Nudibranchs on Vashon

Nudibranchs (which is pronounced nudibranks) are the most amazing, complex and beautiful creatures of the sea.

I thought that I would draw a cartoon for this article, since nudibranchs are really hard to describe…but I thought that might not be such a great idea since the Loop is printed in black and white and I didn’t have a lot of confidence in being able to render a nudibranch without using color. Plus, there is just so much information to impart that I don’t think I’d be able to convey all the amazing aspects of nudibranchs with illustration alone.

Color! That is what drew me to nudibranchs in the first place (well that and some of the crazy forms they take). It is as if they are constantly being lit by a black light…they are decorated in pigments that were only just invented in the 20th century. But I’m getting ahead of myself.

For those who don’t remember any of their biology from high school and beyond, here are the basics: Nudibranchs belong to the family or Phylum Mollusca, the class Gastropoda, subclass of Opisthobranchia…it is the order of Nudibranchia of which there are 4 suborders including:

Doridina, Dendronotina, Arminina and Aeolidina….whew!

Okay take a breath…I don’t like all the very difficult biological references but I must continue because it is essential to understand these animals. They are commonly called "Sea Slugs", but don’t resemble any of the terrestrial prosobranchs that we have here, nor do they eat our gardens. Prosobranchia is a large taxonomic subclass of sea snails, land snails and freshwater snails. Nudibranchs are related to all those sea snails and clams that we think of when we hear the word mollusks, and like their cousins squid and octopus, they evolved "towards the reduction, internalization and complete loss of the shell". While some appear to be slug-like, some are translucent with frills and others are more opaque and dense in appearance – sometimes appearing to be half a lemon sucked onto a rock in the sea.

There is a ton of diversity in these creatures - shape, color, size, habits and sex, and yet they share many common traits. Every part of their beings has a purpose. Remember the psychedelic colors that I was first drawn to? Their colors are a self-defense evolution. We are talking about shell-less creatures with no outwardly observable defenses, except that their color tells other (but not all) predators that they taste bad and shouldn’t be eaten. Fish have been observed taking nudibranchs into their mouths and then spitting them out, duh, they taste bad! These creatures are pretty extroverted, crawling over and under rocks, sliding atop sand or like some, swimming along. They are confident in their unpalatable taste. Their coloration can also help them "blend" into the background, occasionally mimicking other creatures (such as hydroids). But color isn’t their only self-defense strategy…they can also emit secretions of toxic chemicals like sulfuric acid (probably why they also taste so bad) or by firing stinging cells (nematocysts that they have stolen from other animals like anemones).

Feeding: Most nudibranchs possess a drill-like ribbon of teeth in their mouths called the radula which have been adapted to the animal’s particular prey. Dorid nudibranchs, for instance, don’t have very strong "jaws". They graze upon encrusting marine sponges and barnacles (that feed in turn on encrusting bryozoans, so I guess they taste like what they eat). The size, shape and number of teeth have been specifically evolved for that dinner. Aeolid and a few dendronotid nudibranchs feed on hydroids and stalked bryozoans and have narrow radulae and well developed jaws (maybe I should have made a cartoon). Now I should also emphasize the fact that each species can have their own variations of radula and jaws depending on who they are and where they live: diversity, diversity, DIVERSITY!

Nudibranchs are equipped with sensory organs that are located around their gills which enable them to sense chemical changes in their environment. There are rhinophores at their head ends, which are believed to work like a nose/tongue…sometimes looking like rabbit’s ears. It is thought that a nudibranch’s rhinophores help them sense food and possibly a mate. These can be retracted into the body when necessary to protect them from being eaten. Nudibranchs have primitive eyes embedded deep in their bodies. They can’t see images per se, but can see light and dark.

Then there is sex. Nudibranchs defy our logic of separate sexes. Although most prosobranch snails have separate sexes, virtually all opisthobranchs (nudibranchs) are hermaphroditic. Each individual possesses both male and female sex organs. Eggs and sperm often develop in an individual’s body at the same time. In-going and outgoing sperm and eggs even use a common aperture. Some start out life with male organs and as they age gradually become female. However they are incapable of self-fertilization.

There is great variety in the development, shape, coloration and size of the eggs of the different species. Dorid egg masses are shaped like a ribbon while aeolids and dendronotids lay egg strings. As with humans, the younger the nudibranch, the more eggs get laid and as they age fewer and fewer eggs are laid. Eggs are usually laid on or underneath rocks or algae.

To find nudibranchs in the wild, go out on a low tide and chances are that with a careful eye to the ground, you will see one. I usually find them under rocks in the pools of water underneath. I have seen Armina Californicas out on sandy beaches of the west side of the island. Nudibranchs range in size between ½ inch and 3 inches depending on the species.

I hope this inspires you to go to our beaches. Remember – low tides! Come to the Pt. Robinson Low Tide Celebration on July 4 from 10am to 3pm to ask a beach naturalist for help finding a nudibranch. For pictures and more information, search online for "pacific northwest nudibranchs" and you’ll see lots of amazing pictures!