Tag Archives: Nudibranch

Invertebrate Locomotion in the Ocean

At the Catalina Island Marine Institute, we are all about being active and on the move.  The same goes for the invertebrates in our labs! But how do they move? Magic? Super powers? Thinking happy thoughts? Actually, we can explain with…..science!

Some of the animals in our lab move by using their little tube feet.  These are animals like the sea stars, sea cucumbers, and urchins, which are all members of the phylum Echinodermata.  Echinodermata translates to “spiny skin”.  Not only do the members of this phylum have spines, they also have sticky little feet! In fact, if you look underneath any of these animals, you will see what looks like little tubes with suction cups on the ends.  The animal will extend these tube  feet in the direction it wants to go, suction on, and then pull itself along.  Sometimes the tube feet can also be used as levers and for food capture. The tube feet can also be used to help the animal stay in place, if say, kids—I mean… “seagulls”—..were trying to grab at them! So cool.

Some of the friends in our Mollusk tank, such as the California Sea Hare, Aplysia californica, and the Spanish Shawl nudibranch, Flabellina iodinea, move in a different way.  These animals have a soft slug-like body, the length of which is called a “foot”.  Weird, I know, imagine if your whole body was called a foot! So the foot produces slime and when the animal contracts its muscles and moves tiny hairs on its body through the slime it manages to scoot, scoot, scoot! 

As if this wasn’t enough, many of the slugs can also swim (Fig.2)  The Spanish Shawl and the Lion’s Mane, Melibe leonina, can swim by whipping their head back and forth towards the end of  their foot. It can be an effective way to respond to predators, and kind of looks like they are throwing down for a dance off.

The take away here is that there are many ways to move through life, and invertebrates are great role models for showing us how it’s done! There’s no right or wrong way, whether you have many sticky feet, a whole body called a foot to scoot around on slime with, or maybe you just whip back and forth—- no kind of motion is too “loco” to be in the ocean!





Have you ever been snorkeling and come across a brightly colored sea slug looking like creature? Well that means you may have just stumbled across a nudibranch!

It is estimated that there are over 3,000 species of nudibranchs making these “naked gilled” invertebrates the largest order of opisthobranchs, “sea slugs”, found in our ocean! And because there are such a varied amount of nudibranchs these incredible invertebrates can be classified under one of four suborders:

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  1. Doridina – Dorids make up the largest suborder of nudibranchs. They typically have a flat or tube shaped body as well as branchial plumes, or anal gills.
  1. Aeolidina – Aeolids make up the second largest suborder of nudibranchs. They have long tubular bodies as well as rows of respiratory organs referred to as cerata.
  1. Dendronotina – Dendronotids and Melibes have tubular bodies as well as gills in spindle or branched formations.
  1. Arminina – Arminids are more so the types of nudibranchs that do not fit into the other three suborders. They typically have gills on the side of their body and a velum, or oral veil, on their head.

Nudibranchs have very limited sight. Although they do posses eyespots, nudibranchs can only really detect light with their eyespots; they do not have the ability to see images or color. So unfortunately nudibranchs will never realize how stunning they truly are.

Nudibranchs also lack taste buds therefore they utilize a sense other than taste to find food. These awesome creatures possess rhinophores (“rhino” meaning nose and “phore” meaning carrier) in order to detect chemical molecules in the water and hunt down prey.

Nudibranchs are pretty intelligent creatures because they utilize products from algae and other animals in their day-to-day lives. For example some nudibranchs form symbiotic, mutually beneficial, relationships with chloroplasts and zooxanthellae. They store them in their bodies and then utilize the energy produced by chloroplasts and zooxanthellae either as a source of food or even an energy boost! Aeolids even have the ability to feed upon nematocysts (stinging cells), store them in cnidosacs at the tip of their cerata, and then use these nematocysts as a form of defense!

Written By: Alex Feltes


Behrens, David W. Nudibranch Behavior. Jacksonville, FL: New World, 2007

Behrens, David W. Pacific Coast Nudibranchs. Monterey, CA: Sea Challengers, 1991


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