Let me share with you difference between acoelomata, pseudocoelomata and coelomota.
| Aspect | Acoelomata | Pseudocoelomata | Coelomata |
| Coelom | Absent | Pseudocoelom | True coelom |
| Coelomic cavity | Absent | Pseudocoelomic cavity | True coelomic cavity that is completely lined with mesoderm |
| Layers | Diploblastic (ectoderm and endoderm) | Triploblastic (ectoderm, mesoderm, and endoderm) | Triploblastic (ectoderm, mesoderm and endoderm) |
| Body Wall | Cellular mesenchyme | Muscle cells under epidermis | Muscular and connective tissue layers |
| Movement | Ciliary gliding | Muscular movement by pseudocoelomic fluid | Muscular movement by coelomic fluid |
| Excretory System | Protonephridia or flame cells | Excretory tubules without specialized cells | · Metanephridia · Malpighian tubules |
| Examples | · Flatworms e.g., Planarians | · Roundworms e.g., Nematodes | · Annelids · Arthropods · Chordates |