Question

Which of the following animals does not have a body composed of many segments?
(a) Flatworm
(b) Grasshopper
(c) Earthworm
(d) Lobster

Answer 1

Hint: Metameric segmentation is basically the repetition of organs and tissues at several intervals along the body of an animal, thus dividing the body into segments (metameres).

Complete answer:
Annelids are characterized as triploblastic, bilaterally symmetrical, metamerically segmented, coelomate, and have a thin flexible cuticle around the body. On the other hand, arthropods are invertebrate animals that have an exoskeleton, a segmented body, and jointed appendages.
It is seen that both arthropods and annelids have segmented bodies. Additionally, these segments have become specialized with one pair of jointed appendages added to each segment.
Phylum Platyhelminthes is mainly composed of flatworms. Animals under this category are acoelomate organisms that also include many free-living and parasitic forms. They are also characterized as triploblastic, bilaterally symmetrical, dorsoventrally flattened, acoelomate flatworms with organ grade of construction. They lack a definite anus, circulatory, skeletal or respiratory system.

Additional information: Some facts about arthropods are as follows:
- It is known that Arthropods colonized land about 100 million years before vertebrates did because colonizing land was easier for them as they had already evolved legs, which they used for walking on the sea bed.
- Nearly $80\%$ of all animal species are arthropods!
- All arthropods undergo a metamorphosis which is a process where their bodies change radically as they pass from their larval to adult stages.
- Crustaceans and arachnids are the two types of arthropods that have blue blood instead of red blood! This is because their blood uses a blue copper compound to carry oxygen, instead of the red iron compound used by animals.
- Annelids don’t possess lungs and they receive oxygen through their skin!
- Annelids can vary from a length of 1 millimeter to over 3 meters long!
So, the correct answer is ‘(a) Flatworm’.

Note: The phylum comprises four basic classes: Trematoda (flukes), Cestoda (tapeworms), Turbellaria (planarians), and Monogenea. All the members belonging to this phylum are parasitic, except Turbellaria during all or part of the life cycle.