Some plankton rotifers like Brachionus are are used as diet in aquaculture, s but aside from this also in natural habitats there are some invertebrate and even unicellular organisms that can feed on rotifers. There are even rotifers that feed on other rotifers. Even cannibalism has been observed in species like Asplanchna. The feeding behavior of the predators can in most cases only be concluded from the hard parts of the rotifer´s mastax, the chitinous trophi, which cannot be digested by the predator.
Some species of tardigrades feed on rotifers, but unfortunately up to now I could not find any traits for this.
rotifers as predators of rotifers
monogonont rotifers
It is not uncommon that rotifers feed on other rotifers. Most of the predators are monogonont rotifers, but also some bdelloid rotifers are predators, e.g. Abrochtha carnivora (a species I could not find so far).
Vice versa: Cephalodella gibba (left) with trophi of Encentrum sp. In this example Cephalodella is the predator and Encentrum is the prey. Right: Encentrum gulo shortly after swallowing a Cephalodella rotifer (arrowheads). (right).
There are only a few bdelloid rotifers. One is Abrochtha carnivora; and there is one Philodina reported to be a predator as well.
canibalism
During a growing season the specimens of Asplanchna tend to get bigger and bigger so that it gets more likely that a specimen can attack and swallow a member of the same species. Cannibalism has been reported of Asplanchna sieboldi, but up to now could I could not observe such an event. The extensions on the integument of this Asplanchna sieboldi specimen are concieved as an adaptation to withstand the cannibalism by members of the same species.
