AIIMS 2019 Zoology Platyhelminthes MCQ Question

Correct Answer: A) Platyhelminthes

Explanation: Platyhelminthes, commonly known as flatworms, are known for their parasitic forms such as tapeworms (Cestoda) and flukes (Trematoda). These organisms exhibit specialized structures such as hooks and suckers that allow them to attach to the host's tissues and absorb nutrients directly from the host's digestive system.

1. Hooks and Suckers: These adaptations are crucial for their survival as endoparasites, enabling them to anchor securely to the intestinal walls of their hosts.
2. Endoparasitic Lifestyle: Many species within this phylum are obligate endoparasites, meaning they live inside the bodies of their hosts, relying on them for sustenance and reproduction. Examples include:
   • Tapeworms (Cestoda): Have a scolex (head) with hooks and suckers that help them adhere to the intestines of vertebrates.
   • Flukes (Trematoda): Often have oral and ventral suckers to attach to their hosts.

Why Other Options are Incorrect:

B) Annelida: Annelids are segmented worms, which include earthworms and leeches. While some leeches are parasitic, they do not possess hooks; instead, they use a combination of suckers and their segmented bodies for movement and attachment. They are not primarily endoparasites; most are free-living or ectoparasitic.

C) Ascheminthes (more commonly known as Nematoda): Nematodes, or roundworms, do have parasitic members, but they do not typically possess hooks and suckers. They may have other structures for attachment, but these are not the same as the hooks and suckers found in Platyhelminthes. Many nematodes are endoparasites, such as those that infect plants and animals, but the specific features described in the question align more closely with flatworms.

D) Arthropoda: Arthropods are a diverse group including insects, arachnids, and crustaceans. While some arthropods can be ectoparasites (like ticks and fleas), they do not have hooks or suckers in the context described. Their attachment strategies are fundamentally different, relying on mouthparts and other adaptations rather than hooks and suckers.

Summary:

Given this analysis, the correct answer is indeed A) Platyhelminthes. These organisms are characterized by their flat bodies, hooks, and suckers, which are essential for their parasitic lifestyle. The other options do not fulfill the criteria specified in the question regarding hooks and suckers as adaptations in endoparasitic life forms.