Breathless Animals

The term animal comes from the Latin animalis, meaning “having breath.” But not all animals breathe.

A few nematodes living deep underground are known to sip scant oxygen. The common breadcrumb sponge, native to the North Atlantic Ocean and Mediterrean Sea, is also not a heavy breather.

A certain cnidarian parasite that prefers salmon has been found to have dispensed with breathing altogether. Israeli zoologist Dayana Yahalomi explains: “Mitochondrial respiration is an ancient characteristic of eukaryotes. However, it was lost independently in multiple eukaryotic lineages as part of adaptations to an anaerobic lifestyle. A similar adaptation occurred in a member of the Myxozoa, a large group of microscopic parasitic animals that are closely related to jellyfish and hydroids.”

Mitochondria are the organelle power plant for cells. In animals, mitochondria are oxygen suckers that use the gas to fabricate power for cellular energy.

Yahalomi continues: “The acquisition of the mitochondrion was a fundamental event in the evolution of eukaryotes, and most extant eukaryotes cannot survive without oxygen. The loss of aerobic respiration has occurred independently in several eukaryotic lineages that adapted to low-oxygen environments and replaced the standard mitochondrial oxidative phosphorylation pathway with novel anaerobic metabolic mechanisms.”

Henneguya salminicola is distantly related to jellyfish. For part of its life, H. salminicola lives in marine worms which salmon eat, thereby giving the parasite entry into its favored host.

“It is generally thought that during evolution, organisms become more and more complex, and that simple single-celled or few-celled organisms are the ancestors of complex organisms. But here is an animal whose evolutionary process is the opposite. Living in an oxygen-free environment, it has shed unnecessary genes responsible for aerobic respiration and become an even simpler organism. Evolution can go in strange directions,” marvels Israeli zoologist Dorothee Hutchon.


Ishi Nobu, The Web of Life, BookBaby (2019).

Dayana Yahalomi et al, “A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome,” PNAS (24 February 2020).

Michael Le Page, “Animal that doesn’t need oxygen to survive discovered,” Science News (24 February 2020).

Biologists discover animal that lacks mitochondrial genome, doesn’t need oxygen to live,” Sci News (26 February 2020).