These microscopic animals live their entire lives in a world without any oxygen

Nature · Published 3 October 2026 Swipe more like this →

In short: Loricifera are tiny, armored creatures that remained hidden from science until 1983 because they cling tightly to marine gravel. While most animals require oxygen to survive, some loriciferans thrive in the deep, anoxic basins of the Mediterranean Sea, challenging our fundamental understanding of what it means to be multicellular.

Loricifera, or corset animals, are a phylum of microscopic organisms ranging from 100 micrometers to about one millimeter in length. They possess a complex anatomy, including a brain, a mouth, and a protective outer shell known as a lorica. Despite their sophistication, they lack circulatory or endocrine systems. Their evolutionary history is difficult to trace due to a scarce fossil record, though some fossils have been dated to the late Cambrian period. Researchers believe these creatures may be miniaturized descendants of larger, ancient organisms.

The phylum was first described by R.M. Kristensen in 1983, following collections made in the 1970s near Roscoff, France. Their classification remains a subject of intense scientific debate. Traditionally grouped with Priapulida and Kinorhyncha in the taxon Scalidophora, recent genetic studies have offered conflicting results. Some research suggests they may be more closely related to Nematoda or Panarthropoda, while other findings continue to support the monophyly of Scalidophora, leaving the true evolutionary position of these animals unsettled.

Perhaps the most striking discovery regarding Loricifera is their ability to inhabit extreme environments. In the L'Atalante basin of the Mediterranean Sea, more than 3,000 meters deep, three species were found living in a hypersaline, anoxic environment. This brine is completely devoid of oxygen and contains high concentrations of sulphide. Initially, scientists hypothesized that these animals respired anaerobically using mitochondria that functioned like hydrogenosomes. However, by 2021, the presence of mitochondria in these specific organisms became a point of scientific questioning, leaving the mechanism of their survival in such harsh conditions a compelling mystery.

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