Placozoan species Hoilungia hongkongensis . Credit: Hans-Jürgen Osigus, Stiftung Tierärztliche Hochschule Hannover Placozoans, some of the simplest animals in the world, are found in coastal waters globally. These tiny organisms, only a few millimeters in size, were once thought to inhabit either solid surfaces—like rocks, corals, and mangrove roots—or to drift in open coastal waters in their “swarmer” stages.
Through analysis of DNA traces in the stomachs of predatory sea slugs, a team led by LMU geobiologist Professor Gert Wörheide has demonstrated that the animals also live in the seabed sediment, a habitat they were previously thought not to colonize. In addition, they are more genetically diverse than had been known, as the researchers report in the journal Ecology and Evolution . With their flat, disk-shaped bodies, all placozoans worldwide look strikingly similar.
Nevertheless, Wörheide and his team have already demonstrated in previous studies that there are huge genetic differences between them. “These differences are comparable with those between humans and mice,” emphasizes the geobiologist. Due to their diminutive size and inconspicuousness, placozoans are challenging to study in their natural environments.
To gain a better insight into the ecology of the animals, the researchers exploited the fact that small shell-less sea slugs from the Rhodopidae family feed on placozoans. Prof. Gert Wörheide investigated publicly accessible genetic data f.