“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 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 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.
The Marine Detective 
5 Responses to ““Exquisite Handiwork” – Sea Slug Eggs”
I’m always amazed at your blogs; the caring, the wonder, and the time you put into it. Such great work Jackie!!! Thank you.
Thank you Ang! To know you are part of the audience is a further motivator!
they really are like little doilies aren’t they? I had no idea. If they are hermaphrodite then why are they mating? (that sounds sarcastic and isn’t meant to be) How many eggs are in each cluster approximately? And do they lay more than one each season? I wondered how many actually survive to become adult.
sorry for the many questions but they really pique my interest.
thanks
ev
Thrilled to peak your interest and will address all questions a little later. Nature still favours genes mixing. Hermaphrodites don’t inseminate themselves. They can inseminate and be fertilized. Massive hug to you Ev. So appreciate the interest!
Hello again Ev, Having done a quick count on a segment of a close-up of the eggs and then using this to form an estimate, I would say that the egg mass has about 35,000 eggs. Also of interest may be that they are called “sea lemons” as apparently they give off a mild, lemon-like scent.