Nudibranch Life Cycle
Nudibranchs are gastropod mollusks, specifically types of sea slugs (close relatives of snails and terrestrial slugs) that derive their name, which means "naked gill," from the fact that they have lost their shell and their gills lie exposed on their dorsal surface. Before assuming their adult, slug-like shape, they undergo a series of transformations that take them from one larval stage to another before they become juveniles.
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Mating
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Nudibranchs are simultaneous hermaphrodites, because they possess functional male and female reproductive systems at the same time. As with all other gastropods, they only possess one gonad that in their case is called the ovotestis because it functions both as the male and female organ. Although this hermaphroditism can potentially lead to self-fertilization, this is very rare. Under normal circumstances two individuals exchange sperm, each one fertilizing the other's eggs.
Eggs
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Once fertilized, the eggs are laid in masses that can take various shapes and colors depending on the species of nudibranch. They are laid in close proximity to a source of food for the larvae that will emerge from the eggs. In many species the egg masses contain chemical compounds that are distasteful and protect them from predators.
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Trochophore Larva
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The trochophore larval stage is characterized by an overall round shape and a series of hairlike structures that have sensory and defensive functions. In nudibranchs this larval stage is greatly shortened and takes place entirely within the egg, before hatching.
Veliger Larva
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The veliger larval stage follows the trochophore stage, and it is at this stage that the young nudibranchs hatch. The veliger larva is unique to certain types of mollusks, among them nudibranchs. It is characterized by a structure called the velum that consists of two large lobes with long hairlike structures called cilia on the fringe. The veliger larva uses these cilia for swimming and feeding. The veliger larva differs from the juvenile and adult in that it is planktonic, meaning that it lives in the water column above the ocean floor.
Juvenile
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Eventually the veliger larva abandons the water column and goes to the bottom, becoming benthic. Here it undergoes metamorphosis and becomes a juvenile. Juveniles are individuals that resemble the adults in all respects except size and sexual maturity. From this point on the nudibranch will grow without further dramatic form changes. As an adult, it will reach sexual maturity.
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