Posts Tagged ‘predation’

Predators In The Sand, Or…

Monday, September 5th, 2011

Thoughts On The Evolution And Natural History Of Scaphopods.

Why Here And Why Now?

This post is, obvously, the continuation of a series dealing with scaphopods and some  of the data I will be posting subsequently are also to be found on one or another of my website’s scaphopod pages.   However, these blog entries are not strictly duplicative; I have added a number of new data and I have  altered some of  the information to reflect my present thoughts.   Some of the ideas and data to be  presented here are somewhat iconoclastic, and contrary to what some authorities have proposed.  It is unlikely I will get the opportunity to publish these ideas in more formal, peer-reviewed, jounals, and as a result I thought this is an appropriate place to let the ideas see some glimmer of the light of day, albeit dimly and through some wet mud.  To the questions of “Why Here and Why Now?”  I think the reasonable answers are, “Because I think  this is an appropriate place and it is time.”  Or phrased another way, “Why Not?”

 One of Three Groups…

The scaphopods are the last of the classical molluscan classes to show up in the fossil record, with arguably the first unequivocal scaphopod being Rhytiodentalium kentuckyesnis Pojeta & Runnegar, 1979.  However, this unequivocality is not likely the case; the specimens of Rhytiodentalium are all significantly altered fossils, and from personal examination, it is impossible to tell exactly what they are.  Although some of them match the general shape of modern – and presumably – highly derived scaphopod shells, these “shells” appear to be comprised of small pelletized material.  It is unclear if these pellets are the result of significant or minor diagenesis.  In the first case, the shells could considered as scaphopods.  In the second, they would have to be something else, perhaps, some sort of worm tube.  I think the latter is much more likely than the former.

The term “armchair quarterback” has been coined to describe those individuals who after watching a football game at home on the “aptly-named” boob tube, dissect a quarterback’s performance and describe, a posteriori, what he should have done.   Of course, such a critique, if that’s what it may be called, is done without the experience of being under the tremendous pressure of the momnet on the field of play, without the sport’s equivalent of the “fog of war” clouding information input and, most importantly, it is done with the precision vision of hindsight.  Of course, in the armchair experience, errors made on the field become glaringly obvious.   One of the prime theories of scaphopod evolution is that scaphopods arose from an ancestor that either was in the extinct class, Rostrochonchia, or pehaps in its ancestral group, is the malacological equivalent of such airchair quarterbacking, however, with one glaring exception.  It is undoubtedly wrong, most likely as a result of being proposed by individuals who have had no experience examining or studying live scaphopods or, indeed, live animals of any sort..

There are a number of very serious problems with the Scaphopods from Rostroconchs derivation, not the least of which is that the scaphopod shell is univalved and tubular, while the rostroconch shell is bivalved of various non-cylindrical shapes.   Additioanally, the scaphopods are all predators or scavenger/predators; as a result, they must move; no predator on infauna waits for the prey to come to it.  Then, the scaphopod radula, the structure used to macerate, break, crush  or smash prey is the largest radula relative to the adult body size in all the mollusca.  On the scale of the organisms, it is a truly massive structure.   This massive radula is presumed to have been derived from an ancestor in the same group that is supposed to have given rise to the bivalves.  However, not only do the bivalves  lack the radua, but also any remnant of the head it is found in.  While the scaphopod head is reduced and kept within the shell, it is present, and has a relatively large brain, also a structure missing in the bivalves – and presumably their rostroconch ancestor.  The rostroconch shapes vary quite a bit, but one thing that is evident in all of them is that they are not streamlined and capable of easy movement through sediments.   Indeed, with the shapes typically found  in rostroconchs, it is quite likely, that like some oddly shaped infaunal bivalves today, they did not move at all as adults.  Scaphopods, on the other hand, are all mobile and many of them, given the appropriate stimulus, are capable of bursts of relatively rapid motion, after which they often stop, construct a feeding cavity and feed.  Given the sizes of the adult scaphopods, the  number of body lengths that they are able to move in any given amount of time, and the media that they move through, it is quite reasonable to consider many of them to be “high speed” predators.  Finally, recent molecular genetic work shows them to be grouped with the cephalopods, not the bivalves.

I think it is likely that one of the first branchings of the ancestral molluscan stock gave rise to a predatory organism that had a tendency to develop or elongate in a dorso-ventral direction.   In turn, this ancestor, over time, gave rise to three successful clades, eventually leading to the crown groups of the cephalopods, gastropods, and scaphopods.  All of these groups are all characterized by dorso-vental flexing in the visceral region, a well-developed radula, and elaborations of the cephalic tentacles.

Each of the three dorso-ventrally flexed groups shows particular adaptations and modifications for its primary habitat.  The cephalopods are highly successful predators in the pelagic enviroment.  Gastropods have radiated into virtually every possible niche except aerial flight, and are found in all terrestrial, fresh-water, and marine environments, although their ancestral habitat was the marine benthic epifaunal environment.  Scaphopods have become highly adapted for predation on organisms living in unconsolidated marine benthic sediments.

Cadulus tolmiei in situ, modified from Poon, 1987.

The above image shows Cadulus tolmiei feeding in sediment, cb= captacular bulb, dd= digestive diverticula, fc = foot cavity, g = gonad,  m= mantle,  pa = posterior aperture,  s = shell,


Pojeta Jr., J. et. al. 1972. Rostroconchia:  A New Class of Bivalved Mollusks. Science. 177: 264-267.

Poon, Perry A. 1987. The diet and feeding behavior of Cadulus tolmiei Dall, 1897 (Scaphopoda: Siphonodentalioida). The Nautilus: 101: 88-92.

Steiner, G. and H. Dreyer.  2003.  Molecular phylogeny of Scaphopoda (Mollusca) inferred from 18S rDNA sequences: support for a Scaphopoda–Cephalopoda clade.  Zoologica Scripta. 32:343-356.

More to come…

Until then,


Sky Sharks And SCUBA

Sunday, December 19th, 2010

Hi Folks,

My wife and I got treated to quite a show yesterday.  For several hours, a male prairie falcon was cruising around our yard hunting doves.   These latter birds are Eurasian collared doves, one of several introduced pest birds (think large white/gray/tan pigeons) found locally – thesea are  probably descended from birds released by some non-thinking idiot who decided it would be cool to release doves symbolizing something or other at a ceremony somewhere near here.  Anyway, said skyrats appeared about four years ago, and have been doing well here.

Eurasian Collared Dove

Periodically, though, a truly native sky shark comes by to thin the herd a bit, and that is what happened yesterday.   It was great entertainment to watch the falcon, though I doubt the doves thought so. 🙂  I saw him miss his target by inches on one pass; the dove was surprisingly agile in the air when the situation warranted!   The falcon was around for a while, and then vanished.   I hope he finally got dinner and settled down near by to enjoy his repast.

Almost exactly a year ago, we had a similar opportunity to watch a goshawk for a few days, and the second picture, below, shows the final outcome.  The first picture was taken a few days before the second one, and it appeared to be the same animal.  In the second image, the hawk is standing over his plucked prey that he has been eating.

Sharp-shinned Hawk in the poplar outside my office window.

Sharp-Shinned Hawk and Dinner

It was an amazing show.

Of such events, are the sciences of behavioral biology, or ethology, and ecology, made.  And people who study these things in terrestrial environments truly lose out.  I used to tell my students that one of the very neat things about being an ecologist who worked subtidally using SCUBA was that one got to see a lot more interactions than one’s terresterially-bound counterparts.

If you think about it, how many times have you seen a predatory animal in nature around you (excluding those events caused by humanity or human pets ) actually kill and eat a prey organism?  I would wager that the total sum of those events witnessed by anybody is pretty small; I know it is with me, and I look for them.  It is possible to calculate some sort estimat of the odds of seeing such an interaction at any given moment.  For example, if a person is 35 years old, that person has been alive about 1 billion seconds.  If each second is a discrete a moment of observation, the rough, back-of-the-envelope odds of having seen such an event through that person’s lifetime are easy to work out.  First, assume that about of the third of the time has been spent sleeping, so subtract a third of the billion away, phffftt!, and now there 667,000,000 million potential moments of observations.  Then assume that for the first third of the persons’s life she or he was effectively unaware of the world (childhood, teen-aged years, and so forth), so subtract a third of the previous remains and now there about 444,700,000 million potential observational moments.  Now, drop out a another third for meals, and other daily mindless activities, and now there about 296,400,000 million observational times.  Being generous, let’s say our victim subject was outside observing nature 1/10 of each day (and I think that will be a vast over estimate for most folks, but, what the hey, let’s go with it), so now there are 29,640,000 potential moments of observation.  And if that person witnessed 10 natural events wherein one animal killed and ate another (and I suspect that would an overestimate), that means our subject’s odds of seeing such an event were 10 in 29,640,000, or 1/2,964,000, or (very roughly) 0.0000003.

Pretty slim odds (!) of seeing some interesting natural event such as predation.

Back to my point about working underwater in the marine world, I could see animals kill and eat other animals many times during a hour’s dive, and often did so.   Below are a couple of images  recording some of those times (and be sure to click on the sculpin image to see the shrimp’s antenna).   Obviously, the moral of the story, of course, is that one must dive to really observe and understand nature.

A Buffalo Sculpin, Enophrys bison, that has just eaten a shrimp, note the antenna visible protruding from the mouth.

A red rock crab, Cancer productus, eating a scallop.

Yeah, sure!!!

But the point that visible large animal to animal interactions are more evident in the marine environment is, I think, a valid one.

Behavior and Marine Aquariums

Thinking about the point made above, and making a not-so-tortuous connection to marine aquaria, those boxes of water full of critters may be (depending, of course, on how the boxes are set up, and what’s in them) quite reasonable analogues to a natural environment.  And that means, any aquarist with such a tank should expect to see predatory (and other “natural” ecological or behavioral) events occurring with some reasonable frequency in their systems.

And, of course, all of us aquarists (or at least of us who observe our systems) do see these events.  Everytime we feed some live animal to our livestock, we see predation, albeit those are staged events, but with suspension-feeding animals, corals for example, within the staged event, the actual feeding behavior on the part of the coral, is likely essentially the same as when the “real thing” occurs in nature.  But even if those “wo/man-made” events are factored out, all aquarists have seen unintened predation occur in our systems, and sometimes rather frequently, as when when a newly-observed acoel flatworm on the aquarium wall is seen to capture and eat a copepod.  In fact, by observing some of these types of events any aquarist worth their artificial (sea)-salt can – for some animals, at least – see interactions that have never been seen in nature, and depending on the interaction – such as with the flatworm and copepod example – such events may be exactly what occurs in the real world, or a mimic so close that the difference is immaterial.

So, folks, on this cold winter, while the snow outside blankets the northern hemisphere, those of you with coral reef aquaria kick back and relax and enjoy the tropical world in your living room.

It’s a world of your making and if you have done your job, properly, it is a VERY real world.

For the rest of you, it is time to shovel snow!

Until later,


Angels of Death

Wednesday, December 15th, 2010

Hi Folks,

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.”

Until later,