Why Nudibranchs Are Impressively Good at Existing

Approximately 100 million years ago, ancestral sea snails evolved to lose protective shells, triggering explosive evolutionary radiation producing 3,000+ known nudibranch species with scientists estimating thousands more await discovery.

All nudibranchs function as simultaneous hermaphrodites possessing both male and female reproductive organs, with genital openings located on their right body sides enabling any two individuals to successfully mate.

Aeolid nudibranchs—those with bushy finger-like cerata appendages—consume cnidarian prey like jellyfish and sea anemones, harvesting immature stinging cells (nematocysts) and storing them in specialized sacs at cerata tips for their own defensive use.

Nudibranch chemical defenses enabled ancestral shell loss 100 million years ago, with modern species employing either synthesized toxins or stolen prey defenses (kleptocnidae) to deter predators despite soft, exposed bodies.

Nudibranchs divide into two main anatomical types based on gill structure and placement: dorid nudibranchs with feathery circular gills on dorsal surfaces, and aeolid nudibranchs with respiratory cerata covering mantles.

Over 3,000 known nudibranch species inhabit global oceans with scientists estimating thousands more await discovery, ranging from 4-millimeter miniatures to 600-millimeter Spanish dancers, exhibiting jaw-dropping colors making them arguably the ocean’s most beautiful creatures.

Most nudibranchs function as slow but nimble crawlers across substrates, though some species evolved free-swimming capabilities including hooded nudibranchs resembling ghosts (reportedly smelling like watermelon) and Spanish dancers undulating dramatically to relocate when disturbed.