Sea Slugs / Nudibranchs | The Marine Detective

Posts from the ‘Sea Slugs / Nudibranchs’ category

Big Orange Love – The Orange Peel Nudibranch

Update November 2020: The Orange Peel Nudibranch has been reclassified to now be Tochuina gigantea. See source below.

Here’s a Valentine’s related blog item. It’s all about Big Orange Love – the reproduction of the Orange Peel Nudibranch (Tochuina gigantea).

Orange Peel Nudibranch feeding on Red Soft Coral. Photo: Hildering

These sea slugs are very aptly named since their skin is reminiscent of both the texture and vibrant colour of an orange. But, the name does nothing to indicate the size to which these giants can grow. They are one of the world’s largest sea slugs with literature reporting them to lengths of up to 30 cm. However, I swear I have seen them larger in our area.

As if this sea slug species’ colour, size and beautifully intricate white gills are not enough to create awe, you should see their eggs! I will never forget the first time I saw the huge tubular mass that looked like udon noodles. I think my brain almost exploded and I was propelled all the more feverishly on my “The Marine Detective” path, wanting to be able to identify the egg masses of all sea slugs in our waters (each species’ eggs look different).

This is the time of year when the Orange Peel Nudibranchs mate and lay eggs.

It’s all to be seen on my “Big Orange Love” slideshow below.

Orange Peel Nudibranch beside egg mass. ©Jackie Hildering.

Close-up on an Orange Peel Nudibranch egg mass. Every little dot is an egg. ©Jackie Hildering.

©Jackie Hildering.

Sources:

Korshunova T, Martynov A (2020) Consolidated data on the phylogeny and evolution of the family Tritoniidae (Gastropoda: Nudibranchia) contribute to genera reassessment and clarify the taxonomic status of the neuroscience models Tritonia and Tochuina. PLoS ONE 15(11): e0242103. https://doi.org/10.1371/journal.pone.0242103

They’re Back . . . Hooded Nudibranchs

In late August, some of my Young Naturalists alerted me that they had already seen hooded nudibranchs (Melibe leonina) around Port Hardy (B.C., CANADA).

[It so wonderful that these local children know and greatly appreciate nudibranchs.]

Late August is earlier than we historically have seen the hooded sea slugs gather in large numbers. Usually this happens in late September / early October with them beginning to lay eggs in the spring.

Hooded nudibranchs back in very large numbers. Late August 2010.

This week, I had the opportunity to check how many are already in the area and, it’s official – the hooded nudibranchs are very much back.

To see the video from today, click here (2-minute video).

For explanations on the natural history of hooded nudibranchs, please see my previous blog postings from April 10th, 2010 and May 2nd, 2010.

Hooded nudibranch egg masses (March 2011). Each mass is about 1 cm high. Each little white dot is an egg.

Hooded nudibranch egg masses (March 2011).

“Exquisite Handiwork” – Sea Slug Eggs

“Some of nature’s most exquisite handiwork is on a miniature scale, as anyone knows who has applied a magnifying glass to a snowflake.“

I was reminded of this Rachel Carson quote today when diving but found myself changing the ending to ” . . . as anyone knows who has seen sea slug egg masses.”

The image here is the egg mass of the Pacific Sea Lemon (Peltodoris nobilis), a sea slug up to 20+ cm. It’s egg mass is up to some 20 cm as well. Every little dot you see contains up to 20 fertilized eggs. So many eggs are needed when your young are hatched into the planktonic soup of the sea.

The egg mass is the result of the Sea Lemons lining up right-side-to-right-side and both becoming fertilized. Being a hermaphrodite is of course a good design when you are a slow-moving slug that relies on smell to find its way. More detailed information about sea slug mating can be found at t his previous TMD blog entr y.

Looking like rich, textured crocheting, the egg mass is indeed Nature’s exquisite handiwork. Its intricacy rivals that of any spider’s web and, in my perception, surpasses any human nanotechnology.

Seeing such beauty serves as testimony of Nature’s perfection and complexity. How we humans are newcomers to it all, unable to truly grasp the billions of years of design that proceeded our walking upright on earth. It should further motivate us all to walk with much smaller footprints so that we do not blunder and crush the systems that are Nature’s exquisite handiwork.

Note: The Sea Lemon is often mistaken for other dorid species such as the Monterey Dorid (Doris montereyensis). The easiest way to ID them correctly is to know that Pacific Sea Lemons have white gills. See the photos below and note how, although the body colour can be different, the colour of the gills is always white. The gills of the Monterey Dorid are yellow. The other difference, albeit more subtle, is that the little brown bits of colour do not extend to the top of the tubercles in Pacific Sea Lemons and the brown does go to the tips in Monterey Dorids. The tubercles are those bumpy little structures all over the sea slugs. Also, every sea slug species’ egg masses looks different which provides further ID clues. The egg masses of Monterey Dorids are not quite as intricate.

[Update 2020: I promise I will provide a blog showing the differences in IDs and egg masses of Pacific Sea Lemons, Monterey Dorids AND two more species which add to the ID confusion – Freckled Sea Lemons and Heath’s Dorids. Just need a bit of time!]

Close up on a Pacific Sea Lemon’s (Peltodoris nobilis) egg mass. Every dot contains up to 20 fertilized eggs.

Peltodoris nobilis egg laying (note the Brittle Star arms coming out of the crack).

Peltodoris nobilis mating – always right side to right side in slugs with gonopores linked so both become inseminated and lay eggs = simultaneous hermaphrodites.

The following photos give more of a sense of the variation in colour in this species.

More mating and eggs masses

3 Pacific Sea Lemons, two mating, one egg mass. Individuals appear to lay multiple egg masses to increase the chances of young surviving to adulthood. Not the white gills.

Mating. These two were right beside the egg mass in the following photo.

Hooded mystery #2 – Hooded nudibranch swimming

See last week’s post for Part 1 about Hooded Nudibranchs (Melibe leonina).

This week, I share video showing this remarkable sea slug when it is swimming.

When viewing the clip, try to identify the animal’s “rhinophores”, the structures coming off the animal’s head that allow it to smell its way around. These structures have the shape of mouse ears but they pick up on chemical signals, not sound. In last week’s posting I shared how the Hooded Nudibranchs come together to mate through being attracted by smell (pheromones).

Video from today of a swimming Hooded Nudibranch.

The lobed structures on the animal’s back are the naked (nudi) gills (branchs). They can detach if the hooded nudibranch is threatened and are sticky. Maybe this is so that the predator is distracted by the gills sticking to it allowing the hooded nudibranch to have a greater chance of getting away.

Hooded Nudibranchs (up to 17.5 cm) on Giant Kelp.

I have included a second clip this week too, taken on today’s dive. No Hooded Nudibranchs in it, but Bull Kelp forest visions while on my “safety stop”; a 3-minute rest at 15 feet to offload nitrogen before surfacing. Thought you might like to take a dip with me!

Click here for kelp forest video from today’s dive.

Hooded Mystery – Hooded Nudibranchs and their eggs

Hooded Nudibranch – oral hood open to catch plankton. ©Jackie Hildering

The remarkable looking animals to the right are Hooded Nudibranchs (Melibe leonina up to 17.5 cm). A nudibranch is a type of sea slug that has naked (“nudi”) gills (“branchs”).

Starting in the fall, around NE Vancouver Island, they come together in order to mate and it is awe-inspiring to see 100s of them clustered together, delicate and ghost-like, clinging to kelp.

Often, you can see them swimming on the surface and many people mistake them for jellyfish. It is indeed one of the most alien looking of the 200+ sea slug species of our area. The large disc-like head lets it feed on plankton and small crustaceans and the lobed structures on the animals’ backs are the naked gills.

Hooded nudibranch swimming. ©Jackie Hildering

Since sea slugs can only sense light and dark, the way Hooded Nudibranchs signal one another is by emitting a fruity scent (pheromone) that attracts others of their kind. My personal experience after having picked up a dead Hooded Nudibranch on the beach, is that the smell is something like a mix of watermelon and grapefruit and the scent stayed on my hand for more than an hour.

After mating, both animals lay eggs (they are hermaphrodites) and then, they die. You can find additional information about why sea slugs are hermaphrodites at this past blog posting.

Hooded Nudibranch eggs. ©Jackie Hildering

Typically in our area they lay their egg masses between January and April. Each ribbon of eggs is only about one centimetre wide and contains thousands of eggs.

Every dot is an egg capsule contains 15 to 25 eggs. After about 10 days, depending on temperature, the eggs will hatch into larvae that will be part of the zooplankton soup of the Ocean. The larva are called “veligers” and look very different from the adult Hooded Nudibranchs.

They have a shell and a big flap on their head with which they swim and feed on smaller plankton. After 1 to 2 months, they settle to the ocean bottom and change body shape and even digestive tract to become small Hooded Nudibranchs.

A few of my video clips of this species below.

Unusually coloured Lions Mane Jelly near kelp draped in Hooded Nudibranchs. ©Jackie Hildering

Unusually coloured Lions Mane Jelly near Giant Kelp draped in Hooded Nudibranchs. ©Jackie Hildering

Hooded Nudibranchs on a rotting piece of Bull Kelp. ©Jackie Hildering

Sea Slug Easter Eggs For You!

Giant nudibranch's eggs laid at the base of its food, the tube-dwelling anemone. Each dot is an egg. © Jackie Hildering

To follow up on last week’s posting about the feeding of giant nudibranchs, “Who’s eating who”, I now share images of the giant nudibranch swimming and of its egg-laying behaviour.

I know that these are the strangest eggs you will see this Easter!

The story of how the eggs come to be is pretty unique too.

There are no girl or boy sea slugs. They are both male and female; they are hermaphrodites. This means that when sea slugs mate, both animals “get pregnant” and lay eggs.

Sea slugs need this adaptation because it is really difficult for them to find another of their kind. They are relatively slow moving animals that depend on feel and smell to get around.

They don’t search around aimlessly for a mate though. That would be a waste of energy. The chances of finding a member of their own kind are greater near their favourite food. To make this clearer, imagine that you were someone who really loved eating pizza and you wanted to find someone else who loved pizza. The best place to find them would be at . . . a pizza parlour!

For the giant nudibranch, you know from last week’s posting that they love to eat tube-dwelling anemones so they are likelier to meet a mate around this prey. They also may give off chemical signals (pheromones) to announce that they are in the area and “looking for love”.

Compared to faster animals that can see though, the chances of sea slugs finding one another are much smaller. So when they do meet, it is important that they really make it count and have as many babies as possible especially since the eggs will hatch into plankton. This means that many baby sea slugs will become dinner for filter feeders like anemones and barnacles.

How to have as many babies as possible? Both should lay eggs! This is why they are hermaphrodites; not just a male or female. The sea slugs line up right side to right side and exchange cells so that they can both lay eggs.

I will share much more about the love life of sea slugs in future postings. Every sea slug species lays eggs that look very different. One of the “cases” I have worked on the longest is to figure out what each species’ eggs look like. A great clue in trying to figure this out is that sea slugs most often lay eggs on their food.

You can imagine my delight when I found a big mass of eggs at the base of a tube-dwelling anemone! Knowing that the giant nudibranch preys on this species, the chances were very, very good that these were its eggs.

When you follow the link, you can see a larger picture of the eggs mass and get an idea of just how many eggs are in this string (each dot is an egg).

I have also included video of the giant nudibranch swimming for your Easter weekend pleasure. You’ll see that the nudibranch swims upwards but, when it wants to go down, it just stops moving and gently drifts back down to the ocean bottom. You’ll also see that I am pointing my dive light at the animal and how this makes colours look different underwater.

Who’s Eating Who?

Giant Nudibranch (Dendronotus iris) on the prowl for tube-dwelling anemones. This species of nudibranch has great variation in colour. © Jackie Hildering

Giant Nudibranch on the prowl for Tube-Dwelling Anemones. This species of nudibranch has great variation in colour. See photos at end of blog. ©Jackie Hildering

This “case” features the Giant Nudibranch (Dendronotus iris to 30 cm long) and the Tube-Dwelling Anemone (Pachycerianthus fimbriatus).

The Giant Nudibranch’s favourite snack is this anemone species. It is not impacted by the anemone’s stinging cells (nematocysts).

Giant nudibranch launching into a tube-dwelling anemone. © Jackie Hildering

The Tube-Dwelling Anemone is therefore adapted to be able to withdraw into its tube in an attempt to get away from the predator sea slug.

And the battle is on! The Giant Nudibranch patrols the sandy ocean plains “looking” for the Tube-Dwelling Anemone. When it finds one, it rears up and pounces, mouth parts extended in the hopes of grabbing onto the anemone. When the anemone senses the nudibranch’s attack, it withdraws into its tube.

Wait till you see what happens to the Giant Nudibranch!

See below for a short clip of such an attack.

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But that’s not all, this nudibranch species also swims.

By lifting off, it may land somewhere with better chances for feeding and mating. See video below.

As is also generally the way with sea slugs, they also lay their eggs on their prey.

And oh the diversity in colour among Giant Nudibranchs. See photos below.

Interspecies interaction: When this Giant Nudibranch touched the Leather Star, it touched it again and then recoiling with an acute change in direction. The diet of Leather Stars (Dermasterias imbricata) is omnivorous. From Neil McDaniel: “Eats a wide variety of prey, depending on the locale. On the open coast it consumes plumose anemones and tunicates; in sheltered areas it eats orange sea pens, sea vase tunicates, encrusting sponges and bryozoans.” So, Leather Stars are not likely to eat a Giant Nudibranch, especially because Leather Stars are not particularly fast sea stars (15 cm/min) and Giant Nudibranchs can swim away (yes, that’s right they swim). Leather Stars’ skin is known to contain a unique chemical “imbricatine” that does elicit an escape response form Swimming Anemones so . . . whether the Leather Star felt or “tasted” odd to the Giant Anemone, it did “decide” that distancing was the better way to go.

Correction from previous version of this blog: Dendonotids are not known to utilize the stinging cells (nematocysts) of their prey. From the Sea Slug Forum “There has been some confusion in the literature concerning the presence of branches of the gut in the ‘gills’ or ‘cerata’ of species of Dendronotus. Firstly there is no evidence to suggest that any species of Dendronotus has cnidosacs at the tip of its dorsal processes in which to store nematocysts. In fact there is no evidence that they store nematocysts from their prey anemones in any part of their body.“