GENERAL HISTOLOGY

Detailed explanation-1: -Echinoderms shows external fertilization, the eggs and sperm cells are released into open water, where fertilization takes place.

Detailed explanation-2: -External fertilization in animals usually occurs in water or in damp areas in a process called spawning. Moisture in the environment keeps the gametes from drying out. Moisture is also important so the eggs and sperm can move around freely, which lets them meet and fuse.

Detailed explanation-3: -Each starfish arm contains two gonads that release gametes through openings called gonoducts, located on the central disc between the arms. Fertilization is generally external but in a few species, internal fertilization takes place.