Nudibranchs
For quite a while I have wanted to post a number of my underwater images which were taken from 1975 through 1994, mostly in a few of the shallow water environs of the Pacific Northwest, a.k.a. the Northeastern Pacific. Most of these were taken to be illustrative, that is to show the animal or organism, primarily for lectures or in presentations, they were not meant to “artsy” images, although some certainly turned out that way. I finally have bitten the bullet, and am scanning a lot of these images into high-definition digital form, this being largely facilitated by the purchase of an external hard disk drive (HDD) of terabyte capacity, so that I actually have a convenient place to store the images. Judging from the size of the scanned images, I may well fill that HDD. However, I obviously can’t post such high definition images here, nor can I post them all, as I estimate I have well over 5,000 images. Consequently, I have decided to post a few every few days for the foreseeable future.
Unfortunately, the posted images are really not the best quality; the images scanned from my slides average about 80 Mbytes each, so, the images posted here are really quite low in resolution. Sorry about that, but it can’t be helped. In my scanning, the order is not random, but it is also not taxonomic. It is “slide holder order.” I had/have arranged my opisthobranch slides in slide holders in a loose leaf notebook with the nudibranchs first, but within that group they are in more-or-less haphazard order. If that bothers you, exit now and save yourself the heartburn. Once I get them all scanned, I will arrange them in some sort of logical order, but that is in the future.
The very diverse and species-rich array of animals grouped under the name “Opisthobranchia” were, until recently, thought to be related. That is no longer the case, and while some subgroupings within the old group, such as the nudibranchs, are good taxonomic groups, the term “opisthobranchia” is now obsolete and used only as an informal term, and one I suspect will die out over the next few decades. I hope you enjoy the images and the commentary that goes with some of them. The taxonomic nomenclature (i. e. the names) used in the opisthobranch image postings follows that given in the fine photo reference book: Beherens, D. W. and A. Hermosillo. 2005. Eastern Pacific Nudibranchs. A Guide to the Opisthobranchs from Alaska to Central America. Sea Challengers Publications. Monterey, California. vi + 137 pp. If I have made any mistakes in the listing or image names, those are mine and mine alone.
Hermissenda
Hermissenda crassicornis, the opalescent nudibranch. Photographed at a depth of about 10 m on the 4th of July, 1992 in Barkley Sound, Vancouver Island, British Columbia, Canada.
A pair of Hermissenda crassicornis, the opalescent nudibranchs. These were photographed at about 10 m on the 14th of October, 1983 near Ohiat Isand in Barkley Sound, Vancouver Island, British Columbia, Canada.
These nudibranchs are not social animals and their appearance together is probably happenstance. However, they may be getting together to mate. Unlike many other nudibranchs, particularly the dorid nudibranchs in which copulation may take many hours, mating in Hermissenda is anything but sluggish. As with all nudibranchs, they are hermaphroditic and mating is reciprocal. From start to completion, copulation takes but a small fraction of a second.
A Hermissenda crassicornis, the opalescent nudibranch. Photographed at about 12m depth, on the 2nd of June, 1982 in Barkley Sound, Vancouver Island, British Columbia, Canada.
The above opalescent nudibranch appears to be on a rock with brown algal filaments on its surface, but that is misleading. The scene is one of a small patch reef created by the annelid worm, Dodecacaeria fewkesi. What appears to be brown algal filaments on the substrate are actually masses of tentacles arising from the worms whose calcareous tubes are cemented together forming the reef.
And there is more going on!!!
The tall structures in the background are hydroid colonies; probably the nudibranch would be eating the hydroids if it were on them. The small white blobs on the hydroids are either individuals of another nudibranch, from the genus Doto, or that species’ eggs. During the spring, everything in this region grows like crazy, particularly those animals, such as the hydroids, that feed on plankton, which is very abundant. In this case, the hydroids, of course, feed on small zooplankton. Individuals of Doto species feed on the hydroid polyps and their populations bloom right after they hydroids have their growth spurt. These small nudibranchs, about 3 or 4 mm long, can have population densities exceeding 5,000 per square meter, and will be featured in an upcoming post.
Dodecaceria fewkesi, the “reef building” cirratulid worms. Photographed on the 28th of April, 1984 inDodger Channel, Barkley Sound, Vancouver Island, British Columbia, Canada.
These worms secrete the calcareous tubes that they live in. Dodecaceria individuals aggregate together, probably due to asexual reproduction as well as larval recruitment. In doing so, their calcaeous tubes fuse forming, first, what appear to be small rocks with worm holes in them. Later, as time goes on, these rocks grow by the addition of more worms. In doing so, they create one of the few types of reefs, other than those made by corals, that are biogenic, or made by living organisms. These worm reefs are never very large, but they can be as much at 20 to 30 (6 to 9 m) feet long and 6 to 10 feet (2 to 3m) high, or as big as some coral patch reefs.
A portion of a small reef built byDodecaceria fewkesi, the calcareous-tubed hair worm. Photographed on the 29th of April, 1983 in Pole Pass, between Crane Island and Orcas Island, in northern Puget Sound, Washington, USA. The slightly “foggy” appearance to this image is due to small plankton in the water reflecting my strobes’ light.
This image shows the small “rocky reef” made by the hair worms. This area in the San Juan Islands of Washington, was one of my primary research study sites in the early 1980s. In addition to the small patch reefs made by this worm species, there are other, much larger, reefs at this site that are made by a different type of worm, the sabellariids, and I will probably post images of them in the future. Most biologists don’t realize that corals are not the only reef forming animals, and when told of these worm-built reefs, often respond with disbelief and incredulity. Nonetheless, such structures are reasonably well-known and described in the scientific literature.
As with coral reefs, these worm reefs are “hot spots” of local species diversity. However, there small size and lack of much 3-D heterogeneity, limits the number of other animals that live with them. Nonetheless, opalescent nudibranchs, and the hydroids they feed on are often common on these reefs. Due to the distance from the reef, not much other life is recognizable in this image, though. The large white blob is probably a contracted plumose sea anemone (Metridium sp.), which when inflated fully would be a couple of feet high. The golden crescent near the bottom, is the aperture of a large scallop (Hinnites sp.) that is found in the area. These animals cement their shells to rocks, and unlike most scallops are immobile when they are adult. That individual is probably about four inches (10 cm) across.
Flabellina
There are lot of small aeolid nudibranchs found on, and eating, hydroid colonies or other cnidarians in the spring in this region. Here are a couple of shots relating to, and of, Flabellina trilineata.
The orange structure is a colonial hydroid, Garveia annulata, that was occasionally common in some areas that I dove in. The hydroid colony in this image is a couple of centimeters long. Notice the large orange “balls” (reproductive polyps), they are about 1/4 mm in diameter.
The three-lined nudibranch, Fabellina trilineata. This little nudi reaches lengths of about 1.5 inches (36 mm) or so, and is commonly found in the spring in rocky areas in the Pacific NW subtidal regions. It, like many aeolid nudibranchs eats hydroids, including Garveia.
This image shows a baby F. trilineata (notice the rows of tiny cerata growing on its back) eating Garveia. The nudi is about 2 to 3 mm (about 1/8th inch) long. You can get an idea of size by noting the reproductive polyps and comparing this image with the images of Garveia, above.
One of the activities I tried to do at times during my diving career was to take “extreme” macro shots of various invertebrates in the field. I had an apparatus that allowed me to get an image magnified up to about 12x on the slide; so, if the animal was 2 mm long, the image would be about an inch long on a 35 mm slide. In this case, the nudibranch in the last image above was magnified about 8 times. There were a lot of technical problems with taking these images, not the least of which was that the object to lens distance was very small, and that it had to be accommodated within my camera’s underwater housing. Given the water currents in the areas where these images were taken, even holding one’s position during the water flow, euphemistically referred to as slack water, could be difficult. The large camera and strobe housing caused an immense amount of drag, and severely limited my mobility. Other problems included looking through the viewfinder of the camera with a scuba mask on, and so on… Suffice it to say getting any sort of image was a problem.
The major difficulty, however, was getting enough light hitting the very small object to reflect back, passing through the underwater housing plastic, then the lens, and then the bellows that was on the front of the camera, and into the camera to properly expose the film. I began to feel like I needed a tactical nuke to take the picture. If I was able to successfully expose the object so that the slide was properly exposed, it sometimes felt like I need to produce so much light that it would vaporize the object I was taking photographing.
In the above image of the baby Flabellina on Garveia, the digital software “pushed” the exposure quite a lot, but doing so increased noise, and that noise is particularly apparent at the low resolution I must use here. That is why the image is a bit blurred. It can’t be helpped, sorry.
The next species of choice is Flabellina trophina, one of the more blah of the these normally spectacular wee beasties. Nonetheless, I have a fair number of images of it, as the species was common in some habitats I was investigating, and there were often not a lot of other animals visible there, so rather than return to shore with only half a roll of film shot off, I would take images of individuals of this species of nudi, and sometimes a few other critters.
Flabellina trophina. Photographed near Seattle in central Puget Sound, WA. in 10 m of water in 1982.
A head-on view, this image shows to advantage the extensions of the brown or tan digestive gland up into the cerata on the animal’s dorsum. “Cnidosacs,” specialized structures containing undischarged nematocysts from the animal’s previous dinners are located at the tips of each ceras and their presence is emphasized by the bright white coloration. This is probably aposematic or “warning” coloration for any visual predator, in these cases either a fish or crab that might consider this nudi a tasty snack.
Flabellina trophina. Photographed near Seward, AK in 10 m of water, in 1982.
This shows the animal in a side or lateral view; F. trophina can reach lengths of about 50 mm, or 2 inches. The structure visible on the animal’s right shoulder is the combined anal and genital apertures. All nudibranchs have their genital openings in this region, but the anus may vary in position, and that is – as one might guess – one of the characteristics defining each different subgrouping within the nudibranchs. The aeolidacea all have these apertures in position as shown in this individual.
Flabellina trophina. Photographed south of Seattle in central Puget Sound, WA. in 12 m of water in 1988.
I have no quantitative data, but my notes list several observations of this species feeding on sea pens (Ptilosarcus gurneyi). I was working on photodocumenting the events occurring in sea pen aggregations (called sea pen “beds,” for no logical reason known to human cogitation). Over some 20 plus years, I made, maybe, 150 dives in this habitat and took several hundred images. There will be slides of many other different animals posted during these excursions through my slides that were taken in the sea pen aggregations. Starting with some nice research by Chuck Birkeland the natural history and “ecology” of the sea pens in the Puget Sound region are probably the most well known of all pennatulaceans. In any case, I was photographing F. trophina in the beds not because it was documented to feed on the sea pens (it was not, even though I found that it is a common predator on them – or at least it was when I was actively diving in those areas), but rather because it was common and somewhat attractive, and sometimes, I just wanted to take its picture. 🙂 . I took the above image because it shows a lateral view of the animal with its snout elevated which is a common posture.
Flabellina trophina. Same images as above.
While I was preparing the scanned image for this post to the forum, which involved making lower (much lower) resolution images, I noticed what I thought might be artifacts due to fine hairs that got on the slide prior to it being scanned. And, gee, living in a house with a large hair factory, one that specializes in producing very thin, fine hairs (a.k.a. – my true buddy, Casper = “A Maine Coon Cat” = giant fur ball). I figured that if these were, indeed, fine Casper hairs, I would have to reclean the slides and try scanning them again. The “hair” images/artifacts are circled, and if one examines the image above this one, it is quite possible to see them without the circles. There are a lot more faint “hair-artifacts” visible than are circled.
My buddy, Casper, a generator of loose, fine hair, but not guilty of being the source of “hair-like” images on my nudibranch slides.
Flabellina trophina. Same images as above.
When I examined the fine “hairs,” I found that Casper was off the hook, they were not artifacts at all, but were actually part of the original image. They were microscopic phytoplankton floating by in the water as I took the images. As I described above, I could photograph microscopic subjects. Well, here is the inadvertent proof of that statement! And, it is something that I had never seen on the image before this scan!
I further enlarged the portions of the images in the red circles and included them in the original image. They are shown outlined in red and are indicated by the arrows. Note the “zig-zag” structures. Well, those structures are not 2-D zig-zags, but rather 3-D helices of chained diatoms. Here is a link to a photomicrograph showing similar diatoms in a better view.
WOW!!! I think this is REALLY neat, because it shows how what appears to be the relatively clear water in a photograph of an underwater scene may, in fact, be filled with plankton that are just below the resolution capabilities of either the camera or the printer or scanner to show. I have often heard a comment to the effect that a given tropical coral reef image shows water so clear that it is “obvious” that there is no plankton in it. I wonder how many of those images would show microscopic plankton of one sort or another if they had been taken with a better camera or printed in better manner.
No plankton present… LOL!!! Obvious, INDEED!!!
More images soon.
Until then,
Cheers, Ron
