platyhelminth

Platyhelminth is a phylum of invertebrate animals comprising the flatworms. This phylum is divided into two classes: Turbellaria, which are free-living flatworms, and Trematoda and Cestoda, which are parasitic flatworms. Platyhelminths are characterized by their flattened, unsegmented bodies, bilateral symmetry, and the absence of a coelom, or body cavity. They possess a digestive system that is typically incomplete, with a single opening serving as both mouth and anus. Respiration and excretion are generally carried out through diffusion across the body surface.

The nervous system of platyhelminths is relatively simple, consisting of a nerve net or a ladder-like system with a concentration of nerve tissue at the anterior end, forming a rudimentary brain. Many free-living species have simple eyespots that can detect light. Reproduction can be sexual or asexual. Many parasitic species have complex life cycles involving multiple hosts. Platyhelminths inhabit a wide range of environments, including marine, freshwater, and terrestrial habitats. They play important ecological roles, both as free-living predators and scavengers, and as parasites that can affect the health of their hosts.