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Updated 2/27/2024



Families are grouped below by form rather than taxonomic order.  Includes slug-like mollusks not belonging to Class Opisthobranchia.


Hawaii has many types of opisthobranchs, better known as sea slugs, some of which are undescribed species.  Many species experience population surges, abundant some years and absent others, or seasonal surges.  Most live less than a year and will be found near the specific food they eat including seaweed and a wide assortment of small invertebrates such as sponge, cnidarians, and mollusks.  Slugs that feed upon green seaweed store ingested chloroplast cells with in their mantle for photosynthesis.  Sea Hares produce a purple ink from red algae when disturbed.  Others may produce toxic compounds from food or store stinging cells in the body as defense against predators.  Animals with somewhat transparent flesh will assume the color of their prey.  Opisthobranchs are found under stones, on shaded walls, or within caverns.  The pelagic Glaucus atlanticus floats on the sea surface.  As with many invertebrates more may be seen at night.

Pittman & Fiene's Sea Slugs of Hawaii website

Sea slug eggs

Ft. Kamehameha, Oahu, 3 feet



Sharks Cove, Oahu, 25 feet


Sharkfin, Lana'i, 20 feet

Blowhole, Oahu, 35 feet

YO-257 Wreck, Waikiki, Oahu, 75 feet