Nudibranchs are a group of shell-less marine molluscs. They are also known as sea slugs. Nudibranchs are hermaphrodites, meaning that they have both male and female reproductive organs. However, they cannot self-fertilize. Instead, they must mate with another nudibranch.

Nudibranch mating typically begins with a courtship ritual. This ritual may involve the nudibranchs circling each other, touching each other with their tentacles, and exchanging chemicals. Once the nudibranchs are ready to mate, they will align their bodies side by side and insert their reproductive organs into each other.

Nudibranchs have external fertilization, meaning that the sperm and eggs are fertilized outside of their bodies. The male nudibranch will release a cloud of sperm into the water, and the female nudibranch will collect the sperm on her mantle. The female nudibranch will then lay her eggs on a hard surface, such as a rock or a shell. The eggs are usually fertilized as they are being laid.

Nudibranch eggs are typically enclosed in a jelly-like capsule. The number of eggs that a female nudibranch lays can vary depending on the species, but it can range from a few hundred to several thousand. The eggs hatch into larvae, which swim freely in the water. The larvae eventually settle on a hard surface and transform into adult nudibranchs.