GENERAL HISTOLOGY

Detailed explanation-1: -Reproduction in echinoderms is typically by external fertilization; eggs and sperm are freely discharged into the water. A few sea urchins brood their eggs in special pouches, but most provide no parental care.

Detailed explanation-2: -External Fertilization The release of the reproductive material may be triggered by water temperature or the length of daylight. Nearly all fish spawn, as do crustaceans (such as crabs and shrimp), mollusks (such as oysters), squid, and echinoderms (such as sea urchins and sea cucumbers).

Detailed explanation-3: -External Fertilization After the sperm reaches the egg, fertilization can then take place. Most external fertilization happens during the process of spawning where one or several females release their eggs and the male(s) release sperm in the same area, at the same time.

Detailed explanation-4: -Echinoderms shows external fertilization, the eggs and sperm cells are released into open water, where fertilization takes place. Hence, option B is correct.

Detailed explanation-5: -Descriptive external fertilization examples are that of salmon, trout fish, and codfish. Both the female and male release their eggs and sperms respectively into the water where they diffuse and fertilize. In the list of external fertilization examples, aquatic animals such as mammals and sharks are exceptions.