Ytrötmidae

The Ytrötmidae are a hypothetical family of marine invertebrates, proposed in speculative zoological literature. While no living or fossil specimens have ever been scientifically documented, the concept of Ytrötmidae typically describes organisms possessing a radially symmetrical, gelatinous body structure, often with multiple feeding appendages. Their proposed habitat is the deep ocean, where they are imagined to be sessile or slow-moving filter feeders.

The internal anatomy, as envisioned by theorists, often includes a simple digestive system and a decentralized nervous system. Reproductive strategies are also speculative, with possibilities ranging from asexual budding to broadcast spawning. The evolutionary lineage of Ytrötmidae, if they existed, is unclear, with some hypotheses placing them as early offshoots of cnidarians or ctenophores, while others suggest a more distant, independent origin.

The term "Ytrötmidae" itself is a neologism, created for the purpose of theoretical discussion. The concept serves as a placeholder for potential, undiscovered life forms that might occupy ecological niches not currently understood by science. Further exploration of extreme marine environments is sometimes cited as a potential avenue for discovering organisms that might fit such a description, though no concrete evidence supports the existence of this specific taxonomic group.