Question

From the following specification, identify the phylum the animal belongs to.
Triploblastic unsegmented, acoelomate, exhibiting bilateral symmetry, and reproducing both asexually and sexually, with parasitic forms.
(a) Porifera
(b) Platyhelminthes
(c) Annelida
(d) Ctenophora

Answer 1

Hint Animals with an unsegmented body plan are generally flat and cylindrical with or without a digestive tract. Triploblastic animals show all the three germ layers with a definite organ system.

Complete Answer:
Platyhelminthes are flat and ribbon-like worms also known as a flatworm. They are free-living terrestrial, freshwater, or marine form which is mostly parasitic on other animals. They show an organ system level of organization with all the three germs layers. They are the first triploblastic animal. The body plan is a blind sac body plan with the head at the anterior end. It has a brain and sense organs in the head which remain forward during locomotion. Body surface consists of cilia for locomotion and lateral appendages are completely absent. The body wall consists of single-layered epidermis and muscle layers, each cell lies near the external body surface and internal digestive cavity. They are acoelomate animals without a body cavity. Space between the body wall and cavity is filled with parenchyma and mesenchymal. Skeletons are absent but cuticles present on the outer surface maintain body form. The digestive tract may be complete or incomplete with the branched digestive cavity. Respiration occurs through the body surface. Excretion occurs through the flame cell which works as a kidney. They are generally hermaphrodite and show cross-fertilization. They are viviparous animals including one or more larval stages. Asexual reproduction also is shown by some form that takes place by fission. They also have the power of regeneration.

So, the correct answer is ‘Platyhelminthes’.

Note: Platyhelminthes show advancement over Ctenophores by organ system level of organization, sense organ present in the anterior end of the head. Some flatworms are endoparasitic in humans which infect the liver and blood.