Question
Prepare a comparison table showing the major phyla of the Animal Kingdom, with key distinguishing features for each phylum.
Solution — Step by Step
Animals are classified based on several criteria:
- Body symmetry: radial vs bilateral vs asymmetrical
- Coelom: acoelomate (no body cavity), pseudocoelomate (false cavity), coelomate (true cavity)
- Germinal layers: diploblastic (2 layers: ectoderm + endoderm) vs triploblastic (3 layers: ecto + meso + endo)
- Notochord: present or absent (distinguishes Chordates)
- Segmentation: present or absent
| Phylum | Examples | Symmetry | Coelom | Special Features |
|---|---|---|---|---|
| Porifera | Sponges | Asymmetrical | Absent | Pores (ostia) and canal system; spicules; most primitive |
| Coelenterata (Cnidaria) | Hydra, Jellyfish, Coral | Radial | Absent | Diploblastic; stinging cells (cnidocytes/nematocysts); gastrovascular cavity |
| Platyhelminthes | Planaria, Tapeworm, Liver fluke | Bilateral | Acoelomate | Triploblastic; flat body; flame cells for excretion |
| Nematoda | Roundworms, Ascaris | Bilateral | Pseudocoelomate | Cylindrical, unsegmented; cuticle; no circulatory system |
| Annelida | Earthworm, Leech, Nereis | Bilateral | True coelomate | Segmentation (metameric); setae; closed circulatory system |
| Arthropoda | Insects, Spiders, Crabs, Prawns | Bilateral | True coelomate | Exoskeleton (chitin); jointed appendages; largest phylum |
| Mollusca | Snails, Octopus, Oysters, Squid | Bilateral | True coelomate | Soft body; mantle; radula (except bivalves) |
| Echinodermata | Starfish, Sea urchin, Sea cucumber | Radial (adult) | True coelomate | Water vascular system; spiny skin; deuterostomes |
| Chordata | Fish, Frog, Lizard, Birds, Mammals | Bilateral | True coelomate | Notochord; dorsal hollow nerve cord; pharyngeal gill slits |
Within Chordata, vertebrates are classified into five major classes:
| Class | Body temperature | Skin | Respiration | Examples |
|---|---|---|---|---|
| Pisces (Fish) | Cold-blooded | Scales | Gills | Rohu, Shark |
| Amphibia | Cold-blooded | Moist, no scales | Gills (larva), lungs + skin (adult) | Frog, Salamander |
| Reptilia | Cold-blooded | Dry scales | Lungs | Snake, Lizard, Crocodile |
| Aves (Birds) | Warm-blooded | Feathers | Lungs with air sacs | Pigeon, Crow |
| Mammalia | Warm-blooded | Hair/fur | Lungs | Dog, Bat, Whale, Human |
Why This Works
Classification is based on shared derived characteristics (synapomorphies) that indicate evolutionary relationships. Organisms sharing more characteristics are more closely related.
The trend from simpler to more complex organization: Porifera (no tissues) → Coelenterata (tissue level) → Platyhelminthes (organ level) → advanced phyla (organ system level).
Common Mistake
Students confuse “acoelomate” and “pseudocoelomate.” Acoelomate animals (Platyhelminthes) have NO body cavity between the body wall and gut. Pseudocoelomates (Nematoda) have a cavity but it’s not lined by mesoderm on both sides. True coelomates (Annelida onwards) have a body cavity lined by mesoderm on all sides. The distinction matters for NEET objective questions.