Sea hare

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Wim van Egmond
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Joined: Tue Aug 15, 2006 9:28 am
Location: Berkel en Rodenrijs, the Netherlands

Sea hare

Post by Wim van Egmond »

The Sea hare is a large shell-less gastropod. They are easy to observe during low tide and during the mating season you may find many. The adults can be 30 centimeters or longer.

I have photographed them mating, and also photographed the eggs. they are tiny, the image width of the image below is about 5 centimeters. One individual lays almost half a billion eggs! When the eggs are collected in a jar you can wait for them to hatch.

In the Microforum there are some pictures of the larvae. These have shells!

best regards,




Bruce Williams
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Location: Northamptonshire, England

Post by Bruce Williams »

Very interesting post Wim. I've not come across the Sea Hare before - although for some reason the creature looks familiar?

These photos are excellent and your larvae pics in the microscope forum are not to be missed either.

Bruce :D

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Post by Planapo »

Yes, very welcomed addendum where the veliger larvae came from. And a very clean and well lit macro shot of the eggs, imho.

Betty :D

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Re: Sea hare

Post by rjlittlefield »

Wim van Egmond wrote:One individual lays almost half a billion eggs!
Not necessarily all at once, though.

In "The Egg-Laying Activities of the Sea Hare, Tethys californicus (Cooper)", pdf file here, it is written that:
Table I gives a summary
of the egg-laying activity of a sea hare weighing 5 pounds, 12 ounces,
which laid 478 million eggs between October 29, 1933 and March 6,
1934, inclusive, or within four months and one week.
After each laying (27 in all) the eggs were drained of surplus
moisture and then weighed. By measuring and weighing lengths of
string from several layings it was found that one gram of egg string
averaged 21.55 cm. in length. By multiplying the weight of the mass
laid by 21.55, the total length of the egg string was obtained. In the
27 layings the sea hare laid a total of 60,565 cm. of egg string, 17,520
cm. of which were laid in the first laying. Also after each laying ten
or more samples of the egg string were taken at different places through
out its length. From these samples the average number of capsules per
centimeter was counted, the average for the entire lot being thirty-nine.
The number of capsules per centimeter showed less variation than any
other factor, the number of eggs contained in a capsule having no effect
on its size. In fact, sometimes at the end of a laying several centimeters
of string would be laid which would contain no eggs, or perhaps only a
few, yet even in this portion of the string there would be about 39 cap
sules per centimeter. The number of eggs was counted from several
capsules in each of the representative samples and the average computed.
These averages are given in column three of Table I. The average
number of capsules per centimeter times the average number of eggs
per capsule gave the number of eggs per centimeter. By multiplying
the average number of eggs per centimeter in each laying by the length
in centimeters, the total number of eggs for that laying was obtained, as
given in column four of Table I.
I will spare you Table I, except to note that the largest individual laying was the first: 813 grams of eggs, with 217 eggs per capsule, totalling 148 million eggs (approximately 1/3 of the final total). :shock:

I gather from this description that each egg is one of the individual little pink dots that we can see in the second photo here. The clusters of pink dots must be the "capsules"?

This is a very interesting animal that had escaped my attention.

Wim, I don't suppose that you happen to have a closer view of the egg mass? <insert begging puppy emoticon> :D
In the Microforum there are some pictures of the larvae. These have shells!
I was intrigued that the larvae have shells while the adults apparently do not. At I found an explanation that "In most species of Sea Hare the shell is well enclosed within the mantle tissue, but in a few species like A. punctata and A. parvula there is a wide opening [mantle foramen] in the mantle tissue exposing quite a bit of the shell to the outside world. When these animals get old and worn out, this opening gets bigger and bigger as the mantle tissue loses 'muscle tone' and the shell becomes even more exposed." Exposing of the shell is illustrated in that post. Photos of other shells are shown at ... =aplyshell , as well as the comment that "In other genera...the shell is completely absent." Links in those articles, and the whole site, contain much interesting information!

Thanks for the posting, Wim -- you have made my day!


Wim van Egmond
Posts: 826
Joined: Tue Aug 15, 2006 9:28 am
Location: Berkel en Rodenrijs, the Netherlands

Post by Wim van Egmond »


That is very interesting!

I should have read a bit more about that organism. I did not realise it still had a shell.

That is a good method of counting the eggs. I started counting but I missed a 'loop' so I had to stop after 2 days. :)

The packages with eggs are not so big 10 centimeter in diameter so I knew they had to lay many such packages to reach that number. Still, it is an amazing number.

I will see if I can post an image with a close up.

best regards,


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Location: Copenhagen Denmark

Post by tpe »

Great post and great pictures there wim, thanks for posting.


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Post by beetleman »

It is always nice to see you on this side of the forums Wim. I know you always have something exciting and unusual to show us. This is a great example.
Take Nothing but Pictures--Leave Nothing but Footprints.
Doug Breda

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