Table : table 31.1 Anatomical Characteristics of Some Major Protostome Groups
| Group | Body cavity | Digestive tract | Circulatory system |
|---|
| Arrow worms | Coelom | Complete | None |
| Lophotrochozoans | | | |
| Bryozoans | Coelom | Complete | None |
| Entoprocts | None | Complete | None |
| Flatworms | None | Blind gut | None |
| Rotifers | Pseudocoel | Complete | None |
| Gastrotrichs | Pseudocoel | Complete | None |
| Ribbon worms | Coelom | Complete | Closed |
| Brachiopods | Coelom | Complete in most | Open |
| Phoronids | Coelom | Complete | Closed |
| Annelids | Coelom | Complete | Closed or open |
| Mollusks | Reduced coelom | Complete | Open except in cephalopods |
| Ecdysozoans | | | |
| Nematodes | Pseudocoel | Complete | None |
| Horsehair worms | Pseudocoel | Greatly reduced | None |
| Arthropods | Hemocoel | Complete | Open |