Convolutriloba retrogemma

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Convolutriloba retrogemma
Underside of Convolutriloba retrogemma on aquarium pane, length approx. 3 mm

Underside of Convolutriloba retrogemma on aquarium pane, length approx. 3 mm

Empire : Animals (Animalia)
Trunk : Xenacoelomorpha
Class : Acoela
Family : Convolutidae
Genre : Convolutriloba
Type : Convolutriloba retrogemma
Scientific name
Convolutriloba retrogemma
Hendelberg & Åkesson , 1988

Convolutriloba retrogemma is a reddish-brown, a few millimeters long, predatory , marine Acoel which among other small crustaceans , polychaetes and rotifers eat and so far only from seawater aquarium with coral is known.


Convolutriloba retrogemma has a planarian shape with a thin and wide, leaf-shaped, reddish-brown body. The largest individuals are about 6 mm long and 5.5 mm wide. At the front of the body are two unpigmented eyes. The animal shows a positive phototaxis and turns as much body surface as possible towards the light. When prey is disturbed or approached, it stretches and folds its side edges downwards so that only these touch the ground when moving. When prey is caught, the front end of the body is expanded into a funnel-shaped hood and the prey is completely enclosed or pressed against the ground. Like other acoela, Convolutriloba retrogemma does not have an intestinal cavity, but a centrally located, spherical, approximately 0.3 mm large mass of endodermal cells that are rearranged when the prey is devoured into a sack-shaped stomach, which bulges upwards when the prey is large.


Convolutriloba retrogemma eats in laboratory experiments quickly floating copepods , brine shrimp larvae, small polychaete and rotifers . When prey approaches, the ambulance hunter forms his hood at the front and pulls it over the victim in one quick movement. Up to 7 Artemia larvae fit into the temporary stomach of a Convolutriloba retrogemma. The predator's reproductive rate is much higher after eating crabs than after eating polychaetes alone.

The animal lives in an obligatory symbiosis with unicellular green algae , from whose photosynthetic products they live exclusively if no prey animals are available. The animal is therefore dependent on light. The algae are distributed all over the body with the exception of small areas around the unpigmented eyes. Parts of the algae population are digested by the stomach cells. If the animal dies, large quantities of the green algae cover the carcass.

Experiments with starvation without prey and on the other hand without light suggest that Convolutriloba retrogemma is dependent on both diets at the same time for a successful reproduction in the long term.

Life cycle

Convolutriloba retrogemma reproduces asexually by budding , whereby endosymbiotic green algae are concentrated in the buds. The buds are pinched off at the rear end, with the heads of the young animals being turned backwards, i.e. 180 ° to the body axis of the mother animal (reverse polarity).

Convolutriloba retrogemma is a simultaneous hermaphrodite with ovaries , testicles and both female and male reproductive organs. So far, however, there is no description of sexual reproduction in Convolutriloba retrogemma .

distribution and habitat

The natural habitat and range of Convolutriloba retrogemma are unknown. The animal is often observed in tropical marine aquariums with corals , where it is undesirable due to its often massive reproduction. Toxins emitted by the animal for protection can damage or kill other aquarium inhabitants such as corals or fish.


The most important known predator of Convolutriloba retrogemma is the variable head shield snail ( Chelidonura varians ), which, as a food specialist, feeds exclusively on these prey animals. It is therefore kept in saltwater aquariums, but starves to death when all the Convolutriloba retrogemma have been eaten.


  • Jan Hendelberg, Bertil Åkesson (1988): Convolutriloba retrogemma gen. Et sp. n., a turbellarian (Acoela, Platyhelminthes) with reversed polarity of reproductive buds. Advances in Zoology 36, pp. 321–327.
  • Bertil Åkesson, Jan Hendelberg (1989): Nutrition and asexual reproduction in Convolutriloba retrogemma, an acoelous turbellarian in obligate symbiosis with algal cells. In: JS Ryland, PA Tyler (Ed.): Reproduction, genetics and distributions of marine organisms. Olsen & Olsen, Fredensborg (Danmark) 1989, pp. 13-21.
  • Bertil Åkesson, Robert Gschwentner, Jan Hendelberg, Peter Ladurner, Johann Müller, Reinhard Rieger (2001): Fission in Convolutriloba longifissura: Asexual reproduction in acoelous turbellarians revisited. Acta Zoologica 82, pp. 231-240. doi: 10.1046 / j.1463-6395.2001.00084.x . ISSN 1463-6395.

Web links

Individual evidence

  1. Thomas Bartolomaeus, Ivonne Balzer (1997): Convolutriloba longifissura, nov. spec. (Acoela) - first case of longitudinal fission in Plathelminthes. Microfauna Marina 11, pp. 7-18.
  2. Reefkeeping Magazine -. Flatworms and Other "bugs" That Make You See Red Accessed on June 16, 2018.