Reinhardt Kristensen was born in Brande, Denmark in 1948. He is famous for discovering several microscopic organisms, and for his expertise on tardigrades. His recent research focuses primarily on arctic biology.
In 1983, Kristensen discovered the Loricifera, a phylum of marine sediment-dwelling animals, off the coast of France. These creatures were first found in the spaces between sand and shell gravel, but they have since been shown to inhabit diverse environments across all latitudes, including muddy substrates, seamounts, and the deep sea. They are particularly elusive because of their patchy distribution, and the fact that they adhere strongly to the sediment grains between which they live. They secrete a protective, armor-like casing, known as their “lorica”. Deep-sea species of Loricifera are the first multicellular organisms known to spend their entire life cycle in permanently anoxic conditions, using a specialized organelle instead of mitochondria to generate energy. The Loricifera is pretty picky about where it lives. While we don’t quite understand its criteria for choosing its habitats, we do know that Loriciferans do not dedicate any stages in their life cycle to dispersal.
Still, if you thought the Loricifera inhabited obscure places, you haven’t heard anything yet. In 1995, Reinhardt uncovered a microscopic aquatic animal with a complicated life cycle, called Symbion pandora. These jug-shaped creatures exclusively inhabit lobster mouths, scavenging debris from their hosts’ meals.
Their commensal symbiosis with the lobster inspired their genus name, Symbion. The word pandora comes from Pandora’s Box in Greek mythology, and refers to the creature’s form during its sessile feeding phase, which contains an inner bud and a larva with its own feeding stage. Symbion pandora have an extraordinarily complicated life cycle that alternates between sexual and asexual stages. For a fun lesson on the life cycle of Symbion, watch this CreatureCast video by Nati Chen.
Because the Symbion have such distinct features, Kristensen and his colleagues assigned them to their own phylum, Cycliophora. This became the first new phylum of metazoans to be established since Kristensen’s discovery of the Loricifera twelve years earlier.
In 2000, not long after the discovery of Symbion pandora, Kristensen and Funch struck gold again, becoming the first scientists to describe Micrognathozoa, the most esoteric animal of all. Indeed, Micrognathozoa have only ever been found in one single, frigid lake in Greenland. During a field course excursion to Disko Island in Greenland, Kristensen and Funch uncovered the creature in a cold spring near Isunngua on the eastern part of the island.
Micrognathozoa have intricate jaws that contain 32 moving parts, some of which can extend to facilitate the feeding process. Only female Micrognathozoan specimens have ever been collected; scientists theorize that the animals may hatch as males and later change into females.
Why I Admire Kristensen:
These animals remind us that the world is teeming with millions of unique organisms – from tardigrades, which rain down from the stratosphere in abundance; to the Loricifera, which can live in some of the most extreme, anoxic conditions on Earth; to the Symbion and Micrognathozoa, which have remarkably specific requirements for where they make their home. Thanks to Reinhardt Kristensen — intrepid explorer of the animal kingdom — we have a tiny bit more knowledge of our planet and its rich abundance of life.