Platyhelminth, also known as flatworm, refers to a phylum of invertebrate animals that includes various species with a flat, ribbon-like body shape. The word "platyhelminth" is derived from the Greek words "platys" meaning flat, and "helminthos" meaning worm.
These organisms belong to the animal kingdom and are characterized by the absence of a body cavity and a lack of specialized respiratory and circulatory systems. They possess bilateral symmetry, meaning their bodies can be divided into two equal halves along a central axis. Platyhelminths exhibit a dorsoventrally flattened structure, which allows them to adhere tightly to surfaces like rocks or host organisms.
Some well-known examples of platyhelminths include tapeworms, flukes, and planarians. While many species are parasitic, living inside or on the bodies of other organisms and obtaining nutrients from them, there are also free-living species that inhabit freshwater, marine, or terrestrial environments.
Platyhelminths have a relatively simple nervous system and lack complex organs, like a digestive system or respiratory system, which limits their overall physiological complexity. However, they do possess a ladder-like nervous system and specialized sensory structures to detect light, chemicals, touch, and temperature.
The lifecycle of platyhelminths usually involves sexual reproduction, although some species can also reproduce asexually by regenerating lost body parts. The phylum Platyhelminthes encompasses a wide range of species with diverse characteristics and adaptations, making them a fascinating group of invertebrates with important ecological roles.
