They are called acelomates (their scientific name is Acoelomata) to the edges of bilateral animals lacking of general cavity; therefore, present a massive body since between the wall of the body and the intestine there is a mass of cells (mesenchyme) and muscle fibers. The term acelomado lacks any taxonomic meaning.
The typically acelomados cuttings are Platelmintos and Nemertinos; Mesozoans are also often considered as acelomates, although their phylogenetic relationships are still obscure. The rest of the bilaterals have (at least in the embryonic state) a body cavity filled with fluid between the wall of the body and the intestine, either a real coelom (celomates) or a pseudocelloma (Pseudocelomados or Blastocelomados).
The acelomates are the simplest bilateral, with vermiform bodies and ciliated epithelia, and most zoologists agree that the origin of the bilaterals passes through an acellomated ancestor from which the turbelarios and the first coelomates would arise (see Bilateria for other theories). Therefore, they would be the group from which the radiation of all triblástica animals derives. It is very light and smooth the body acelloma Bibliography
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