The correct answer is option 1. Explanation & Key Takeaways: • Phylum Platyhelminthes belongs to the kingdom Animalia. • The organisms are also known as flatworms. • These are acoelomates and they include many free-living and parasitic life forms. • Platyhelminthes have the following important characteristics: • They are triploblastic, acoelomate, and bilaterally symmetrical. • They may be free-living or parasites. • The body has a soft covering with or without cilia. • Their body is dorsoventrally flattened without any segments and appears like a leaf. • They are devoid of the anus and circulatory system but have a mouth. • They respire by simple diffusion through the body surface. • They have an organ level of organization. • They do not have a digestive tract. • The space between the body wall and organs is filled with connective tissue parenchyma which helps in transporting the food material. • They are hermaphrodites, i.e., both male and female organs are present in the same body. • They reproduce sexually by fusion of gametes and asexually by regeneration by fission and regeneration. Fertilization is internal. • The life cycle is complicated with one or more larval stages. • They possess the quality of regeneration. • The flame cells help in excretion and osmoregulation. • The nervous system comprises the brain and two longitudinal nerve cords arranged in a ladder-like fashion. • Hence option 1 is correct.