Pteraeolidia semperi (Bergh, 1870)

This large nudibranch is found in a variety of subtidal habitats. We did not see it on any of our shallow (0-2m) reefs, but it was relatively common in the deeper sites, although usually only one or two specimens at a time. Color varies from brown to the blue shown below. It is a hydroid eater, and stores the consumed but undischarged hydroid nematocysts in the tips of its cerata, where they are used in the nudibranch's defense. While it doesn't seem to affect tougher human skin, like the palm of your hand, it can sting if it touches something more sensitive. I have been stung on the back of my hand. It's generally not a serious sting, but like the hydroid it can cause small welts and itching after the stinging sensation goes away.

The specimen below is on its prey, the stinging hydroid Pennaria disticha.

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Created 20 April 2009
Updated 14 December 2015

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