Consider the following statements regarding different types of animals: 1. Cnidarians are acoelomate 2. All sponges (Porifera) are marineare marine 3. Flatworms (Platyhelminthes) can produce asexually 4. In arthropods, fertilisation is always internal. Which of these statements is/are correct?

Statement 1 is correct; Cnidarians are acoelomate as they lack a true body cavity (coelom) between the body wall and digestive tract, possessing only a jelly-like mesoglea [t10]. Statement 2 is incorrect; while most sponges are marine, the family Spongillidae consists of freshwater species [t1, t8, t10]. Statement 3 is correct; flatworms like Planaria exhibit asexual reproduction through fragmentation, regeneration, or transverse binary fission [c1, c4, t4, t6]. Statement 4 is incorrect; while many terrestrial arthropods (like insects) use internal fertilisation, many aquatic arthropods (like certain crustaceans and horseshoe crabs) exhibit external fertilisation where gametes are released into the water. Therefore, only statements 1 and 3 are correct, making option 2 the right choice.

Sources

1. [1] https://sist.sathyabama.ac.in/sist_coursematerial/uploads/SBC1201.pdf
2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 13: Our Home: Earth, a Unique Life Sustaining Planet > Ever heard of ... Ever heard of ... > p. 221
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 7: How do Organisms Reproduce? > 7.2.3 Regeneration > p. 116