Question

Snails and insects belong to which group of organisms?

Answer 1

Snails and insects are both invertebrates. The invertebrates are distributed among 9 phylum- Porifera, Cnidaria, Ctenophora, Platyhelminthes, Aschelminthes, Annelids, Arthropoda, Mollusca, Echinodermata. Insects are the most diversified group of organisms present on this planet. It is estimated that 5.5 million insect species are present all over the world.

Complete answer:
The insects fall under the phylum Arthropoda. The Arthropoda is the largest phylum harboring the most diversified species. Few characters of the phylum are:
1. Jointed legs connected with the arthrodial membrane.
2. Body is covered with a chitinous exoskeleton.
3. Open circulatory system is found.
4. No respiratory pigment is found in the hemolymph or haemocoelomic fluid.
5. Development may be direct (Silverfish, prawn) or indirect (includes larval stages as in butterfly).
The snails fall under the phylum Mollusca. Few characters of this phylum are:
1. Soft, unsegmented body.
2. Locomotive organ is muscular feet.
3. Body differentiated into 3 distinct parts- head, a visceral mass, and ventral foot.
4. Visceral organ is covered with a mantle membrane.
5. In their digestive system, a special type of rasping organ radula is present, which helps in grinding of food.
The snails have a shell at their back made up of calcium carbonate and conchiolin protein.
The snails are accommodated to both aquatic and terrestrial environments. Insects are also found in both the habitats.

Note:
An important information that can be noted in respect of both these phylums is that of the connecting links. The connecting links are organisms that cannot be placed in any of the two concerned phylums that it represents since it shares common characteristics from both the phylums. These organisms are therefore studied from the evolutionary aspect.
The connecting link between phylum Arthropoda and phylum Mollusca is Neopilina. It is known as segmented mollusc. The segmentation is a characteristic of phylum Arthropoda whereas it shares many characteristics of Mollusca as well.