Eric's class was conducting a nudibranch survey recently, and thanks to Zoe's sharp eyes we were introduced to an interesting sea slug — meet Olive's Sapsucker (Hermaea oliviae)! This is the first time we've encountered this species.
It's easy to understand why this sea slug isn't seen that often. They're tiny — this one was only ~5 mm long. And they look a lot like the algae they eat — in this case, Polysiphonia (perhaps Polysiphonia hendryi).
Sacoglossan slugs look similar to nudibranchs, but note the rolled (rather than rounded) rhinophores (the sensory structures that look like tentacles in front of the eyes).
Here's the entire animal (below). It was fun to see them cruising around!
P.S. With many thanks to Zoe for spotting such a cool little slug!
P.P.S. Thanks to Jeff for assistance with this identification.
P.P.P.S. For an example of a different species of sap-sucking sea slug, see the post called "One cell at a time" on 23 September 2017.
You do a fantastic job of sharing such unique animals! What are the big dark things in the photo? There are about 20 of them, and they dominate the photo.
ReplyDeleteHello, and thanks for the question!
ReplyDeleteI think the dark structures you're looking at are the cerata -- these are upright finger-like projections on the sea slug's back. Cerata are important in a variety of ways -- they help with respiration and with defense. Sometimes cerata contain stinging cells that will deter predators, or sometimes the sea slug can drop some cerata and that will distract a predator.
Jackie
P.S. Some nudibranchs have cerata -- you can see another example in the opalescent nudibranch photo from 3 July 2022 -- while others don't.