This blog is so overdue. Over a year ago, a social media post I made about moonsnails went viral. That’s how many people valued learning that these egg collars are NOT garbage.
Below, I provide the image and text from that viral post but . . . this blog grew into so much more. Read on, I truly believe you will be moved by the marvel of moonsnails.
Text provided with the above image: “Oh oh. With recent low tides it has surfaced again that (mostly) well-intentioned people are moving or “cleaning up” moonsnail egg collars. These are not garbage. They are wondrous constructions to house and protectmoonsnail embryos (of several moonsnail species on our coast).
Detail: The female moonsnail forms one layer of the collar by gluing together sand grains with mucus; then the fertilized eggs are laid on this layer and THEN she seals them in with another layer of sand and mucus!
The female forms the collar under the sand and then forces it above the sand when done. The thousands of eggs develop in the the sand-mucus matrix. The process of making the egg collar takes 10 to 14 hours and reportedly starts at the beginning of a flood tide.
As long as conditions are good, the egg collars found on beaches are likely to have embryos developing inside them (if they are still rubbery and moist). When the egg collar is intact as you seen in the images above, the young have NOT hatched out. The collar disintegrates when the larvae hatch.
The larvae are plankton for 4 to 5 weeks and then settle to the ocean bottom to develop further. There is contradictory information on how long it takes the eggs to hatch (one reliable source relays about 1 week while another reports up to 1.5 months). The moonsnail species in the photo above is the Northern Moonsnail whose shell can be up to 14 cm wide (Neverita lewisii is also known as Lewis’ Moonsnail). Photos taken in British Columbia, Canada but there are moonsnail species, and their collars, off so many coasts.”
What has catalyzed my finally also adding this content to my blog is that Mickie Donley shared her video with me showing a female Northern Moonsnail pushing her eggs to the surface.
You might be wondering how a snail THAT big can fit into their shell. Through the rapid uptake of seawater, the foot of can inflate up to four times the size of what it is when in the shell The water is expelled when moonsnails squeeze back into their shells. They need such a big foot to dig for their clam prey AND for females to construct their egg collars below the sand.
With the entry to the shell having to be big, of course moonsnails need an “operculum”, a door-like structure that seals off the opening to the shell. See my “Shut the door” blog on opercula at this link.
Who drilled those holes? Moonsnails!
While some whelk species also drill holes into their prey with their radula (rough tongue-like structure), when moonsnail species drill holes into their prey, there is the sunken / bevelled edge you see here. Notice too how the hole is almost always near the “umbo” of their prey’s shell (highest part). That’s also a clue that the predator was a moonsnail species, not a whelk species. See bottom of my blog at this link for more information on the radula.
From Washington State’s Department of Ecology: “The average moonsnail takedown lasting 4 days as it drills ½ mm per day. In order to speed things up a bit, the moon snail produces hydrochloric acid and other enzymes to help dissolve the shell and liquefy the clam’s insides . . . Once a perfectly rounded hole is made in the shell, the moon snail inserts its tubular, straw-like mouth and slurps up the “clam smoothie” inside. It can take another day or so for the moon snail to ingest the clam innards. Talk about delayed gratification!”
Note that I have found moonsnail shells with holes drilled into them from . . . . a moonsnail.
Who goes there? I believe the tracks in my image below are from Northern Moonsnails.
Moonsnails clearly need to live in sandy habitats. It’s where their prey live and they also need the sand to make their egg collars.
Northern Moonsnail as shown in all the images above. Neverita lewisii is the biggest moonsnail species in the world (largest member of the Naticidae family).
Aleutian Moonsnail – Cryptonatica aleutica to 6 cm across.
Arctic Moonsnail – Cryptonatica affinis to 2.5 cm across.
Pale Arctic Moonsnail – Euspira pallida to 4 cm acrross.
Drake’s Moonsnail – Glossaulax draconis to 9 cm across and more common in California. Note that it is acceptable to use “moon snail” and “moonsnail”.
I feel better! How about you?
There, I feel relief now that I have finally been able to commit this information about moonsnails to a blog.
I considered entitling this “Moonsnails – the Gateway Mollusc”. Why? The Northern Moonsnail is one of the first species that erupted the lava of interest within me for marine invertebrates. It started with two mysteries: I found a shell with a perfectly round hole drilled into it and . . . I found the strangest, grey, round, seemingly cemented coils of sand.
Look where it got me. 🙂
I hope this added to your knowledge and appreciation for marvellous moonsnails.
More detail on moonsnail reproduction and feeding from Dr. Thomas Carefoot’s “A Snail’s Odyssey“
Reproduction: Sexes are separate in moon snails [Neverita lewisii] and sperm transfer is direct via a penis . . . The fertilised eggs are enclosed one to a capsule and extruded from the female in a mucousy mixture that is combined with sand (left drawing below).
The colour of the egg collar depends upon the type of sand and other inclusions contained within it.
Each egg/embryo rests in a jelly matrix within an egg capsule. Moon snail veligers range in shell length from 150-200µm. The unusual shape of the egg collar results from the extruded mixture being moulded between the propodium and the shell before it sets into its final sand/jelly state (left middle drawing below).
The extrusion and moulding take place under the sand, commence at the start of flood tide, and take 10-14h. After the initial moulding is finished, the female works over the egg-collar surface one more time adding a protective sheath of sand and mucus (Right middle drawing below) and, at the same time, pushing the collar upwards to the sand surface (right drawing below).
Development within the capsule to a swimming veliger larva takes a week or so, and it is possible that the capsular fluid is utilised as food. Simultaneous with the emergence of the larvae from their capsules, the sand-mucus matrix of the collar disintegrates and the larvae swim freely in the ocean.
Adult moon snails are strict predators and mostly eat bivalves. As many of their prey live at depths of up to 20cm or more, the snails have to burrow quite deeply to find them. Burrowing by moon snails is enabled by a large foot that is capable of inflating up to four times the shell volume through uptake of seawater. The inflation is quick, allowing fast penetration into and displacement of sand. The moon snail catches hold of its prey and hauls it to the surface to begin drilling.
Moon snails manipulate the shell of their bivalve prey so that the umbo is closest to the mouth. Whether this provides easiest handling, or whether it is to place the drill-hole directly over the bulk of soft body tissues, is not known. Another special feature of drill holes of Neverita lewisii is that they are countersunk. This feature allows the predatory records of the snails to be monitored more closely than that of, say, whelks (whose drill-holes are less distinctive). After a hole is drilled, the snail extends its proboscis hydraulically and commences scraping and eating the soft internal tissues with its radula, which is at the tip of the proboscis.
Lamb, A., Byers, S. C., Hanby, B. P., Hanby, B. P., & Hawkes, M. W. (2009). Marine life of the Pacific Northwest: A photographic encyclopedia of invertebrates, seaweeds and selected fishes. Madeira Park, BC: Harbour Publ.
Here’s a post about anemone enemies (say that 5 times).
See those really long tentacles extending from the Short Plumose Anemones in the following image? These are “catch tentacles” that can extend to be up to four times longer than the feeding tentacles.
Short Plumose Anemones reach around with these specialized, extendable tentacles and THEY ATTACK if they come in contact with a different species of anemone, or others of the same species who do not have the same DNA (are not their clones).
The tip of the specialized tentacle breaks off and kills the cells in the spot where they touch their anemone enemy. Apparently this can even kill the target anemone. Short Plumose Anemones on the outside of a group of related clones are more likely to use / develop these specialized tentacles.
Short Plumose Anemones AND Giant Plumose Anemones also have nematocysts (stinging cells in their feeding tentacles) AND they have acontia. See following image. These are defensive strands filled with stinging cells that are EJECTED from their mouths or through the anemones’ bodies when threatened or stressed. These threads extend far beyond the anemone and provide longer distance defence than the stinging cells.
None of the stinging cells of local anemone species impact we humans. But how I wish I had some acontia! Yes, I have defence envy. 🙂
From Invertebrates of the Salish Sea: ” Animals on the border of a clone often develop up to 19 “catch tentacles”, which generally occur close to the mouth. These tentacles, which are larger and more opaque than the other tentacles, have special nematocysts and are unusually extensible (they can become up to 12 cm long or more). They probe the area around the anemone. While they do not respond to food, they DO fire when they contact either A. elegantissima [Aggregating Anemone] or another clone of M. senile. When it fires, the tip of the tentacle breaks off and sticks to the victim, which may retract and bend away. Tissue damage can generally later be seen in the stung area, and the attacked individual may even die.”
These are Great White Dorids. Yes, they are a species of nudibranch and the individuals featured here are mating, prowling for sponges AND succeeding in laying their astounding egg masses.
EACH dot you see in the egg masses (photos below) contains 8 to 12 fertilized eggs. They are laid by both parents because it makes a lot of sense to be a hermaphrodite when you are a sea slug and your eggs hatch into the sea. More fertilized eggs = more chances of some young surviving.
Even after so many years, I find the intricacy and diversity of sea slug egg masses something of jaw-dropping wonder. Not such a good thing when you are supposed to hold a regulator in your mouth while diving. 🙂
Scientific name of this species is Doris odhneri. They can be up to 20 cm long and their egg masses can be at least that size too.
Body design is classic for the sub-classification of nudibranchs that is “the dorids”. Those tufts on their hind ends are the gills and the projections on their heads (which all nudibranchs have) are the sensory rhinophores (rhino = nose). It’s how they smell their way around to find mates, food and whatever else is important in their world.
Notice in the next photo how dorid species are able to retract their gills when disturbed by the likes of an annoying underwater photographer.
Amazing too to think of the importance of smell in the sea isn’t it? Why is the individual in the following photo reared up like that? I believe it allows a better position to smell / detect the chemicals of food and/or a mate. Maybe they are even releasing pheromones? Note that is me musing. There is no research I know of to support this.
In featuring this species, the Great White Dorid, you see that not all nudibranch species are super colourful. But they are all super GREAT.
Species is also referenced as the GIANT White Dorid or Snow White Dorid, or White Dorid or White-Knight Nudibranch . . . etc. Known range is from southern Alaska to California but it’s a species I don’t see often where I dive around northeastern Vancouver Island.
A female Giant Pacific Octopus hunting . . . photos brought to the surface for you on April 4, 2021.
This individual lives north of Port Hardy, in Browning Pass.
She’s a giant among other giants.
The Giant Plumose Anemones stand tall above her, at up to 1 metre in height.
Her arms feel between the rocks to flush out prey, her mind processing all she detects from her eight limbs, her vision, and the further stimuli upon her skin.
A China Rockfish is hovering nearby, likely often accompanying her when she is hunting to benefit from what prey emerges when touched by her arms.
Her colours change, flashing white at times. Then, again camouflaged among the boulders covered with the pink of coralline algae species, and studded with Orange Cup Corals and the plumes of feeding tentacles of Orange Sea Cucumbers.
Two humans are in awe at chancing upon her and being able to hover, navigating the space between not wanting to disturb and also wanting to amplify the wonder above the surface, hoping it somehow contributes to being better humans.
We’re aware too that we are limited by how much air remains in our tanks; the nitrogen building in our blood; and the cold creeping in through our dry suits (despite the adrenaline surge of watching her).
But she, she is limitless here.
She is perfection.
I know this was a female because the third arm on the right does not have a “hectocotylus”. Male octopuses have a specialized arm with no suckers at the tip called the “hectocotylus arm” by which they hand off spermatophores to the female. In Giant Pacific Octopuses, the hectocotylus arm is the third on the right. See more in my recent blog “Giant Pacific Octopuses, How Do They Mate?” at this link.
You can see that the pupil’s shape is very different from ours. Their retina is very different too.
Octopuses and other cephalopods have only one kind of photoreceptor cell while we have rod cells and three types of cone cells allowing us to see in colour. So how can cephalopods discern colour when they have only one kind of light receptor in their eyes? And they must be able to discern differences in colour. Consider how they signal with colour and how they camouflage.
Research from 2016 puts forward that their uniquely shaped pupils act like prisms, scattering light into different wavelengths (chromatic aberration), rather than focussing the light into a beam onto the retina. The hypothesis, tested with computer modelling, is that cephalopods can then focus the different wavelengths onto their retina separately by changing the distance between the lens and the retina, thereby separating the stimuli and discerning colour. Note that the sharpness of their vision is believed to be different for different wavelengths / colours.
Even with their eyes closed, octopuses can detect light with their skin. This is tied to their ability to camouflage with the photoreceptors in their skin responding to specific wavelengths of light (different wavelengths = different colours).
Note too that octopuses do not have eyelids. They have have a ring-shaped muscular fold of skin around the eye that closes in the way of an eyelid (especially when some annoying human is taking photos).
More Octopuses Hunting
Here’s the link to another experience where we saw a Giant Pacific Octopus hunting AND interacting with a Wolf-Eel (includes video).
Following on the success of my blog answering the important life question: “How do octopuses poo?“, it’s high time I address “How do octopuses mate?”
Why? Because truly, by having better understanding of the adaptations of species that look so different from us, I believe we can be better humans.
What has catalyzed this blog finally being written is the following video by fellow diver Mel Vincent with buddy Jerry Berry. On a night dive, what they thought was one Giant Pacific Octopus, turned out to be two AND evidence that they had likely mated. The evidence is the empty “spermatophores”.
Spermatophores? The name gives you a good sense of what those might be, they are the rope-like sperm packets of a male octopus.
This is most likely the female although in neither can the 3rd arm on the right be seen to confirm if there is a hectocotylus arm or not. Giant Pacific Octopuses are Enteroctopus dofleini, the largest octopus species in the world.
Male octopuses have a specialized arm with no suckers at the tip called the “hectocotylus arm”. In Giant Pacific Octopuses, the hectocotylus arm is the third on the right. The section at the top which has the spermatophores is called the “ligula”. This section does not have the cells that allows colour and texture to change (the chromatophores). So the males often keep it curled up which helps discern males and females i.e. look for a curled up arm.
The spermatophores are made inside the male and the male grabs them by passing the hectocotylus arm into his body through the siphon when it is go time. It’s not a fast process. Apparently it takes about an hour for the sperm to move to the top end of the spermatophore. The spermatophores pass down a grove in that arm helped by cilia. Ultimately the spermatophores are ejected by the ligula and the shape of the spermatophore (and swelling inside the female), lock it in place in the female.
Where to “deliver” the contribution to the next generation in a female octopus? Through her siphon, to her oviduct(s). The swollen end of the spermatophore then bursts and the female stores the sperm in her “sperm receptacle” till ready to fertilize and then lay her eggs. Reportedly, about 40 days after copulation (delivery of the spermatophores) the female attaches up to ~68,000 fertilized eggs to the top of the den she has chosen . . . to be her last.
Credit: Pierangelo Pirak Source: BBC article on octopus sex
In Giant Pacific Octopuses, a spermatophore can apparently be up to 1 meter long and contain over four billion sperm. Usually two spermatophores are involved in one copulation. Such large numbers of sperm, and eggs, are needed when your babies hatch into the soup of the ocean. But mother gives them a fighting chance. Read on!
The spent spermatophores apparently may hang from the female for a while so can it be known for sure that the two Giant Pacific Octopuses Mel documented had just mated, or mated at all? It can’t be known definitively but with there being two octopuses, and that they had been interacting, it does suggest that mating had occurred. It certainly is extraordinary to have chanced upon the spermatophores of wild Giant Pacific Octopuses.
When a female giant Pacific Octopus is ready to mate, it appears that she selects a den and attracts males to her. There is no conclusive evidence on how the female entices males, but there are strong indications that she produces some sort of chemical attractant. There are several reasons for believing this to be true.
The first reason is that giant Pacific octopuses are ordinarily solitary, and a smaller female would normally avoid a larger male that might attack and eat her. Jim has seen as many as nine males, however, in the immediate proximity of a female in a den. The males were scattered around the den and appeared to be unaware of each other, as there were no interactions amongst them. This was most unusual.
The second reason is that Jim has observed and seen video of large males standing atop prominent rocks. The octopus faces into the current and spreads out his arms like an open umbrella, turning slowly back and forth as the current flows past. We know that octopus suckers are sensitive chemical sensors, so it’s likely that the male tastes the water flowing past. His slow turning may enable him to identify the direction of the female’s attractant.
How the female selects a male—and whether she mates with one or more than one male -a re still unknown. Jim is currently working with a genetics professor at the University of Victoria to try to resolve these questions.
Once a female selects a male, there are several ways in which the male transfers sperm to her. Sometimes the male mounts the female, almost completely covering her. In other cases the male merely extends his hectocotylized third right arm into the fe male’s den. Although the actual transfer of sperm requires only two to four hours, the mating process can last several days, so divers have a considerable handicap when trying to observe such behaviour. Indeed it is a rare event to witness a mating pair, and Jim has only seen nine matings. This is one situation in which observations in an aquarium are far easier than those in the open ocean. An aquarium researcher can set up a video camera and organize teams to watch the process on a 24-hour schedule until the event ends.
Jim, along with three other researchers, has combined experiences from open ocean and aquarium observations to produce a publication about giant Pacific Octopus matings. The study revealed that the male and fe male mate for approximately four hours and that repeat matings have been observed. In aquariums there is usually only one male in the tank with the female, so questions about multiple males and how the female selects a particular mate remain unanswered.
The male passes the female an elongated package of sperm called a spermatophore, which may be up to one metre (three feet) long, which he deposits in one of the female’s two oviducts. It is believed that when mating the male actually places two spermatophores in the female, one at the entrance to each oviduct. At this time the female is not yet pregnant—the term really does not apply to invertebrates anyway—but she has stored the sperm and will head off to find a suitable den to lay her eggs. The male, if he still has unused spermatophores, may try to find another female.
Thę den the female selects is usually deeper than 20 m (66 ft). Jim has noted that dens where previous females have nested were reused 41 percent of the time. These preferred dens tend to be under large flat rocks that provide a suitable overhead surface for the female to attach her eggs.
Once the female selects the den, she sometimes fortifies it by gathering rocks from the surrounding area and dragging them to the den. She often piles them up to create a wall of boulders that keeps out predators. A few days to a month may elapse between mating and selecting and preparing a den.
LAYING THE EGGS
Now the female begins to lay her eggs. She turns upside down and clings to the roof of the den while she lays the tiny eggs one at a time. Each egg is produced in the ovary and coated with rich yolk to provide energy for the developing embryo. At this point some sperm is used to fertilize the egg, and it is coated with a material that hardens into a rubbery, semi-opaque shell. Each egg is extruded individually through the funnel and grasped by the small suckers that surround the mother’s mouth.
The body of the egg is a mere six millimetres (0.2 in) long about the size of a grain of rice—with a slender tail that adds another 11 mm (0.4 in), making the total length of the egg about 17 mm (0.7 in). The mother’s small suckers deftly manipulate the tail of the egg along with the fails of other eggs and weave them together into a slender string. She produces a secretion and applies it to the tails to bind them together. Over a period of three or four hours, while hanging upside down, the female produces a string containing an average of 176 eggs. Having glued this string to the roof of the den, the female descends to rest before returning to lay another string.
Eventually, over 28 to 42 days, the female will produce a complete nest of about 390 strings with approximately 68,000 eggs.
Once the female has finished laying, she spends the next 6.5 to 11 months tending the eggs. She grooms them with her suckers to ķeep them free of bacteria and other organisms that might damage them. Usually she is not completely successful, as often some eggs are encrusted by colonial animals called hydroids and do not hatch.
The female blows water through the strings of eggs with enough force that they jostle around. This helps keep them clean and free of growth and will be critical when the eggs start to hatch. She also protects the nest against predators such as sea stars, not always successfully. Mottled sea stars (Evasterias troschelii) have been observed robbing egg strings from a den.
Video above by Laura James of a mother Giant Pacific Octopus tending her eggs.
Other creatures enter the nest but do not appear to do any damage. These include small worms, snails and crabs such as the longhorn decorator crab (Chorilia longipes) and the sharpnose crab (Scyra acutifrons).
While the female tends her eggs, she does not feed. We don’t know the exact reason for this, but one suggestion is that if the female left the den to hunt, she would leave the eggs unat tended and vulnerable to predators. Another suggestion is that the presence of food scraps in or near the den might attract predators. Jim does not subscribe to either of these theories. Because this behaviour is common to many cephalopods, he believes it is more likely linked to an ancestral trait, the reason for which may no longer exist. This is an example of innate behaviour, part of the hard-wired information an octopus is, born with.
The development of the embryos depends on the surrounding water temperature. The colder the water, the slower the develop ment; the warmer the water, the faster it proceeds. This is true among most egg-laying marine invertebrates.
Jim has been able to observe much of the development in the wild and develop a time frame for estimating when hatching would occur. If he was lucky enough to have witnessed the egg laying, he would have a pretty accurate idea of how the eggs would look as they developed. In most cases he did not see the egg laying, however, and would have to observe the eggs for signs of development to predict when they would hatch.
WATCHING THE EGGS: A DIVER’S VIEW
Newly laid eggs are glossy white and look like white raindrops. The core that the eggs are woven into is pale green, but within a few weeks the core turns black and remains so.
Two small red dots appear on each egg about 120 to 150 days after the eggs are laid. These dots, the developing eyes of the embryo, are visible through the egg shell. The eggs are no longer as shiny white, and soon one can see the brighter yolk sac in the large end of the egg and the darker developing embryo at the small end.
About 180 to 210 days after the eggs are laid, the embryo has used up much of the yolk, and the size of the yolk sac has de creased while the size of the embryo has increased. So that the embryo can continue growing, it moves into the larger portion of the egg. This is actually the second reversal, but it is the only one that a diver can observe.
Over the next few months a diver can watch as the yolk sac becomes smaller and the eggs become darker. Those with sharp eyes may be able to see the movement of the embryo within the egg and the flashing of brown and white colours as the embryo tries out its chromatophores.
About 240 to 270 days after the eggs are laid, hatching occurs.
It might seem logical that the eggs would hatch over the same period of time and in the same order as they were laid. This does happen in many octopuses, including the giant Pacific octopus, but not always. Jim has witnessed a number of hatchings in which he has seen the nest intact one day and completely hatched out the next morning.
Jim collected strings of unhatched eggs from time to time and took them to his lab. When observing the eggs through a dissect ing microscope, he found that the water surrounding the eggs was warmed by the microscope lights, often causing the eggs to hatch. He probably collected strings of eggs that had not been laid at the same time, yet even eggs from different strings hatched nearly simultaneously.
Some type of chemical released from a hatched egg stimulates other eggs to hatch as well, Jim suspected. The embryos often had different amounts of food remaining in the yolk sac below their mouth. In some cases the yolk sac was consumed, but in others the yolk sac was still large enough that the paralarva had to bite it off. Clearly some of the paralarvae were not as well developed as others but were able to survive even if they hatched somewhat prematurely.
The hatch normally occurs at night. It may start at dusk, but often it is several hours after dark before things really get under way. As the eggs hatch in ever-increasing numbers, the female blows strongly onto the strings of eggs, causing them to thrash around. This helps the paralarvae to pop out of the eggs and aids in flushing them away from the den.
MOTHER’S JOB IS DONE
In most cases the female survives the hatching and lingers in the den for another few weeks before she dies. During the entire nesting period, which may have dragged on as long as 11 months, the female has not eaten. By hatching time she has lost more than 60 percent of her body weight, sometimes as much as 85 percent! Even though the eggs have hatched the female continues to “mother” them as before. She grooms the hatched-out egg cases even though the paralarvae are long gone.
Experiments have been done in which the eggs have been re moved from the ovary of a mated female. Incredibly the female went through the entire egg laying and grooming process, even though she had no eggs or nest. This “phantom nesting” shows that a behavioural lock and key is triggered at sexual maturity or at mating.
In some cases the female does not have enough energy stored to survive the whole nesting period and dies before the eggs hatch. Usually her last act is to vacate the den and crawl away. She usually only moves a metre or two before she dies. Again there is no solid evidence on why the female va cates the den, but Jim sub scribes to the theory that if the female died in the den her de composing body could foul the water and attract scavengers.. One can understand that fe males not leaving the den might have resulted, in an evolution ary sense, in the nest being dis covered and eaten. This would result in the failure of her genes to be passed on to successive generations. The genes that were passed on would be those of females who successfully distracted predators away from the nest.
While this strategy is interesting, it is not totally successful. In several cases where the female died before the eggs hatched, even though the embryos developed properly, the eggs did not hatch. Without the agitation provided by the female blowing wa ter over them, the closely packed eggs remain immobile and pressed against each other. As a result the paralarvae are unable to force their way out of the eggs, and most perish.
Jim found it sad to observe nests where only a partial hatch was successful. As he counted strings and eggs, he often found thousands of dead paralarvae. Sometimes nature seemed harsh and wasteful.”
Video below by Laura James of Giant Pacific Octopuses hatching and mother dying.
Male anatomy on left and female on right. Source: Hanlon, R., & Messenger, J. (2018). Reproductive Behaviour. In Cephalopod Behaviour (pp. 148-205). Cambridge: Cambridge University Press. doi:10.1017/9780511843600.008
Further detail on mating in Giant Pacific Octopuses from “A Snail’s Odyssey”
“After a short courtship, the male Enteroctopus dolfleini grabs the thin or distal end of a spermatophore from its penis using the groove in its hectocotylus arm and thrusts it into the orifice of one of the female’s oviducts. This initiates a complex series of events within the spermatophore that cause the sperm rope to be pushed into the thin or distal end, which swells to accommodate the incoming load of sperm and leads to evagination of the ejaculatory apparatus (see illustration on Left). This action locks the sperm-filled swelling in place within the oviduct and prevents it from dropping out of the female. The sperm rope is moved along by pressure from seawater diffusing into the proximal end of the spermatophore and from elastic contraction of the sperm rope itself.The movement takes about an hour. These actions haul the entire mass of tightly encapsulated spermatozoa over a distance of a meter from the proximal to distal end of the spermatophore. The sperm are now positioned in a swollen bladder or reservoir located at what was previously the thin or distal end of the spermatophore (see photograph on Right). The next step, evagination of the ejaculatory apparatus, occurs suddenly and produces a crink in the tube that locks it in place in the oviduct. The locking-in may additionally ensure that spermatozoa are not lost in “back-flow” from the oviduct. The swollen end of the spermatophore now bursts and the sperm are moved into the female’s sperm receptacle for later use. The process is repeated with a second spermatophore. About 2-3h after the arm is first inserted and after repeated pokings, the female has two empty spermatophores hanging from its oviducal orifices.”
[Note: Text below has been corrected / edited on January 5th. Corrections are marked in red.]
Marine snails have doors. Freshwater snails do too.
Some tubeworm species have them as well.
Yes they do.
They all make an “operculum”. That means “little lid” in Latin but, I’m sticking with referencing the structure being like a door. 🙂
See the operculum in my photo of an Oregon Triton below? It’s the structure sealing off the entrance to the shell.
Oregon Triton (Fusitriton oregonensis). That’s a Sunflower Star on the left. With that species now being in such trouble, it’s a clue that this photo was taken before the onslaught of Sea Star Wasting Disease.
Oregon Tritons are a big marine snail species with a shell up to 15 cm long (and with a range well beyond Oregon ie. known from northern Alaska to northern Mexico, and Japan). You can imagine how, if the snail did not have the operculum, a predator could still get access to the snail in its shell.
Lewis’ Moonsnails are another really big snail. Their shell can be up to 14 cm wide and look at the size of their bodies relative to the shell!
Lewis’ Moonsnail on the prowl (Neverita lewisii).
Even though they can release some water from their bodies to become smaller, they clearly need a big opening (aperture) to their shell to get back in.
It’s a space you do not want to leave wide open. Hence, the need for making an operculum to seal that opening.
Operculum from a Lewis’ Moonsnail. Shape, strength and size is perfect to seal off the entrance.
For snail species that may be found in the intertidal zone, closing the shell with the operculum not only protects them from potential predation, it also may offer them some protection from drying out. Greg Jensen, author of Beneath Pacific Tides, thankfully offered the following knowledge correcting my previous statement about how useful the operculum might be for this purpose: “Marine snails don’t generally use their operculum to seal the shell at low tide. They snug themselves up tight to a rock with their foot.”
He also shared that land snails, who do NOT have an operculum, avoid drying out by coming out in the cool of night or when it is otherwise damp. Another adaptation is that, when it gets too dry, they glue their shells onto a hard surface, sealed shut with dried mucous to retain moisture.
Not only does the snail make this shell-like structure, it also grows with the individual. The operculum is attached to snail’s body so when the snail retreats, the door does its job. Not surprisingly, the shape of the operculum is a match for the size and shape of the opening, therefore varying between species. The three photos below show some differences.
Blue Topsnail with operculum (Calliostoma ligatum, shell to 3 cm across). Even really tiny marine snail species like Common Periwinkles have an operculum.
Leafy Hornmouth closing up with the operculum visible at the end of the snail’s foot (Ceratostoma foliatum, shell to 10 cm long). There’s a Three-Line Nudibranch on the upper right.
Purple-Ringed Topsnail with opecullum visible (near a Green Urchin). Calliostoma annulatum, shell to 4 cm wide)
But what about hermit crab species who use the snails’ shells once they die? Since the operculum was attached to the body of the deceased snails, are the hermit crabs left with a wide open door? Oh just look at how amazing nature is in making sure they too are protected within the shell. The photo below shows you why so many marine hermit crab species have one claw bigger than the other. The bigger claw seals off the entrance in lieu of the operculum!
Widehand Hermit in the shell of an Oregon Triton. Widehand hermit is Elassochirus tenuimanu.
Not all marine hermit crab species have this adaptation. Other options include choosing a smaller shell so you can “shake it off” and run like hell when threatened. It’s called the Taylor Swift strategy. I’m kidding! But let me know if you get the pop star word play.
I also mentioned that some tubeworm species make an operculum. See below. In the centre of the image there is a Red-Trumpet Calcareous Tubeworm (Serpula columbiana to 6.5 cm long).
Red-Trumpet Calcareous Tubeworm in the centre (Serpula columbiana to 6.5 cm long) with two Checkered Hairysnails (Trichotropsis cancellata to 4 cm long).
As a tubeworm, the species captures plankton drifting by with its crown (radioles). As the common name indicates, the operculum in this species is trumpet shaped. For the individual in the photo, the operculum is purple with white stripes.
I had initially stated that there’s a really good reason for this species to have the door and you are looking right at it. Those snails are kleptoparasites. “Klepto” as you likely know, means to steal (from ancient Greek). The Checkered Hairysnails use their long mouthparts (the proboscis) to try to suck up the food the worm captures before it gets to the worm’s mouth. HOWEVER, what I also learned from Greg Jensen is that the theft by the Checkered Hariysnails is apparently so stealth, that the tubeworm does NOT respond to their mouthparts by closing its operculum.
Thereby, the operculum may help these tubeworms protect their crown (and other body parts) but does not protect them from kleptoparasites.
Diversity matters. Language matters. I suspect you agree. ☺️
In this case it’s about sea stars. I am sharing with you because you are an important audience to help increase understanding.
Just off our coast, there are 31 species of sea star in the Class “Asteroidea”. I hope my compilation below gives a sense of that diversity. The photos are all of different species photographed by yours truly off NE Vancouver Island.
Yet, even major news outlets have reported on sea stars as if they are all ONE species (includes CBS and Phys.org).
Thirteen species in the above compilation from left to right: Top row: Vermillion Star (Mediaster aequalis), Morning Sun Star (Solaster dawsoni), Rose Star (Crossaster papposus). Second row: Leather Star (Dermasterias imbricata), Ochre Star (Pisaster ochraceus), Orange Sun Star (Solaster sp. A = undescribed species). Middle: Sunflower Star (Pycnopodia helianthoides). Third row: Bat Star (Patiria miniata), Painted Star (Orthasterias koehleri), Drab Six-Armed Star (Leptasterias hexactis). Bottom row: Spiny Red Star (Hippasteria phrygiana), Velcro Star (Stylasterias forreri), Striped Sun Star (Solaster stimpsoni).
Why does this matter?
Not only do different species of sea star have different ecological niches, but communication about them as if they are one species has greatly confounded the understanding of what is happening with Sea Star Wasting Disease (SSWD). When a few individuals of one species are seen, this has been extrapolated to text like “But now, the species is rebounding.”
Which species? Where? Did the individuals survive?
This sort of “collective” perception is also often reflected in comments on my social media posts. When I post about any sea star species, comments like the following often result: “Good to see “THE sea stars” are coming back.”
Yes, some species appear to be doing better since the onslaught of SSWD beginning in 2013 e.g. Ochre Stars. Other species do not appear to have been impacted much at all e.g. Blood Stars. But the world’s biggest species – the Sunflower Stars who help maintain kelp forests – are now recognized as Critically Endangered by the International Union for Conservation of Nature (see further information below).
The odds are already stacked against the appropriate learning about the conditions causing SSWD because it is happening in the dark, below the surface.
Blurring this group of extraordinary starred animals into all being the same, risks an even greater loss of understanding, colour, diversity . . . and action. 💙
Further content about the IUCN designation from my post on social media:
It’s official and so important to know. The iconic, world’s largest sea star species, the Sunflower Star, has now been added to the International Union for Conservation of Nature (IUCN) list as Critically Endangered.
This is no surprise to those of us who have been monitoring their health but to many, Sea Star Wasting Disease is unknown, even though it is one of the biggest known wildlife die offs in recorded history.
It has happened largely out of sight, beneath the Ocean’s surface. Further, there are many of us who do not have enough understanding / appreciation of (1) the connection between land and sea and; (2) the different sea star species and their ecological importance. Seeing sea stars of other species does not mean that all species are okay. Sunflower Stars (Pycnopodia helianthoides) definitely are not.
It is positive that they have been officially “listed”. With this recognition of how at risk they are, there is better potential for resources and action to find out what has caused the die off and what this might be indicating about changing environmental conditions. There is the hope that more people will care.
This is an international designation. The species also needs to be assessed in Canada to determine “status” and potential protection / action under the federal Species at Risk Act.
“Populations . . . experienced dramatic crashes in response to a marine wildlife epidemic event – referred to as sea star wasting syndrome – that began in 2013. Using over 61,000 surveys from 31 datasets, The Nature Conservancy and expert ecologists at Oregon State University calculated a 90.6% decline in the global population of sunflower sea stars due to the outbreak and estimated that as many as 5.75 billion animals died from the disease . . . “The rapid decline of this giant sea star, and of the sea kelp forests that it helps preserve, highlights the importance of every single species on the IUCN Red List of Threatened SpeciesTM. Its entry into the IUCN Red List in the highest threatened category emphasizes the need for urgent action to understand and combat the wasting disease that is sweeping through the population. We hope that this listing leads to positive action and recovery for this species and its ecosystem,” said Caroline Pollock, Programme Officer for the IUCN Red List Unit. Sunflower sea stars are now nearly absent in the contiguous United States and Mexico. No stars have been observed in Mexico since 2016, none in California since 2018, and only a handful in the outer coasts of Oregon and Washington since 2018. They are still present in Puget Sound, British Columbia, and Alaska, but only at a fraction of their former population in most places.”
Oh how did I get to be today-years-old without knowing of this Robert Service poem that is so timely and speaks for a limpet?
His poem “Security” includes:
So if of the limpet breed ye be, Beware life’s brutal shock; Don’t take the chance of the changing sea, But – cling like hell to your rock.
Full poem is below which includes life lessons about taxi-crabs 🦀
Keyhole Limpet which I photographed near Port Hardy. Diodora aspera builds a shell up to 7.6 cm across.
There once was a limpet puffed with pride Who said to the ribald sea: “It isn’t I who cling to the rock, It’s the rock that clings to me; It’s the silly old rock who hugs me tight, Because he loves me so; And though I struggle with all my might, He will not let me go.”
Then said the sea, who hates the rock That defies him night and day: “You want to be free – well, leave it to me, I’ll help you get away. I know such a beautiful silver beach, Where blissfully you may bide; Shove off to-night when the moon is bright, And I’ll swig you thee on my tide.”
“I’d like to go,” said the limpet low, “But what’s a silver beach?” “It’s sand,” said the sea, “bright baby rock, And you shall be lord of each.” “Righto!” said the limpet; “Life allures, And a rover I would be.” So greatly bold she slacked her hold And launched on the laughing sea.
But when she got to the gelid deep Where the waters swish and swing, She began to know with a sense of woe That a limpet’s lot is to cling. but she couldn’t cling to a jelly fish, Or clutch at a wastrel weed, So she raised a cry as the waves went by, but the waves refused to heed.
Then when she came to the glaucous deep Where the congers coil and leer, The flesh in her shell began to creep, And she shrank in utter fear. It was good to reach that silver beach, That gleamed in the morning light, Where a shining band of the silver sand Looked up with with a welcome bright.
Looked up with a smile that was full of guile, Called up through the crystal blue: “Each one of us is a baby rock, And we want to cling to you.” Then the heart of the limpet leaped with joy, For she hated the waters wide; So down she sank to the sandy bank That clung to her under-side.
That clung so close she couldn’t breath, So fierce she fought to be free; But the silver sand couldn’t understand, While above her laughed the sea. Then to each wave that wimpled past She cried in her woe and pain: “Oh take me back, let me rivet fast To my steadfast rock again.”
She cried till she roused a taxi-crab Who gladly gave her a ride; But I grieve to say in his crabby way He insisted she sit inside. . . . So if of the limpet breed ye be, Beware life’s brutal shock; Don’t take the chance of the changing sea, But – cling like hell to your rock.
I ensured this is indeed Robert Service in all his glory by ensuring it was in the “The Complete Works of Robert Service” (1945) but could not find further detail on when he wrote it.
Don’t you hate when people use a provocative “hook” to get you to read their material? Yes, that’s what I’ve done but I promise you, it is worth it.
While I think all of us are a little unstable right now, this blog is not about me. It’s about the astounding adaptations of a little limpet assigned the name of “Unstable Limpet” (Lottia instabilis).
Unstable? This species just limpetted along on its own evolutionary path!
Most other limpet species are shaped so they can suck down securely on a FLAT surface for protection This works well because these most often graze on algae encrusted rocks. But the Unstable Limpet can secure to a ROUNDED surface.
Which rounded surface? Oh I will never forget the first time I noticed this species and realized the marvel of the adaptation. Unstable Limpets are shaped to be able to hunker down on the cylindrical stipes (stem-like structures) and holdfasts of the kelp species upon which they also feed!
I suspect that, like their flat-shelled brethren, Unstable Limpets have a specific spot to which they “home” and where their shell fits perfectly.
As is supported by others’ observations, I have found Unstable Limpets living / feeding on Old Growth Kelp (Pterygophora californica) and Split Kelp (Laminaria species).
I hope that this little limpet leads to you reflect anew on the wonder of the natural world around us and . . . about how being “unstable” just might mean being better adapted to the conditions you are in. It may even be of benefit in having a unique place and perspective in the world. 🙂
Below are further details about the species and an explosion of my photos documenting them.
Size: To 3.5 cm across
Known range: Northern Alaska (Kodiak) to Southern California (San Diego) from the intertidal to 73 metres depth.
Variation: Greg Jensen reports that: “Some members of this species settle on rocks, where they develop a more conventional limpet sharp and are difficult to distinguish from other limpets. This rock form was previously known as Lottia ochracea.” (Source: Jensen)
Behaviour: If touched by predatory sea star species, the Unstable Limpet “vigorously” runs away. Predatory sea star species referenced in the study are Six-Rayed Stars( Leptasterias hexactis), Sunflower Stars (Pycnopodia helianthoides), and Ochre Stars (Pisaster ochraceus ). It was unclear to me from reading a summary of the research (and being unable to find the original paper) if this response behaviour is different if the Unstable Limpet is on its “feeding scar” (a bit of an indentation in the surface of the kelp). It may be that it responds then like the Seaweed Limpet (Discurria insessa) which “usually responds to contact by elevating its shell (“mushrooming”) and rocking from side-to-side, but rarely moving away from the scar.” (Source: Snail’s Odyssey).
The following photos offer additional perspectives on two of the individuals shown in photos above.
Jensen, Gregory C, Daniel W. Gotshall, and Miller R. E. Flores. Beneath Pacific Tides: Subtidal Invertebrates of the West Coast. , 2018. Print.
Lamb, Andrew, Sheila C. Byers, Bernard P. Hanby, Bernard P. Hanby, and Michael W. Hawkes. Marine Life of the Pacific Northwest: A Photographic Encyclopedia of Invertebrates, Seaweeds and Selected Fishes. Madeira Park, BC: Harbour Publ, 2009. Print.
[Update: Species corrected thanks to Greg Jensen. I initially posted that the crab in the first 3 photos was a Moss Crab].
How do crabs make bad choices?
Let me show you via my photos and a “conversation” with the crab in the next three photos.
Oh hello mature male Sharpnose Crab. I almost didn’t see you there!
Please may I take a photo of how you have fabulously decorated yourself to camouflage against predators, using bits of algae, sponges, tunicates and hydroids?
It’s fascinating how your species, and others who decorate themselves, have little hooks (setae) on your exoskeleton to which attach life from around you AND that you change outfits when your change backgrounds. Do you sometimes also use the camouflage as easy-to-reach snacks?
Oh, oh! Wait!
You don’t know you are walking onto the head of a Red Irish Lord, an ambush hunter who is extraordinarily camouflaged too.
Careful! You are on the menu for this fish species.
The Red Irish Lord will try to grab you, ideally from the back of your shell. That’s what happened to the crab in the next two photos.
Indeed, that’s the same species of fish. Red Irish Lords have incredible diversity in colour to blend in so that you, and I, have great difficulty detecting them.
When the fish does not have the advantage of a sneak attack, you can defend yourself by spreading out your claws really wide. Like what you see below.
Then, it’s difficult for the Red Irish Lord to fit you into his / her mouth.
Yes, I too imagine the crab in the above two photos saying, “You want a piece of me?!”
It’s said of your species that you “put little effort into decoration”. Such judgement!
In another species, the Moss Crab, a correlation has been found between size and how much decoration there is. Once big, especially with claws spread wide, mature male Moss Crabs cannot easily be gulped up whereby there is less need for camouflage. But mature male Moss Crabs are huge! Up to 12.3 cm just across their carapace. Your species, the Sharpnose Crab (Scyra acutifrons) is only up to 4.5 cm across the carapace. Mature males of your kind have a far greater reach with their claws than mature females.
By the way what’s with the posturing with mature males of your kind when they do what is shown in the photo below?
Yours is NOT the only crab species that can be gulped up. I think it might be a Graceful Kelp Crab who has been engulfed by the Red Irish Lord below.
Below is another crab in danger of making a fatal choice as it advances down the face of the Red Irish Lord. See how precarious this is? The fish will remain motionless, waiting, waiting till you are in the ideal position to ambushed from behind. Then your claws are of little use to you.
There you go dear human readers.
I do not know the fate of either of the crabs on the heads of the Red Irish Lords. I had to return to the world where we humans can also make really bad choices.
Why no, my referencing human bad choices on November 4th 2020 is purely coincidental. Insert innocent eye batting here. What choices could I POSSIBLY be referencing? ☺️
Be kind. Be colourful. Be careful. Be truthful. Be safe. 💙
Regarding the photo above, see the Red Irish Lord and the two crabs with outstretched claws?