#micrognathozoa

Xenacoelomorpha: Small, flat, worm-like animals that live in marine and brackish sediments, and sometimes around hydrothermal vents. They can be free-living, symbiotic, or parasitic. A unique feature is that their stomachs lack nerve cells, unlike many other animals. Their evolutionary relationship to the rest of Animalia has been highly debated, and very little is known about their lifestyles.

(sources - 1, 2, 3)

Remember when I said Cycliophora was the newest descriped phylum? I lied. I was a fool.

The real newest described phylum, only described in 2000, is Micrognathozoa. It is so new that it only contains one species, Limnognathia maerski, which was once considered a rotifer.

With an average length of 100 micrometers, Limnognathia is one of the smallest known animals. Yet, it has very complex jaws and a brain! The animal can extend part of its jaw structure outside its mouth while eating or regurgitating. It has cilia for moving food towards its mouth, as well for moving itself and for sensing its environment. It feeds on bacteria, blue-green algae, and diatoms. All adults studied so far have had female organs, yet some of the youngest individuals collected seemed to have male organs, suggesting they change sex with age. They lay two kinds of eggs: thin-walled eggs that hatch quickly, and thick-walled eggs that may be resistant to freezing and thus intended to overwinter and hatch in the Spring.

Discovered in 1994 in the cold springs of Disko Island, Greenland, Limnognathia has since been found in other cold areas including Antarctica and the British Isles. There are likely more species yet to be described.

Propaganda under the cut:

Chordata: All animals with a backbone (Vertebrata), but also some invertebrates. Chordata includes fish, birds, mammals, reptiles, and amphibians, but also sea squirts and lancelets. All Chordates have a notochord (supportive rod-like structure), a hollow dorsal nerve cord, pharyngeal slits (for filter feeding/breathing), a post-anal tail, and an endostyle (feeding organ) or thyroid (hormonal gland). Interestingly, many Chordates have overcome the need to raise their young in water by laying shelled eggs or carrying young within the womb. Fur, feathers, and scales are all unique adaptations found within Chordata. This phylum exhibits remarkable diversity overall.

This means that this tiny organism, this entire phylum, has a potentially worldwide distribution… and we didn’t even discover it until 1994.

-micrognathozoa boss