| Presence of notochord |
Absent or rudimentary structure called a stomochord |
Notochord present, typically as a flexible rod-like structure supporting the body. |
| Nervous system |
Simple, with a nerve net |
More complex, with a dorsal hollow nerve cord |
| Gill slits |
Present, used for filter-feeding in some species |
Present, often used for filter-feeding or respiration |
| Post-anal tail |
Absent |
Present in at least some stage of the life cycle |
| Segmentation |
Generally absent in adults |
Present in some groups e.g., vertebrates |
| Circulatory system |
Simple, often with a tubular heart |
More complex, with a chambered heart in many species |
| Pharyngeal slits |
Present but not considered true gill slits |
Present, and may function in feeding or respiration |
| Notocord development |
In some species, the stomochord may persist throughout life |
Develops into the vertebral column in vertebrates |
| Body shape |
Worm-like in appearance |
Complex body plans, including fish, mammals and humans |
| Dorsal hollow nerve cord |
Generally absent |
Present, runs along the dorsal side of the body |
| Examples
|
· Acorn worms (Enteropneusta)
· Pterobranchs
|
· Fishes
· Amphibians
· Reptiles
· Birds
· Mammals
|
