Agassiz’s Nudibranch

Family: Chromodorididae
Size: Up to 8 cm (3 in) | Common: 4 cm
Depth: 1 – 30m (3 – 100ft)

Distribution: Eastern Pacific (Gulf of California to Peru, including the Galapagos and Malpelo).

Identification: A stunning, highly photogenic sea slug with vibrant warning colors.

• Color & Pattern: The main body is dark blue, black, or deep brown, densely covered in small yellow or white spots.
• The Margin: The "skirt" (mantle edge) is incredibly distinct: it features a bright orange or red outer band, followed by a white inner band.
• Anatomy: Look for the sensory tentacles on its head (rhinophores) and the feathery gills on its back (branchial plume), which are usually dark blue or purple with bright orange/red tips.

Behavior: A slow-moving specialist with a toxic defense.

• Diet: Like many nudibranchs, they are highly specialized feeders. They graze almost exclusively on specific types of sponges found on the rocky reefs.
• Defense Mechanism: They don't need a shell because they absorb the toxic chemicals from the sponges they eat. Their brilliant neon colors act as a visual warning (aposematism) to let predators know they taste terrible and are poisonous.