Entozoa

Entozoa is an obsolete taxonomic term that historically referred to a group of parasitic animals that live inside the bodies of other organisms.^[1] It was originally used in older classifications to describe a diverse assortment of internal parasites, including parasitic worms (like tapeworms and roundworms) and some protozoans.^[2] However, the term Entozoa is only broadly descriptive and not based on evolutionary relationships, making it a convenient but scientifically invalid grouping. Coined by Swedish-German naturalist Karl Rudolfi in 1808,^[3] the term is considered obsolete and no longer used in modern taxonomy.

Advances in taxonomy and phylogenetics have replaced such groupings with more precise classifications based on evolutionary relationships.^[4] Today, these organisms are classified within different kingdoms or phyla, such as Protozoa (single-celled organisms, like Plasmodium, a cause of malaria); Nematoda (roundworms, including the genus Ascaris); and Platyhelminthes (flatworms, like tapeworms and flukes).^[5]

The term Entozoa was initially used at a broad taxonomic level, closer to the rank of a kingdom or a similarly overarching group in older biological classifications. It functioned as a general, non-systematic category for all internal parasites, reflecting the limited understanding of evolutionary relationships in the early 19th century.