Here are a couple of great links pirated from the Deep Sea News blog.
The subject of that blog’s discussion is what the author calls “sea angels,” rather beautiful predatory swimming snails in the genus Clione. Embedded below is a movie of one swimming lifted from YouTube. These pretty liddle snails were called “sea butterflies” in the Pacific NW – off the British Columbia and Washington coasts, where I had many chances to observe them, both during and after my graduate studies.
In that area, the common species reaches lengths of about 2 cm – 3cm, roughly an inch or so, but most of the individuals I have seen have been smaller. These are shell-less snails, found in the water of the colder oceans through out the world. They swim all their lives.
“Sea angels” and “sea butterflies” ….. ah…. such cute names…
Sorta like calling a hunting tiger, “Fluffy,” or a semi-starved, very hungry, fresh-from-hibernation-and-in-a-(REALLY)-bad-mood Grizzly bear, “Snuggles.”
Individuals in Clione species snails are specialized predators that appear obligately bound to eat only another pelagic swimming snail. At least that is the reading from the snail biology gospel; in reality I don’t think they have been studied well enough to know if they have any alternative prey. While Clione individuals lack shells, their prey do have shells and look rather like a regular snail; both species have large extensions of their foot which they flap like wings. This gives all of these snails the group name of Pteropods, or “wing-foot,” snails.
I have embeded another movie, this one showing Clione individuals attacking and eating their prey, Limacina. And as you watch the movie, I think you will see why I consider the name of Sea Angel to be a bit…. inappropriate. Unless, that is, it is modified to be the “Sea Angel of Death.”
Swimmers near bathing beaches should be thankful that Clione individuals don’t reach about 2 m long (6.6 ft) and have a taste for humans.
A few times when I was teaching a course about Marine Invertebrates at a university field station/marine laboratory on Vancouver Island, I was lucky enough to be able to have had my theaching assistants collect some individuals both Clione and Limacina within a day or two of one another. For the class, I would take a large graduated cylinder – these are about 3 feet long and several inches in diameter. And then I would put in one or two Clione individuals and let them become acclimated, typically that only took a minute or two. Then I would have the students gather around, and would introduce two or three Limacina. The rapidity and apparent “ferociousness” (this is a anthropomorphic adjective, but after watching the Clione at work, it seemed to fit, but probably a better adjective is “efficiency”) of the attack would typically leave the students, quite literally, speechless.
Most of the time marine biologists (and I suppose other folks who see such things) typically regard snail predation as a slow and rather leisurely process (albeit animals like Cone snails will also demonstrate the other extreme). After all, an oyster drill (a muricid whelk) drilling a hole through a bivalve shell is hardly action that is exciting, except, perhaps, to the participants.
Then, if you are very lucky, you get to see something like Clione attacking a Limacina. Wow!!! It kinda blows away the stereotypes and misconceptions…
If you think about this system, wherein one pelagic snail lives by preying only on another pelagic snail, a bit further, I think it is really cause for wonder. At best, Clione – the predators – are found in aggregations (I really don’t think one could call them “schools,” or “herds” or “flocks”) or patches maybe several meters in volume, and with a few snails per cubic meter. More often the patches arel larger a few hundred meters on a side, and the density is one or two snails per 5 or 10 cubic meters.
So… lots of water… not many predators….just swimmin’ along being their little sea angelic selves, and with a LOT of water between them.
Now… the prey – and the same sort of situation. Lots of water, not many prey.
Two diffuse patches of animals in a very large body of water, what are the odds that any one snail of either species will encounter an individual of the other species?
Well, the odds have to be pretty good or the animals wouldn’t be here! But still, it is not like these are pedestrians on the sidewalk along a busy street bumping into one another.
I don’t know of any research that has been done investigating these interactions ecologically in nature. I suspect the logistics of such research would make it prohibitively expensive (lots of ship time, for example), but the questions raised by the necessity of such interactions are really pretty interesting, I think you will agree.
Perhaps they are being studied at the present. The author of Deep Sea News blog mentions a student/researcher/photographer, Natalia Chervyakova of Moscow University, who has taken some images of Clione feeding in nature – an amazingly difficult proposition. Here are some of her images from the White Sea. These are some of the most spectacular underwater macro photographic images I have ever seen. And having taken thousands of underwater shots, including a number of planktonic macro shots, I can attest to the skill and effort involved and demonstrated by these images. I would have killed to have been able to get one – 1 – image like these. I would have killed a lot more, to have had the skill to be able to do it repeatedly.
Finally, shelled pteropods, similar to Limacina in some regards, are at the base of the zooplankton food chain throughout much of the world’s ocean. They are especially abundant in the very rich fishery regions of the cold temperate and boreal seas, where they eat phytoplankton and convert it into their tissue. In turn they are eaten by many other organisms. Two or three times removed, they are the fish flesh or krill that is harvested for human consumption or use, to say nothing of the top predators in those ecosystems, whose trophic position has been usurped by humans. These pteropods have aragonitic shells, and as the oceans acidify they will be amongst the first to be affected by this interesting tiny experiment in the alteration of the ocean’s physical parameters. “Affected” … A nice polite word for “Exterminated” by both human action (the addition of massive amounts of excessive carbon dioxide to the atmosphere) and inaction (no attempt to slow down those additions).
The sheer and utter stupidity of the human species, both individually and collectively is truly mind-boggling. Here we are, well on our way into the sixth major mass extinction event in the Earth’s existence, and politicians play games of posturing over public images and the majority of the public wastes its time paying attention to the foibles of ephemeral pseudo-entertainer or some ridiculous sporting event. I guess over the symbolic grave of humanity, our epitaph should be, “Considering their potential and abilities, they had their priorities straight.”