Body of an organism that otherwise lacks substantial into distinct tissues.

, , , , and some of the more are better described as possessing thalli for bodies. See also the concept of .

Another way of describing these organisms is that they all lack a level of body organization, instead possessing a (i.e., cellular differentation, but not substantial organization of those cells into distinct tissues). Though not described in terms of possessing a thallus, nonetheless see equivalently the sponges.