Which one of the following statements is not correct ?

Option 1 is incorrect. Echinoderms are mostly dioecious and typically undergo external fertilization, with eggs hatching into planktonic, free‑swimming larvae rather than developing viviparously; thus they are not all viviparous [1]. Roundworms (nematodes) lack a true circulatory system, so statement 2 is correct. Most bony fishes (Osteichthyes) characteristically possess a swim bladder used for buoyancy regulation, so statement 3 is correct [2]. Cartilaginous fishes (sharks, rays) commonly exhibit internal fertilization, making statement 4 correct. Therefore the only statement that is not correct is (1).

Sources

1. [1] https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Introductory_Biology_(CK-12)/11%3A_Invertebrates/11.12%3A_Echinoderms
2. [2] https://www.sciencedirect.com/topics/immunology-and-microbiology/protostomia