rotifer

Rotifers are a diverse group of microscopic aquatic animals in the phylum Rotifera. They are typically 50 to 1000 micrometers long and inhabit freshwater, marine environments, and damp terrestrial habitats such as soil and mosses. They play important roles in aquatic ecosystems as grazers of microalgae, bacteria, and detritus, and serve as prey for small invertebrates.

Anatomy and physiology: The anterior end features a corona, a wheel-like arrangement of cilia that creates water currents for feeding and locomotion. The mastax, a muscular jaw apparatus inside the pharynx, contains trophi of various shapes used to grind food. The digestive tract is complete, and a pseudocoelom provides a body cavity for organs. The nervous system includes a simple brain (cerebral ganglion) and longitudinal nerve cords. Excretion occurs via protonephridia with flame cells. Many rotifers have a protective lorica or shell, and some possess a retractable foot with toes for attachment to surfaces.

Reproduction and life cycles: Reproductive strategies vary. In many freshwater monogononts, females reproduce asexually by amictic parthenogenesis, producing diploid offspring without fertilization; under stressful conditions, they switch to producing resting eggs that can survive harsh periods. Bdelloid rotifers are famous for predominantly reproducing by parthenogenesis, with males rare or absent in many populations. Sexual reproduction occurs in some groups and typically results in resting or diapausing eggs that enhance survival.

Taxonomy and diversity: The phylum includes major groups such as Bdelloidea, Monogononta, and Seisonidea. Rotifers are closely related to Acanthocephala within the larger grouping Syndermata. They exhibit a wide range of morphologies, from free-swimming pelagic forms to sessile, life-supporting structures in various habitats.