintain stable populations.

This reliance on cloning does not mean they are evolutionarily stagnant. Researchers suggest that rare sexual events, combined with the accumulation of somatic mutations, could allow these animals to rapidly generate genetic variation, creating new ecotypes. While laboratory cultures typically reproduce asexually, the ability to occasionally engage in sex may help them cope with environmental shifts or purge negative mutations. By studying the H2 genome, which shows a 99.1% identity to the reference, scientists are gaining a clearer picture of how such a simple design has persisted for so long.

The study of Trichoplax is complicated by its enigmatic life cycle and uniform appearance, which makes distinguishing species difficult. While some researchers have found molecular evidence for sex in specific Caribbean populations, the lack of observable anatomical variation across the phylum suggests that their simple bauplan is highly constrained. As a result, the H2 lineage is now considered a more suitable model system for understanding these mysterious, ancient animals than the original reference strain.

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