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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
Scientific name
Hendelberg & Åkesson , 1988

Convolutriloba is a genus of predatory marine acoela with four known species , which, with one exception, are only known from marine aquariums.


The Acoela of the genus Convolutriloba have thin, shield-shaped, planar-like bodies with three lobes at the end of the body. The animals are a few millimeters, at most 1 cm long, a few millimeters wide and less than 1 mm thick. They have two unpigmented eyes at the front end of their body and, as sexually produced young animals, also have a statocyst , which is missing in adult animals. Sagittocysts, about 18 to 50 µm long, needle-shaped structures, which presumably serve to capture and defend prey and which are also present in the genera Antrosagittifera , Praesagittifera , Sagittifera and Symsagittifera , sit in the skin . The animals feed in two ways: On the one hand, they harbor symbiotic green algae ( zoochlorella ), which give them a green or brown color, and therefore show positive phototaxis . On the other hand, they prey on small animals, especially small crustaceans , which they enclose with a funnel-shaped hood at the front end of the body and press into the body through the mouth opening on the underside of the body. Like other acoela, the representatives of Convolutriloba do not have an intestinal cavity, but a mass of endodermal cells that are rearranged into a bag-shaped stomach to digest the prey.

The animals are simultaneous hermaphrodites that reproduce both sexually and asexually. They lay eggs in large numbers, from which small, still algae-free young animals develop. These have to absorb green algae as symbionts within a few weeks in order not to starve. Asexual reproduction takes place through budding, with the heads of the young animals being turned backwards, i.e. 180 ° to the body axis of the mother animal (reverse polarity), or through autotomy without prior differentiation of the internal organs ( architomy ). During asexual reproduction, endosymbiotic green algae are always passed on to the young animals.


  • Convolutriloba hastifera (Winsor, 1990) is the only one of the four speciesthat has been isolatedfrom its natural habitat, the coral reefs on the Australian island of Magnetic Island . The species is characterized by an architomy made transversely , in which a hardly differentiated smaller fragment is torn off by holding on to the substrate and grows into a whole animal within a few days.
  • Convolutriloba longifissura (Bartolomaeus & Balzer, 1997) is only known from saltwater aquariums. It reproduces asexually through architomy, in that a butterfly-shaped body is torn off at the rear end, which in turn splits into two daughters, so that after an architomy process there are three individuals.
  • Convolutriloba macropyga (Shannon & Achatz, 2007) is also only known from saltwater aquariums. This species is noticeable for its intense green color and a double-sided notch on the head. Asexual reproduction occurs by budding with reverse polarity on the lobes of the end of the body.
  • Convolutriloba retrogemma (Hendelberg & Akesson, 1988) is also only known from saltwater aquariums. The individuals of this species are reddish-brown in color. Asexual reproduction occurs by budding with reverse polarity on the lobes of the end of the body.


  • 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.
  • Thomas Shannon, Johannes G. Achatz (2007). Convolutriloba macropyga sp. nov., an uncommonly fecund acoel (Acoelomorpha) discovered in tropical aquaria. Zootaxa 1525, pp. 1-17. ISSN 1175-5326.
  • Robert Gschwentner, Peter Ladurner, Willi Salvenmoser, Reinhard Rieger, Seth Tyler (1999): Fine Structure and Evolutionary Significance of Sagittocysts of Convolutriloba longifissura (Acoela, Platyhelminthes). Invertebrate Biology 118 (4), pp. 332-345.