Let me share with you a difference between grade radiata and grade bilateria.
| Aspect | Grade Radiata | Grade Bilateria |
| Symmetry | Radial symmetry | Bilateral symmetry |
| Complexity | Less complex | More complex |
| Tissue organization | Tissues organized around a central axis | Tissues organized into distinct germ layers (ectoderm, mesoderm, and endoderm) |
| Cephalization | Absent or minimal | Well-developed head region |
| Nervous system | Simple nerve net | Concentrated nerve ganglia, often with a brain |
| Germ layers | Diploblastic (ectoderm and endoderm) | Triploblastic (ectoderm, mesoderm, endoderm) |
| Body openings | Single opening (e.g., gastrovascular cavity) | Two openings (mouth and anus) or complete digestive system |
| Segmentation | Often lack segmentation | Segmentation present or absent depending on the group |
| Embryonic development | Indeterminate cleavage | Determinate cleavage |
| Fate of blastopore | Forms either mouth or anus | Forms either mouth or anus, depending on the group |
| Movement | Often slow, with radial symmetry | More agile and directed movement with bilateral symmetry |
| Examples | · Cnidaria e.g. jellyfish and corals · Ctenophora e.g. comb jellies |
· Chordata,
· Arthropoda · Mollusca, etc. |