The vast number of marine invertebrates are osmoconformers. B. Brackishwater Invertebrates Animals that penetrate into brackishwater may still be osmoconformers as long as they can tolerate the loss of salts and gain of water. However, most invertebrates that enter brackishwater exhibit some form of osmoregulation. All FW animals must osmo and ionoregulate, because it is impossible for a living organism to be isosmotic with such a dilute medium. However, most of these animals are fairly stenohaline, as they can t tolerate very high salt concentrations of the medium.
Lampreys do exhibit Osmoregulation - they are anadromous fishes for the most part.
B. Chondrichthyes Three main orders - sharks and sawfishes, rays, and chimeras. They normally maintain a slight hyperosmoticity with the environment. None of these animals live in FW - they simply migrate into FW for usually short periods of time. Thus, they act just like a bony fish. C. Osteichthyes 1.