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| Character | *Echinodermata* | *Hemichordata* | *Mollusca* |
| ------------------------- | ------------------------------------------------ | --------------------------------------------- | ------------------------------------------------------- |
| *Habitat* | Exclusively marine | Marine | Mostly marine, some freshwater & terrestrial |
| *Level of organisation* | Organ system level | Organ system level | Organ system level |
| *Symmetry* | Radial (pentamerous in adults); bilateral larvae | Bilateral symmetry | Bilateral symmetry |
| *Germ layers* | Triploblastic | Triploblastic | Triploblastic |
| *Body cavity* | True coelom | True coelom | True coelom |
| *Segmentation* | Absent | Absent | Absent |
| *Body form* | Star-shaped or globular | Worm-like body | Soft, unsegmented body |
| *Special feature* | Water vascular system present | Body divided into proboscis, collar and trunk | Body divided into head, muscular foot and visceral mass |
| *Skeleton* | Endoskeleton of calcareous ossicles | No true skeleton | Shell usually present (calcareous) |
| *Respiration* | Through tube feet or dermal branchiae | Through gill slits | Through gills (ctenidia) or lungs |
| *Circulatory system* | Reduced or absent | Open circulatory system | Open circulatory system |
| *Excretion* | Absent | Proboscis gland | Nephridia |
| *Examples* | Starfish, Sea urchin, Brittle star | Balanoglossus, Saccoglossus | Pila, Octopus, Unio

*NEET Tip*

*Water vascular system → Echinodermata*
*Proboscis–collar–trunk → Hemichordata*
*Mantle & shell → Mollusca*