can be used for diffusion of gases and metabolites etc. These creatures do not have this need, as the surface area to volume ratio is large enough to allow absorption of nutrients and gas exchange by diffusion alone, due to dorso-ventral flattening. Platyhelminthes Gastrotricha, traditionally viewed as blastocoelomates Entoprocta, traditionally viewed as blastocoelomates Gnathostomulida, traditionally viewed as blastocoelomates Cycliophora According to others, acoelomates include the cnidarians (jellyfish and allies), and the ctenophores (comb jellies), platyhelminthes (flatworms including tapeworms, etc.), Nemertea, and Gastrotricha. * See also Abdominal cavity References Further reading Animal anatomy Animal developmental biology Mesoderm