Question

You are given leech, Nereis, Scolopendra, prawn and scorpion; and all have segmented body organisation. Will you classify them in one group? If no, give the important characters based on which you will separate these organisms into different groups.

Answer 1

No, we will not classify all the given organisms in one group because there are some characteristic features by which these organisms can be separated from each other and placed in two different group.
Leech and Nereis are placed in Phylum Annelida because:

1. (i) Both of these have metamerically segmented body i.e. body is divided internally into many segments by septa. Body segments are lined up one after the other from head to tail.
2. (ii) These animals have a closed circulatory system.
   Scolopendra, Prawn, and scorpion are placed in Phylum Arthropoda because :
   • Their body is externally segmented and consists of the head thorax and abdomen.
   • These animals have an open circulatory system and the coelomic cavity is blood-filled called hemocoel.