Rhabdocoela

Rhabdocoela is an order of microscopic, free-swimming or crawling flatworms belonging to the class Turbellaria. These flatworms are characterized by the presence of rhabdites, which are rod-shaped structures embedded in the epidermis. When discharged, rhabdites swell and absorb water, forming a protective mucous sheath around the worm, or aiding in locomotion and prey capture.

The body plan of rhabdocoels is typically unsegmented and dorsoventrally flattened. They possess a simple digestive system, usually with a pharynx that can be extended to ingest food. Their nervous system is primitive, consisting of a nerve net and a pair of anterior ganglia. Most rhabdocoels are hermaphroditic, reproducing both sexually and asexually.

Rhabdocoels inhabit a wide range of aquatic environments, including freshwater, marine, and brackish waters. They can be found in various microhabitats such as sediments, plant surfaces, and even within the bodies of other invertebrates as commensals or parasites. Their diet consists primarily of small invertebrates, algae, and organic detritus. Some species are predatory, while others are detritivores.

The order Rhabdocoela is a diverse group with numerous families and genera. Their ecological roles vary depending on the species and habitat, contributing to nutrient cycling and serving as a food source for larger organisms. Research on rhabdocoels often focuses on their unique biology, evolutionary relationships, and ecological interactions.