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 protect moonsnail 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.
Other moonsnail species?
There are five species of moonsnail that range from Alaska to southern California or northern Mexico.
- 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“
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.
Carefoot, Thomas. A Snail’s Odyssey
- Moonsnail feeding
- Moonsnail reproduction
- Moonsnail locomotion
Gronau, Christian – Cortes Museum blog; The Biggest Moon of All
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.
Washington State Department of Ecology – We’re over the moon for the moon snail