Rhabdocoels

Rhabdocoels are a group of free-swimming or parasitic flatworms belonging to the class Trematoda, although their taxonomic placement has been subject to revision. They are characterized by the presence of rhabdites, which are rod-shaped structures embedded in the epidermis, that are discharged to form a protective mucus layer. These worms typically have a simple, unsegmented body plan with a distinct anterior and posterior end. A characteristic feature is their pharynx, which is often bulbous and muscular, and a branched gut that lacks an anus. Rhabdocoels exhibit a wide range of lifestyles. Many are free-living, inhabiting freshwater and marine environments where they feed on small invertebrates, algae, or organic detritus. Others are parasitic, with complex life cycles involving one or more intermediate hosts, often mollusks, to reach their definitive hosts, which can include fish, amphibians, and reptiles. Their small size and often cryptic nature make them a less commonly encountered group compared to other flatworms. Research into rhabdocoels continues to explore their evolutionary relationships, ecological roles, and the diverse adaptations that allow them to thrive in various habitats.