Consider the following statements: I. All nematodes are parasitic in nature II. Earthworms are nocturnal animals III. Annelids have no true coelom. IV. The alimentary canal of flatworms has only one opening. Which of these statements is/are correct?

Statement I is incorrect because nematodes include both parasitic and free-living species, such as the model organism Caenorhabditis elegans [t4, t8]. Statement II is correct; earthworms are nocturnal animals that are active at night and sensitive to light. Statement III is incorrect because annelids are true coelomates, possessing a fluid-filled body cavity lined with mesoderm [t7, t8]. Statement IV is correct; flatworms (Phylum Platyhelminthes) are acoelomates with an incomplete digestive system, meaning their alimentary canal (gastrovascular cavity) has only one opening that serves as both mouth and anus [t3, t8]. Therefore, only statements II and IV are accurate. While some sources incorrectly label annelids as pseudocoelomates [t1], established biological classification confirms they are coelomates [t7, t8], making statement III false.