The invertebrates are usually classified as Lower Invertebrates and Higher Invertebrates.
- The lower invertebrates are simple in body organization.
- They are generally small in size.
- These are thought to have originated in the main lines of evolution, near the base of the phylogenetic tree of Animal kingdom.
- Lower Invertebrates includes Protozoa, Porifera, Coelenterata (Cnidaria), Platyhelminthes and Nematoda.
- They possess a complex body organization.
- They are generally larger in size.
- These occupy a higher position in the phylogenetic tree of Animal kingdom.
- Higher Invertebrates include Mollusca, Annelida, Arthropoda, and Echinodermata.
On the basis of some important features, there are some differences between lower and higher invertebrates as shown below:
Table 1: Differences between Lower Invertebrates and Higher Invertebrates
|1.||Size||Smaller in size||Larger in size|
|2.||Body organization||Body organization simple||Body organization complex|
|3.||Symmetry||Radial, biradial or no symmetry||Bilateral symmetry|
|4.||Germ Layers||Germ layers wanting or 2 or 3 germ layers||Three germ layers present|
|5.||Coelom||No Coelom or a pseudo-coelom||True Coelom|
|6.||Mouth and Anus||Generally, no separate mouth and anus||Mouth and Anus are separate|
|8.||Blood Vascular System||Not well developed||Well developed|
- Kotpal RL. 2017. Modern Text Book of Zoology- Invertebrates. 11th Edition. Rastogi Publications.
- Jordan EL and Verma PS. 2018. Invertebrate Zoology. 14th Edition. S Chand Publishing.