Posts Tagged ‘mollusca’

Benthic Natural History In Cowlitz Bay, Waldron Island.

Monday, February 4th, 2013

Passing into deeper water from the eelgrass beds found in the shallow nearshore environments of many embayments of the American San Juan Islands, the highly organic muddy sand substrate is typically replaced by a less organic or “cleaner” mixture of sand and silt.  Such a transition is certainly the case in Cowlitz Bay of Waldron Island.  I can verify that the silty-sand substrate continues to, at least, a depth of 50 m (165 feet).   Except for emergent rocky outcrops, this habitat type is likely characteristic of all the deeper water of Cowlitz Bay and the nearby San Juan Channel and Boundary Passages.

The tidal ranges that distinguish this region, coupled with its geography, mean that high tidal currents are the norm, and the volume of tidal water movement is immense.  All of this, added to the dense, rich plankton found in those waters creates a habitat that is probably nearly optimal for suspension feeders.  As a result, virtually all of the hard subtidal real estate is occupied some sort of organism specialized to grab food or nutrients from the water moving past them.  Subtidal rocky substrates are often characterized by dense populations of suspension-feeding epifaunal sea cucumbers.  And, although it may seem unlikely, some of the unconsolidated, silty-sand, habitats are also dominated by dendrochirote holothurians, albeit in this case these cases they are infaunal, not epifaunal.  Infaunal sea cucumbers dominate the subtidal Cowlitz Bay benthic environment below 10 m.    

0 - Pentamera cf populifera 11vii77 6m Cowlitz Bay, Waldron Id. 01 Juveniles

Pentamera individuals extending from the bottom of Cowlitz Bay, 11 July, 1977.  The abundance of the adult animals exceeds 20,000/m2 (about 0.2 m2) is visible.

Pentamera sp. indivdiual with some of the many juveniles in the sediment circled.  Taken 11 July, 1977.

Pentamera sp. adult indivdiual with some of the many juveniles in the sediment circled. Taken 11 July, 1977.  The juveniles become evident in the sediments in early summer, indicating spawning likely occurs in the spring.

Although a few other species are rarely found, the vast majority of these suspension-feeding, infaunal cukes belong to a few species of Pentamera.  The individuals belonging to the different species are relatively similar in size, shape, and coloration making them effectively indistinguishable in the field by non-specialists, so I will refer to them all as Pentamera.  Living buried in the sediments they feed by extending a small portion of the oral end of the body above the sediments.  This exposes just a bit of the animal, primarily the mouth, and its surrounding crown of highly-branched feeding tentacles.   

White, and only about 2 or 3 cm long, these relatively small sea cucumbers are often found in beds so very dense that in the summer, the benthic sediment appears snow-covered due to the many tentacles visible.  In the clear water of the late autumn and winter plankton-free periods, these holothuroids do not feed.  Presumably quiescent, they remain buried under the sediment surface.  During these seasons, the habitat looks relatively barren; with only scattered larger animals, such as individuals of tube anemones, Pachycerianthus fimbriatus, orange sea pens, Ptilosarcus gurneyi, snake-skin stars, Luidia foliolata, sunflower stars, Pycnopodia helianthoides, or weather-vane scallops, Patinopecten caurinus being evident to the casual observer. 

Patinopecten caurinus, the Weather Vane Scallop, about 15 cm (6" in) in diameter. Photographed in the Summer (June, 1977).  Note the visible Pentamera cukes.

Patinopecten caurinus, the Weather Vane Scallop, about 15 cm (6″ in) in diameter. Photographed in the Summer (June, 1977) on the benthic subtrate of Cowlitz Bay; note the abundant Pentamera cukes.

Patinopecten caurinus.  Area as before, except it was photographed in the ealry winter (December, 1976).  Note the lack of visible cukes.

Patinopecten caurinus. Area as before, except it was photographed in the ealry winter (December, 1976). Note the lack of visible cukes.

With beginning of the diatom bloom starting in February, smaller life “returns to”, or more correctly, becomes evident again on the benthos.  The sediment becomes covered completely with a thick and rather ugly, dense dark brown film, consisting of several species of microalgae, primarily diatoms and dinoflagellates. 

Unidentified Polyclad Turbellarian, photographed in April, 1983.  The "black material" is the diatom film that is found in this area in the spring.

Unidentified Polyclad Turbellarian, anterior end to the left, photographed on April, 1983 on the substrate in Cowlitz Bay.  The “black material” is the diatom film that is found in this area in the spring.

By early March, many turbellarian flatworms of several visually distinctive types are commonly found gliding over the brown algal film and sediments.  These small worms, each only a few millimeters long, may be distinguished by their differing shapes and color patterns.  Although common, at least in the spring, virtually nothing is known of their natural history.  Shortly after the worms become common, small caprellid amphipods, otherwise known as “skeleton shrimp”, seem to appear out of nowhere and are soon found covering the diatom film.  These small, about a centimeter (0.4 inch) long, animals reproduce rapidly and soon reach abundances around 1 animal per square centimeter, or a density of 10,000 animals per square meter.  As they become common, pelagic predators, such as ctenophores and chaetognaths, may be observed grabbing copepods off the bottom and swimming back up into the overlying water.

A Sagitta (planktonic chaetognath carnivore) photograph near the bottom, hunting for caprellids.

A Sagitta (an almost completely transparent planktonic chaetognath and a predator normally on zooplankton) photographed near the bottom, where I have seen other individuals grab caprellids.

 By the middle of March, the spring plankton are in full bloom and the Pentamera are beginning to feed.  By moving up and down in the sediment, the resulting bioturbation soon destroys the diatom film, and the sediment becomes relatively clean again.  Snake-skin stars, Luidia foliolata, are common in this habitat where these sea cucumbers are their principal prey.  Caprellid amphipods, Caprella gracilior, and small hermit crabs are often seen on the aboral surface of the stars.  The Luidia-sized, star‑shaped, feeding depressions, along with the small piles of regurgitated remains attest to the star’s feeding habits.  Pycnopodia helianthoides is also commonly found in these beds and may also feed on the sea cucumbers.  Some aspects of the natural history of Luidia in this habitat will be discussed in subsequent post.

 Individuals of the large, up to 15 cm (6 inches) in diameter, weathervane scallops, Patinopecten caurinus, rather rare elsewhere in the San Juans, are found not uncommonly in these cucumber beds.  They are found lying in shallow, somewhat bowl-shaped, depressions probably created over time by the scallops’ feeding currents which might gently displace and excavate the sediments.  Eaten by the sunflower star, the scallops will swim in response to being touched by the predator.  They are not particularly vigorous swimmers, however, nor do they seem to start swimming immediately, thus they could be captured relatively easily.  Their shells are a common feature in this habitat, so presumably some predators are capturing them.  These large shells, either living or dead, provide about the only hard substrate in these habitats, and are often covered with barnacles, algae, or occasionally attached bryozoans or hydroids. 

Maroon more pachycerianthis

Both color varieties or “morphs” of  Pachycerianthus fimbriatus found in the benthos of Cowlitz Bay.

The tube-dwelling anemone, Pachycerianthus fimbriatus, is particularly common in this habitat, and becomes very abundant just below the dense Pentamera beds in the more silty habitats of the steeply sloping areas.  Pachycerianthus individuals may be colored either gray or a dark brown to maroon.  These do not appear to represent separate species, and the different colors have no known significance.  Close examination of the anemones will show some very small epifaunal, possibly stenothoid, amphipods visible as small dots moving over the anemone’s body and tentacles.  During the spring and early summer periods of dense plankton, it is possible to watch the Pachycerianthus catch copepods, and other small crustacean zooplankton, with their long tapering, thin, tentacles. 

An ectoparasitic or commensal stenothoid amphipod on a Pachycerianthus tentacle.  Assuming the tentacles are about the same size (and they are) compare this amphipod to the hyperiid amphipod captured as food by a different tube anemone (next illustration).

An ectoparasitic, or commensal, stenothoid amphipod on a Pachycerianthus tentacle.  Assuming the tentacles are about the same size (and they are) compare this amphipod’s size to that of the hyperiid amphipod captured as food by a different tube anemone (next illustration).

A small Pachycerianthus fimbriatus with a captured planktonic hyperiid amphipod (arrow).

A small Pachycerianthus fimbriatus with a captured planktonic hyperiid amphipod (arrow).

 These slightly deeper habitats where Pachycerianthus is most common, ranging downward from about 10m (33 feet) in depth, have a silty sand substrate.  Pentamera are found in these regions, they are just not as abundant as they are in the dense assemblages in shallower water.  Individuals of the orange sea pen, Ptilosarcus gurneyi, are well represented in these deeper habitats, and although they are not as abundant here as they are in the dense sea pen beds of the lower Puget Sound region, they are nonetheless found relatively frequently.  Occasionally, a different type of pennatulacean, a sea whip, may be found.  In the genus Virgularia, these whips are narrow pennatulaceans, with short “leaves”.   At least two species within this genus found in our waters and they are not terribly difficult to distinguish in the field.  The species found in Cowlitz bay is small, tan to whitish, with small “leaves” and is seldom over 15 cm (6 inches) in height.  The feeding zooids often appear to arise from directly from the central stalk.   The other species, found in other areas, such as Lopez Sound, is larger and more robust, pink to orange, and often reaches heights of 50 or more centimeters.  This species has larger relatively distinct “leaves” with the gastrozooids on them. 

A small, about 8 cm (3.5 in) high, pennatulacean, probably a species of Virgularia.

A small, about 8 cm (3.5 in) high, pennatulacean, probably a species of Virgularia.

 Several nudibranch species are also found in these areas, most of which are probably preying on the cnidarians.  The largest and most evident of these are individuals of Dendronotus iris.  These are amongst the largest local snails; in this area they often reach lengths exceeding 25 cm (10 inches) which is probably due to the high abundances of their preferred prey, the Pachycerianthus anemones.  They approach the anemones by slowly crawling under the tentacle crown, to where the anemones extend from their tube.  They, then, reach up rapidly, bite, and hang on to either a mass of tentacles or even the anemone’s column.  Generally, the Pachycerianthus rapidly withdraws into its tube when it is bitten, and in these cases, it often pulls the predator in with it.  Sometime later, the Dendronotus iris often crawls out of the now empty tube, and may set off in search of another anemone.  The nudibranch may, at times, lay its loosely coiled egg masses attached to the Pachycerianthus tube, bits of shell, or just bits of the sediment.

0 - Dendronotus iris Cowlitz Bay, Waldron Id. -7m 11vii77 WA 01

A 10 cm (4 inch) long Dendronotus iris in Cowlitz Bay. Photographed at a depth about 7 m. This large nudibranch reaches over 30 cm (12 inches) in length, and eats Pachycerianthus. 

Other nudibranch specimens are found in the area, and they can be relatively common at certain times of the year.  Dendronotus albus specimens will be found occasionally, preying on those few hydroids that are found attached to the shell fragments or other hard substrata present on the sediment surface.  These nudibranchs are slender and may reach lengths of about 10 cm.  The basic ground color is white, but the tips of the branched cerata are tipped in orange.  Individuals of another dendronotid, Dendronotus albopunctatus, are often abundant in the spring.  These animals are brown to pink and freckled with small light dots.  They only reaches lengths of 2 to 3 cm (up to about 1.5 inches), but they are recognizable by their somewhat “oversized”, relatively large, “front” cerata, which are often about a centimeter in length.  Little is known of the natural history of this species, although it is likely a predator on small cnidarians.

Dendronotus albus.

Dendronotus albus is a not uncommon, small, about 3 cm, (1.2 inches) long, nudibranch in habitats such as those found in Cowlitz Bay.  It eats hydroids, as this individual was doing when photographed

0 - Dendronotus albopunctatus Cowlitz Bay, Waldron Id. -9m 28iv83 WA 01

Dendronotus albopunctatus, about 3 cm (1.2 inches) long on the sediment of Cowlitz Bay.  It also has been seen to eat hydroids.

0 - Acanthodoris brunnea, Cowlitz Bay, Waldron Id.,  -9m, 13v86  WA 01

Acanthodoris brunnea, about 2 cm (0.8 inch) long, photographed on the sediment of Cowlitz Bay.  Reported to eat bryozoans, this dorid species is found on muddy-sand, a habitat notably lacking in bryozoans.  In this region and habitat, it is likely eating something other than bryozans.

Acanthodoris brunnea is another nudibranch species that is somewhat common at times in this habitat; little is known of its natural history.  These animals are small dorids, roughly the same size as Dentdronotus albopunctatus, reaching lengths of 2 to 3 cm (up to about 1.5 inches).  Their basic coloration is brown; the individuals are covered with distinctive relatively large papillae on the back.   This species is considered to be predatory on bryozoans, but that is unlikely in this region as bryozoans are exceedingly rare in this habitat.

Also found in these areas are pennatulid-eating nudibranchs in the genus Tritonia.  The most abundant of these are individuals of the small white Tritonia festiva, described in the earlier post on sea pen beds.  Here, as well, T. festiva individuals seem to prey on Ptilosarcus.  Individuals of the larger, orange nudibranch, Tritonia diomedea, are also occasionally seen in these areas.  They seem to prefer the larger Virgularia as prey.  

Large shelled gastropods are relatively rare in this particular habitat, although several smaller species can be very abundant.  Perhaps the largest commonly found gastropod, and certainly one of the most beautiful, is the wentletrap,  Epitonium indianorum.  These animals are often found buried near to the bases of the tube anemones upon which they feed.  As with most snails, wentletraps have a feeding organ called a radula; unlike the “classic” gastropodan radula which functions something like a rasp, filing off pieces of tissue, the wentletraps’ radulae are highly modified and look like an inverted thimble lined on the inside with sharp teeth.   A wentletrap crawls up to the anemone and pokes the anemone with its radula everting the “thimble” in the process.  This turns the radula inside out, which in turn, carves a circular hole in the tissues on the side of the anemone.   The lacerated tissues are eaten, and the snail extends its proboscis which has the radula on its tip through the hole and proceeds to use the radula to cut up and eat other internal anemone tissues.  These snails reach lengths of 3 cm or more, and don’t seem to move much once they have found an anemone to feed on.  It is recognized by the distinct axial ribs, the rounded aperture, and the relatively high spire.

 One cephalopod can be relatively common in the lower slope areas, the Pacific Bob‑Tailed Squid, Rossia pacifica.  This small benthic squid lives buried in the bottom during the day.  If a diver is careful, they can sometimes see the slight depression that the Rossia occupies, and then can make out the eyes watching him.  The hole for the siphon is generally visible and if approached carefully, one can see the regular breathing movements of the mantle.  Rossia pacifica reaches lengths of about 10 cm, and seems to live about a year or eighteen months.  They have an interesting, stereotyped, escape response which I have described, briefly, in a previous post.  This small squid preys on small shrimps, crabs, and fishes, and is a nocturnal hunter.

Well, that’s enough for now… :-)

More later,

Cheers, Ron

 

 

 

 

 

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,

References:

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,

Cheers!!!

More Scaphopod Information – Including Some Ancient Scaphopod Jewelry

Friday, August 26th, 2011

 Scaphopod Connections

Over the past few days, I have finished scanning my images of Native American scaphopod jewelry and decorated clothing, all of which were photographed in 1987 in the Burke Museum on the University of Washington campus in Seattle.  Some of the Native American dentalium jewelry/clothing images that I have are REALLY impressive, not only for the wealth they contained, but also for the tremendous skill of the remarkable women who made them.  Somehow, I wish I could find something like the shawl in the image below in an old trunk in my garage, and take it to the appraisers on The Antiques Roadshow.  It would get the attention it really deserved.  Ah… well.  All I am likely to find in old trunks in my garage is old trash covered in old dust.

 A shawl, made by a seamstress and master craftswomen from one of the Plains Tribes, in the mid-to-late 19th century.

This is a shoulder wrap or some sort of vestment, I neglected to photograph both sides in 1987, when I took the image.  I would estimate that there may be close to a 1000 Antalis pretiosum shells in this item.

Not surprisingly considering their shapes and durability,  scaphopod shells were widely used in ornamentation elsewhere and elsewhen throughout history.   The following image was taken by Don Hitchcock in from the Dolní Věstonice Museum in the Czech Republic, which has some wonderful artifacts recoverd from an ice age mammoth hunter’s site.  

dolniimg_2014b

A reconstructed necklace made from fossilized Dentalium badense shell fragment artifacts recovered at the Dolní Věstonice site in the Czech Republic.  The artifacts at this site have been dated with Carbon-14 to about 29,000 years ago.  Photo: Don Hitchcock donsmaps.com

In one of the more bizarre coincidences I have had recently, I found the above image and information with the assistance of Mr. Google and associates.  I hadn’t seen it prior to findinig on the web, but I knew that there should be ancient European, Asian or African dentalium work illustrated somewhere on the web, and charged ahead to find something I might use.  I found this image, and it fit the bill of what I wanted, and I went to track down some information about it, including where the Dolní Věstonice site (which, from reading the information at the site, I realized I must have read about it sometime ago, I recollected nothing at all about it ) is located. 

This Google Earth image shows where the Dolní Věstonice site is located.  The other site indicated, the Frydek-Mistek region, is  where my ancestors, at least back to before the mid-1700’s, lived. !!!  My great-great-grandfather was one of four brothers that migrated together from this area to the US (Texas) just after the Civil War.

Nobody knows, of course, what happened to the descendents of the people who made and used the scaphopod shell necklace, or even if they left descendents at all.   But I think it could be possible -stretching possibilities very thinly- if those descendents remained in that area, that maybe some of the genes of the person who made the scaphopod necklace may have decended to be in the genome – some 28,000 years later – that directed the growth of my scaphopod-studying body.

In closing this entry, I must thank Don Hitchcock for his gracious permission to use his fine image of the scaphopod necklace.  Don has an immense array of web information about the paleolithic period throughout the world, and I have linked to his site in my blogroll.  It is well worth a visit.

Until later,

Cheers,

Scaphopods

Thursday, August 18th, 2011

Where

Recently I started scanning my images of scaphopods, an animal group from which very few people have seen living animals.  I did a lot of research on them actually starting about 1975, and becoming intensely active in 1983 and finally winding down about 1997.  I still have a paper or two to write but I haven’t done any field work in a long time.  I described two deep-sea species (1, 2) from specimens sent to me, but most of my work has been done on the scaphopods found in the shallow waters of the Northeastern Pacific.  Scaphopods are particularly common in many of the fjord environments north of the Strait of Juan de Fuca.  I spent some small amount of time examining their distribution in the waters of Northern Puget Sound, particularly in the northern American San Juan Islands.  In this area, two species of scaphopods, Rhabdus rectius and Pulsellum salishorum are found, and may be reasonably common in a few areas.   There a couple of marine research laboratories/field stations in that region, but as far as I know, I am the only person in the last half century who has worked at one of those labs and done any kind of research on scaphopods.

During the period from 1981 until 2003, I taught at various times at a Canadian marine station located in Bamfield, British Columbia, situated on a small inlet on the southeast side of Barkley Sound, a large fjord system on the west side of Vancouver Island.  This marine laboratory, known as the Bamfield Marine Station from its beginning in the 1970s until it morphed into the Bamfield Marine Sciences Centre in the early 2003, offers easy access to some of the scaphopod habitats of the Barkley Sound region.  For the two-year period from September of 1983 until September of 1985, I was the Assistant Director of the marine station, and actively carried out an intensive project on scaphopod ecology and natural history.  Subsequent to that time, I worked up data collected during that period, as well as initiating other scaphopod work, mostly with specimens sent to me by various researchers.   As a result, I have published about a half dozen research papers on scaphopods, and have a couple of more in the works… if I can only get my act together enough to finish them.

The Critters

Scaphopods, or “tusk” or “tooth” shells are mollusks that live as subsurface predators in the marine sandy or muddy sea bottom.  Covering an estimated 60% of the planetary surface, this is THE largest habitat in on the planet’s surface.  As the scaphopods are either abundant or dominant predators in this habitat, that makes them some of the most ecologically important animals. 

By last count there are about 8 to 10 people living today who have published papers on scaphopods, which may make them the most understudied of all important marine animals.  Given that a number of those people are museum workers whose entire conception of the Molluscan Class Scaphopoda is that it is a collection of oddly shaped shells, it is evident that the world-wide scientific interest in the group is probably so close to nil as to be statistically indistinguishable from it.

This means that to a very real extent, that anybody who works on scaphopods as a full, or even part-, time venture is on their way to committing, or has committed, scientific/academic suicide.  While it is true, to paraphrase one of my old profs, “If only five people work on your group, you can’t be ranked any lower than the fifth most prestigious worker on the group.” 

However, if only five people work on your group of interest, it means nobody will care what you write.  So, the good side is that everybody working on the group knows who you are. On the other hand, nobody else in the world – or known universe – cares who you are or anything about the animals…  If there is so little interest in group worldwide, no matter how good your publications are, they will simply disappear into the large black cesspool of unread papers as nobody will care about you write.  

Well, who am I to argue?  I will state, however, in my defense, after that statement that I am the senior author of the definitive reference about the animals published to date:  Shimek, R. L., and G. Steiner.  1997.  Scaphopoda.  In:  Harrison F., and A. J. Kohn, Eds. Mollusca IIMicroscopic Anatomy of the Invertebrates. Volume 6B: 719-781.  Wiley-Liss Inc. New York, NY.  ISBN 0-471-15441-5.   Whooopty-doooo…

 

Five species of Scaphopods found in the Barkley Sound region of Vancouver Island, British Columbia, Canada.  The scale bar is in millimeter.

From top to bottom, Pulsellum salishorum, upper two rows, females on the left, males on the right, next single row, Cadulus tolmiei, female left, male right, below that species is a single row of two Gadila aberrans, female left, males right, The next two individuals are Rhabdus rectius, female on the top, male on the bottom, and the lower-most individual is a single specimen of Antalis pretiosum (formerly Dentalium pretiosum), the “Indian Money Shell.”  These individuals were alive at the time, and in the high definition of the moment, the top four species have shells that are thin enough to be translucent, and the gonads from each gender are differently colored, so I could discrimate the sexes.  It is hard to see in the low res image here, but if you look at the top animals on the left, you can see a hint of pink in the shell, and that is the color of the ovaries of Pulsellum salishorum.

Heretofore…

Scaphopods were very economically important animals in the North American native cultures.  Given the common name of the “Indian Money Shell,” one species, at one time called “Dentalium pretiosum,” was collected and traded throughout large parts of Northern North America.  Here is an image from a National Geographic Magazine article about the trade; I was a technical advisor to the NGM for that article.  The scaphopods were harvested in by some of the tribes from the Pacific Northwest, both in what would become Canada and the U.S.  There are numerous “tales” about how the shells were collected, and at least two different and likely ways of collecting them.  Knowing what I found out about the habits of that species (now called Antalis pretiosum), it appears that very few of the actual living animals were collected, but rather shells containing small hermit crabs the primary source of “scaphopods.”  There is a hermit crab in the region were the scaphopods are found that is not coiled to fit into a snail shell as are most hermit crabs, rather this one, Orthopagurus mimumus, has a straight body and lives preferentially in the large “dentalium” shells.  The crabs crawl around on the surface of the habitat, while the living animals are generally deeply under the surface, at least a foot (30 cm) below the water/sediment interface.  In fact, the living scaphopods all have a rapid burrowing response – an exposed scaph is a dead scaph – as crabs and fish eat them.  In text books and references, they are often illustrated as having their pointed ends exposed from the sediments, and some are found this way,  between1 in 60, to 1 in about 10,000 depending on the species I have looked are exposed at any one time.   So much for the standard references…  More about why this should be so in my next issue of this blog.

Anyway, one of the more recent “proofs” of the hypothesis that it was mostly dead scaphopod shells inhabitated by hermit crabs that were collected actually comes from one of the National Geographic Magazine sites.  They have a series of images purported to be Antalis pretiosum, all of dead scaphopod shells taken by David Doubilet, and  all showing hermit crabs showing hermit crabs in the shells.  Doubilet was apparently in search of the wily dentalium and, by golly, he got some pictures of it… or at least of its shell.   Interestingly enough, there is an image also on their site showing Antalis pretiosum feeding below the sediment surface.  This wonderful image is a painting by Gregory A. Harlin, and it clearly shows that scaphopods don’t have legs…  Of course, Doubilet didn’t look at the painted image.   One further note that adds even more humor to this bit of fubardom (fubar = fucked up beyond all recognition) is that Harlin’s painting was done for the previously mentioned earlier article in NGM about the dentalium trade for which I was a technical advisor.  Harlin based his painting on my drawing of Rhabdus rectius feeding below the sediment surface that was used in Shimek and Steiner, 1997. 

A diagram of Rhabdus rectius shown in its feeding posture below the sediment surface, drawn in life from animals in aquaria. Compare with the painting by Gregory A. Harlin,

The dentalium shells collected on the coast were traded through out North America, at least as far east as the Great Lakes and were quite valuable.  They were used in the construction of jewelry and as ornamentation on clothing.  I have read, with no real estimate of the validity of the statement, that one or two of them could be exchanged for a tanned buffalo hide.  Consider that when you look at the image I have imbedded below.

 

Plains Indian neck ring jewelry in the collection of the Burke Museum,University of Washington, Seattle, Washington.

It has been reported, that given that the shells of the animals were quite valuable, it stands to reason that the one of the first things the Europeans did (in the guise of the Hudson’s Bay Company) was to “devalue the currency” by flooding the market with “counterfeit” shells.  When the HBC traders began to realize how valuable the shells were, they sent word back up the communications chain, and European shells were harvested in some relatively great numbers.  The European species, Dentalium entale, is/was essentially identical to Dentalium pretiosum and easily collected (and remember, both are now in the genus Antalis).  These were sent to HBC traders throughoutNorth America and used to purchase all sorts of trade goods.  So many shells became available that this sufficiently brought the value of the shells down so low as to make them worthless as trade goods for the coastal tribes as they could not harvest enough to get the traditional materials (such as buffalo robes, and they became dependent upon the HBC to sell them blankets).  If this is true, it is a great (?) lesson in market economics…

More on scaphs later….

Until then…

Cheers, Ron

 

Identifications…

Tuesday, January 11th, 2011
Ah… well, yesterday I started to do some research on an article which may have the title of  ” The Vampires of the Sea.”  A twilight  article dealing with…

those bloodsuckers, bar none – Pyramidellid snails.   

Whether or not I develop this article fully depends on a lot of things, not the least of which the direction my muse (and I do have one – a characteristic I find “amusing”…  :-) ), takes me.  And also, of course, whether or not, I can find an editor who will accept it.  Anyway I am still in the very early stages of this thing, and I am trying to find some more background information about Pyrams. 

Now, like Yogi, I figure I am a bit “better than the average bear” with my knowledge of the group, but I really need to know more before I do anything that can be considered to be a reasonable and – hopefully – entertaining article about them.

Basically, the Gastropod family Pyramidellidae is a very large group of small… white… snails without any really nice identifying characteristics.  There are, quite literally, thousands of names applied to these snails, and how those names relate to the actual species – if any – of those snails is really open to question.  As with many marine groups – probably as with MOST marine groups – of animals, they are a taxonomic mess.  There are three basic reasons for this, the primary one is that they are all – dare I say it, again – small,  white, and feature-less snails.  If you think about it, once you have the basic constraints of a small, helically-coiled, shell, there are NOT a lot of ways that those constraints can be varied.   In point of fact, back in the 1960s, a paleontologist named David Raup, wrote a series of nice papers noting that virtually all marine animals with a “shell” can be easily described mathematically (Raup, 1962; 1966; 1969). 

The term “shell” in this sense is restrictive and excludes arthropods – even though they are “shellfish” they don’t have a “shell” in the way that Raup meant: “a non-living external covering to the animal.”  What arthropods have is an “integument” – a covering that is made of an intricate and complex fusion of living and secreted elements that is an integral part of the animal’s body, interiorally and exteriorly.  If you try to remove a shrimp’s “shell,” you are left with a mass of dead flesh.  If you try to remove a snail’s or a clam’s shell, you will find that, in many cases, it is quite possible to do this and still have a living animal.  And that animal may remain alive – in the case of some snails – indefinitely.  Clams without a shell perish in short order, as they can’t feed.  But snails without a shell can generally do everything shelled animals can do.   Everything, that is, except withstand the bite of a predator’s jaws.  Virtually every biologist who studies large populations of marine snails occasionally finds a shell-less one; probably an animal whose shell was eroded away by a sponge, or whose shell was cracked by a crab and, by a miracle, the shell was removed.  As an example, over the course of three years, I encountered two almost-naked specimens in one species, Ophiodermella inermis, that I worked on many years ago.

Ophiodermella inermis, photographed in Dyes Inlet, Washington.

Anyway… Raup found that virtually all mollusk and brachiopod shells were basically helical in shape, and that all fundamental shell shapes could be described by only three parameters, 1) the shape of the shell’s aperture, 2) the rate at which the shell’s aperature coiled around the central axis, giving the width of the animal, and 3) the rate at which the coiling moved along the central axis which determines the animal’s length.  As all of the functions occur simultaneously, how each of the parameters varies in relationship to the others changes both the absolute and relative proportions of the shell’s shape.

This diagram below shows how the shell parameters determine the difference in shell shapes for some snails commonly found in marine reef aquariums. The top shows a Nerite; here the shell aperture just moves in a spiral around the axis of coiling and moves outward at a rate that is not very large.  This results in a spirally-coiled shell where the whorls appear to overlap.  The other shells are trochoideans.  And here the parameter of “aperture shape” is circular.  The aperture moves around the axis of coiling at various rates – giving a turbinate or trochoid shape.  Additionally, the aperture moves along the axis of coiling determining whether the shell is squat or elongate.  Although the flat Stomatella seems to be very different from a conical Trochus in structure, with a little thought, it is easily possible to see how those shell shapes are related.

.Shell parameters illustrated by various snail shells; all shells grow in three dimensions but the position of the aperture in each successive whorl may change due to only 3 parameters. A. Growth of a shell where the aperture shape moves in a spiral within one plane; the nerite shell is an example of this. B. Here the aperture moves along the axis of coiling but remains tangent to that axis; the illustrated turbinid is an example of that growth. C. Here the aperture moves along the axis of coiling, but also translates or moves outward from that central axis. An opening called an umbilicus in the center of the shell is the result. The illustrated trochid shows this growth form, with the earlier positions of the growth generating aperture shown in gray. The shell of Stomatella is auriform, an extreme example of the prominence of the whorl translation rate.

Given that all molluscan shells can be basically described in this manner, if shells lack much distinctive coloring, sculturing, or extra ornamentation, it should be apparent that there really are not a lot discrete characteristics that can be used to uniqually differentiate any given shell from all others that are basically similar in shape.

That lack of potential characters is the first factor that has caused taxonomic problems with pyramidellid shells.

The second and third problems were two malacologists, William Healey Dall and Paul Bartsch.  Dall was the first curator of mollusks at the United States National Museum (aka the Smithsonian Institution).  Bartsch was his “disciple” and successor.  As curators at the Smithsonian, a lot (really A LOT!!!) of specimens (= dead shells) were sent to them by various collectors.  As they tried to identify these shells, they often found that the shells were not “quite” like shells in the museum’s collection – or in other museums’ collections.  This meant that these shells were then new to science and needed to be taxonomically, or scientifically, described.  Virtually all animals that are described from United States regions or by American authors have representative or “type” specimens deposited in the Smithsonian’s collections, so they had a lot of comparative material.  Presently, that is a huge number of specimens, several millions.  Back in Dall’s time, the collections were a lot smaller… but still relatively very large…  So, they had a lot of material with which to compare any given specimen in their descriptions.  Thus, if they decided a given specimen was a “new” species the odds would seem to favor the fact that it was new. 

Maybe…

Typically what these two ol’ boys did, was to let specimens accumulate until they had enough to write a short (or sometimes very LONG paper describing them all).  At the time, the custom was to describe a molluscan species on the basis of one shell. 

ONE

THE

TYPE.

The type was supposedly an “average” or representative shell that “typified” the species.  By the way, Dall and Bartsch were by no means alone in the way in which they described “their” species.  It was the standard method of the era.  They were, however, especially prolific, and it seems, especially “gifted” with the inability to find unique precise and useful descriptive terms.  Simply put, many of their descriptions are “precisely ambiguous,” they are written in ways that seem to precisely describe the specimen, but which don’t allow a reader to determine if a given questionable shell that they are holding in their hand is from that unique species.  I think this was because they didn’t include much or any information addressing variations between specimens of the same species.

And what about those variations?  Well, Dall, at least paid lip service to the concept of variation, but he generally didn’t include any useful way to describe variations in the species he described.  Any good field biologist knows that variation is quite literally “the stuff of life.”  For example, for little white snails, such as pyrams, if one collects one hundred specimens from a known species, they will vary in length, width, the number of whorls, slight color variations occur, the proportion of length to width will vary a bit, the number of ribs on whorl may vary, and on and on and on…  One specimen really can’t do it.

Nonetheless, the conception of a species at the time, which was reinforced by rules of Linnaean taxonomy implied that there was no variation in a species.  This was a result of considering all species to be divinely created.  If a creator designed each species, he/she/it/they would obviously get it right the first time and there could be no variation.  That was all fine and dandy up until the publication of The Origin of Species in 1859.  Once the concept of evolution became established, the concept of a species HAD to include variation.  And so it did.

In concept.

But in practice…  Well, let’s just say the idea of variability in a species was not an easy one to get across.  Modern descriptive statistics is just that, modern, so at that time there was no formal way to estimate variability.  The concept of a standard deviation wasn’t there.  Even including a range of sizes in a species description was rarely done.

In essence, for any species – the idea of that species was “crystalized” within a single typical specimen, the type.

Over his lifetime, Dall described 5,302 species in every group of animals defined at the time, from mammals to mollusks.  Most, however, were snails.  Bartsch described an additional 905.  The heyday of these descriptions extended from the 1870s through about 1925 for Dall (several years after he died, actually, as Bartsch published some of Dall’s descriptions after his death).  Bartsch retired in 1945 and died in 1960, and I think his last taxonomic publications were in the 1950s.

Modern day molluscan taxonomists who work in the Pacific where these men had the largest taxonomic effect have a love-hate relationship with them.

Love…about 0.000001%,  Hate… well, do the subtraction.

Simply put, it is essentially impossible to differentiate most small snail species described by these men.  They gave lip service to the concept of species variability, but using the typological approach and their writing style such variability was impossible to descibe.  Interestingly enough, that is not the case with many other prolific describers of molluscan species that were writing at the same time.  Henry Pilsbry was another malacologist who described a lot of species; according to his article in Wikipedia, he wrote over 3,000 scientific papers and described over 5,000 species.  His descriptions have stood the test of time well, so the problems with Dall and Bartsch were due to Dall and Bartsch.

How bad is the situation, really? 

Pretty bad.   Really!

For example, if a large collection of pyramidellids or other small snails is taken from one bay or locality, their parameters will vary, of course.  If those specimens can be determined by other means (ecological parameters, for example) they are all found to by one species, it would be nice – satisfying even – to put one valid name on them.  And… by examining the works of Dall and Bartsch, one can often find numerous – perhaps several dozen – entirely satisfactory species names that will fit within that single collection of specimens from a single species from a single small bay.

Amongst the references I downloaded (thanks to Google’s digitizing, many books in the public domain are downloadable) was:

Dall, W. H. and P. Bartsch. 1909. A monograph of West American Pyramidellan Mollusks.  United States National Museum, Bulletin 68. 1-258 pp, 30 pl.

This monograph contains 258 pages of species descriptions…  And 30 plates of illustrations…. As an example , take a look at this one.

This is one of many plates of illustrations showing species of TurbonillaTurbonilla is one of the genera of pyrams that has species that will attack Tridacna.  Do you think you could use such images as these to differentiate between any two them reliably?

Could anybody?

When I discuss specific animal groups in my articles for the reef aquarium hobby, I like to give examples of those species…

CORRECTLY IDENTIFIED examples of those species.

And, please excuse me, so that I may now go and start beating my head against the wall.

Because it will feel soooo good when I quit. 

An aside… 

Oh… for those of you who might know mammals, the Dall sheep and the Dall porpoise were named after William Healey… AND here is something I will bet you probably didn’t know.  His name “Dall” was pronounced rhyme with “Gal,” NOT “Gall,” as it is most often used.   See… I even give you a piece of “party” trivia to amuse your friends with.  Of course, if you do so, you risk never being invited to such parties again.

References:
Raup, D. M. 1962. Computing as an aid in describing form in gastropod shells. Science. 138:150-152.

Raup, D. 1966. Geometric analysis of shell coiling: general problems. Journal of Paleontology. 40:1178-1190.

Raup, D. M. 1969. Modeling and simulation of morphology by computer. Proceedings of the North American Paleontological Convention. September 1969:71-83.

Until later,

Cheers,