question_answer 76)

  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:

  The organisms here do not belong to the same group. Leech and Nereis belong to phylum-Annelida while, Scolopendra, prawn and scorpion belong to phylum-Arthropoda. The distinguishing factors of both the phylums are given below

Annelids (Latin, annlus-ring; lidos-form)	Arthropods (Greek, arthro-ointed; podos-foot)
1. These are triploblastic animals having bilaterally   symmetrical,   elongated, vermiform, cylindrical or dorsoventrally	1.   These are triploblastic, bilaterally symmetrical and segmented animals.
2. Annelids a.re the first animals to develop True body cavity or coelom.	2. Body cavity is filled with blood, i.e., haemocoelic and have open circulatory system, so the blood does not flow in blood vessels. Excretion takes place by Malpighian tubules (insects) and green glands (crab and prawn). In many arthropods, compound eyes are present with mosaic vision.
3. The differentiation occurs-in a segmental fashion, with the segments !ined up one after the other from head to tail (metameric segmentation).	3. Body segments are grouped into two regions, i.e., cephalothorax (head and thorax together) and abdomen or three region, i.e., head, thorax and abdomen. Body segment of these animals (somite) usually bears paired lateral and jointed legs or appendages. Muscular system with exoskeleton for attachment is present. Gilia are absent.
4. Their sexes may be hermaphroditic or separate.	4. Fertilisation is usually internal, oviparous or ovoviviparous often with metamer sexes are usually separate.
5. Locomotion is done with the segmentally arranged paired lateral appendages, parapodia or chitinous setae or chaetae. They respire through skin.	5. Respiration is through general body surface, by gills, air tubes (tracheae) or book lungs