Join me in the cold, dark, life-sustaining NE Pacific Ocean to discover the great beauty, mystery and fragility hidden there.

Posts tagged ‘sea slug mating’

Slugs that Fly? The Great Winged Sea Slug.

Here’s a species that deserves the descriptor “Great” without doubt – the GREAT Winged Sea Slug.

I will never forget the first time I saw one of these tiny sea slugs “flying” underwater.  My brain came close to exploding. I did not know of their existence prior to one flapping past my mask.

Dive buddy Natasha Dickinson pointing at a Great Winged Sea Slug.

 

Gastropteron pacificum is usually no bigger than your thumbnail. Maximum length is ~2 cm long and with “wingspan” to 4 cm. The species is also referenced as the Pacific Wingfoot Snail and the Pacific Batwing Sea Slug. But, as mentioned, I prefer the reference to their greatness.

Just marvel at how they can propel themselves, as captured in this video.

 

I will ALSO never forget the first time I saw them spawning, so many of them on the sandy ocean floor, their egg masses expanding to be bigger than they are.

I try to document this every year, looking in areas with sand in from late March into May. I have found them, and their eggs, as shallow as 2m depth.

And sure enough, on March 31st, there they were again. They are gathering to mate!

March 31, 2020 – “Beach Camp” near Port McNeill at only about 3m depth.

 

The photos below show you what the peak of the spawn looks like. Photos are from May 26th, 2019. Just look at the number of them! How do they find one another? How many eggs in an egg mass? So many questions!

 

I bet you also want to know how it can be that their masses of fertilized eggs are bigger than the sea slugs themselves. I presume the masses must expand with seawater but  .  . .  I do not know.

As is the case for most terrestrial and sea slugs, Great Winged Sea Slugs are simultaneous hermaphrodites whereby both parents become inseminated and lay eggs. It’s a great strategy to maximize chances of reproductive success when finding a mate is particularly challenging and your babies hatch into the planktonic soup of the ocean.

 

Among my many wonderings about this species is: Why have I never seen Great Winged Sea Slugs swimming during the time they are aggregating to mate?  I learned from research by Claudia Mills in Friday Harbour (published in 1994), that only sexually mature animals swim AND that they were only observed doing so between September and February i.e. not while mating.

Why swim? In may work well to escape annoying divers and/or bottom feeding fish like Ratfish. The timing suggests that it allows for population dispersal – spreading out for food and/or mates. You would think that the fact that hatch as plankton would spread them out enough. Also, HOW do they then assemble in numbers like this? Is it possible that these sea slugs smell one another’s scent trails even in the ocean?

You can see faint trails here.

 

Please know that this species IS a sea slug but it is NOT a nudibranch. Great Winged Sea Slugs don’t have naked gills and adults do have an internal shell when adults. Great Winged Sea Slugs belong to the group of sea slugs known as “bubble shells” of the order “Cephalaspidea”. You can even see the bubble shell in some of these images.  Ronald Shimek creatively described these sea slugs as having “an internal shell that looks quite like a soap bubble and is about as durable.”

The wing-like structures are called parapodia. When the sea slug is not swimming, these “wings” wrap around the body forming a water-filled cavity. See what looks like a siphon? Part of the “head-shied” folds into a siphon directing water into the cavity. There’s also an exhalant siphon.

The photo above is from the first time I ever noted this species. I was able to follow one as it drifted to the bottom and then saw the siphon appear. This added to the sensation that my brain was going to explode with awe. I shared the photos with experts and learned that, at that time (2007) it was not known what any members of the family feed upon. This added to my appreciation / understanding of how little is known about marine species that are even common and in the shallows. Bill Rudman responded with “I suspect they may feed on small flatworms or other invertebrate with no hard parts – but that is just a guess.” Apparently Gastopteron are known to feed on detritus and diatoms but it a laboratory setting, To my knowledge, there has not been confirmation of the diet of the species when in the wild.

I hope, dear reader, that these words and images offer an additional chance to get lost in the natural world for a little bit. It offers me such comfort to see the steady flow of the natural world around me – from the courting of song birds, to the emergence of plants, and the mating of sea slugs.

Know that, right below the surface, there’s a world or greatness  .  .  . where slugs fly.

 


Note that if you see similar egg masses in the intertidal zone,I believe they are more likely to be from one of two other sea slug species that are also “bubble shell” sea slugs (order Cephalaspidea).

#1) Diomedes’ Aglaja (Melanochlamys diomedea to 1.5 cm long ): A fabulously wicked little sea slug that crawls under the sand looking for other sea slugs to snack on.

Diomedes’ Aglaja crawling through the sand in the shallows.

 

The black blob under the sand is a Diomedes’ Aglaja.Believe the blobs are this species egg masses.

#2) Spotted Aglaja (Aglaja ocelligera to 3 cm long): Usually also under the sand and prey to Diomedes’ Aglaja.

A rare good look at a Spotted Aglajid since they are usually burrowed in sand. Notice how one tail is longer than the other.

 

Two Spotted Aglajids above the sand, presumed one is following the other’s scent trail to get together to mate.

 

A Spotted Aglajid laying eggs! “Aglajids lay their eggs in the most interesting way. They release the egg stream around their rotating body, creating a coil or tube-like mass. They then dive into the sediment placing an anchor so the eggs, above, won’t wash away.” Source: Dave Behrens.


Sources:

 

For an additional blog about another bubble shell sea slug in the NE Pacific Ocean see – “Shelled Sea Slug! A small mystery solved.”


Classification of Sea Slugs 

My attempt at summarizing the cassification of the group to which sea slugs belong.
Last updated 2020-04-17. Source: World Register of Marine Species.

Regarding the photo below:
The Opalescent Nudibranch is a nudibranch.  Nudibranchs DO have external gills (hence “nudi” = naked and “branch” = gills). Adults do NOT have an internal shell.
The Great Winged Sea Slug is a “bubble shell” sea slug (Cephalaspidea). They do NOT have naked gills and adults DO have an internal shell.
There! Now don’t you feel better knowing that: (1) Not all sea slugs have naked gills and hence not all sea slugs are nudibranchs; (2) However, all nudibranchs are sea slugs.

Big Orange Love – The Orange Peel Nudibranch

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

Sea slug amidst red soft coral.

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.

 

 

“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.

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 this previous TMD blog entry.

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 mass of Monterey Dorids is not quite as intricate. 

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. 

Close up on a Pacific Sea Lemon’s (Peltodoris nobilis) egg mass. Every dot is an egg.

 

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 the species.

 


 

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

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.