AHABS... Issue Three

Look Sharp! Microscopy for the Reef Aquarist


Ronald L. Shimek, Ph. D.

It's A Small World

It is a paradox that as impressive as a beautiful reef aquarium may be, the vast majority of the living things in such a system are obscure or invisible to the aquarist. In this regard, it is a reasonable representation of the natural world. The oceanic organismal array covers examples of most types of life, from animal to algal to fungal to… well, pretty much you name it. Except for the green plants, represented by only a few species of mangroves and sea grasses, and the insects, represented only by a few species of wingless gnats and water striders, virtually all other types of organisms thrive and are diverse in marine systems. Many representatives of this unseen majority of organisms share one obvious characteristic. They are just too small to see clearly, or at all, by the unaided human eye.

There are several solutions to “the problem” of not seeing these organisms. The most common of these is simply to ignore them. “Out of sight, out of mind” is a motto practiced by a lot of reef aquarists and, I think, who can really blame them? Well, I can, but that's another story. Nonetheless, most people set up a reef tank for the visual pleasure it brings and they don't want to have to spend a lot of extra effort to see what they perceive, at best, as “little obscure creatures.” Interestingly enough, however, I have found over the years that I have been discussing the reef aquarium hobby, that a sizeable proportion of aquarists get really and thoroughly “hooked.” They become interested in virtually everything pertaining to their tanks. Often suddenly, and almost always surprisingly, they realize that their interests are not limited to the large and obvious things in their systems. Quite literally, a whole new world, then, opens up to them.

The beauty of many smaller organisms and non-living structures has been recognized and well known for a long time. That hidden beauty is one aspect that drives people into investigating the minute and wonderful miniature life in their captive worlds. There is another reason that many people are driven to examine small and minute things and that is, for some of us, an innate and intrinsic driving interest in the “small and complex.” For such people, and I rank myself with them, observing a small and elegant solution to a problem is often more aesthetically pleasing and interesting than observing the brute-force and bulky solutions to problems seen in the large world around us. All organisms have to solve the same basic problems in their quest for existence and propagation. These are “the fundamental problems” of all life, such as how to feed, how to avoid becoming the solution to somebody else's quest for food, how to sense the world, and...

The Cucumbers of the Sea


Ronald L. Shimek, Ph. D.

Echinoderm Worms

About ten years ago, one of the first columns that wrote for the aquarium hobby, in the print version of Aquarium Frontiers, was about sea cucumbers. I think it is time that I revisited that vast and vastly important group of animals. Although the cukes surely have not evolved much in the intervening few years, our aquarium systems have changed quite a bit; unfortunately, our ability to support and maintain most sea cucumbers has not appreciably increased.

Classified by taxonomists as belonging in the Class Holothuroidea within the Phylum Echinodermata, sea cucumbers are some of the most bizarre animals in that phylum of most bizarre beasts. There are an estimated 500 species of sea cucumbers and, generally, they are of moderate sizes. The smallest are about 1 cm (0.4 inch) long, as adults, the largest may get to about two and half meters (8 feet) long. The main distinguishing characteristic of echinoderms is their radial symmetry, and coupled with that, the total absence of a head, front end, or back end. For a sea star, normally the epitome of echinoderms, any direction surrounding the animal may be in front of the animal, for all it has to do is to start moving in that direction. Sea cucumbers, on the other hand, are basically cylindrical and therefore differ significantly in orientation from the sea urchin spheroids and the stellate asteroids.

When first encountered, sea cucumbers look like worms as they are cylindrical and elongated along an axis leading from their mouth to anus. Nonetheless, they appear decidedly more normal than do most echinoderms. At least their distant ancestor's past evolutionary decision as where to place “fore and aft” corresponds to that made by most other animals. More correctly put, I suppose, is that they are more normal than the average echinoderm in even having a “fore and aft.” Most animals have a front end and a back end, but for the cukes, it really is bucking the echinoderm trend to do so. However, just to be good echinoderms and stay on the distaff side of boundary of good taste and decorum, sea cucumbers have NO development of any structure remotely resembling a head at the front, hind end, or anyplace in between. The mouth is at one end, it is true, and as the animal often moves in that direction, it may be referred as the “front” end. But, just as vacuum cleaner has no head over its business end, neither does any sea cucumber. On the other hand, and as in most animals with a mouth and appendages, at least some of those appendages are associated with the mouth and are used to handle food and to assist in feeding. In the case of sea cucumbers, the mouth is surrounded by five or ten tentacles, and these transfer some sort of particulate food to the mouth...

The Ciliated Protozoans - Almost Animals


Ronald L. Shimek, Ph. D.

Size and Simplicity

In this article I will discuss some of the most common and abundant, albeit invisible (mostly), inhabitants of both real and artificial reefs. In an issue of AHABS devoted primarily to microscopy, it is fitting to spend a bit of time ruminating about microscopic organisms. In particular, the organism I will focus on are found grouped under the name “Protozoa,” from the Greek “ proto ” meaning “first or primary,” and “ zoon ” meaning “animal.” However, this term is a holdover from days not so long gone; when these groups were considered animals - and primitive ones at that. In our present state of knowledge, based primarily on the similarity, or lack thereof, of their genetic material with that of other creatures, they are considered to be one of several groups that have the same “level” of distinction as either animals, plants, fungi, or many of the algal groups. This would put them into one of several “Kingdoms” in the domain of “Eukaria.” In other words, their bodies are made of cellular components bound in membranes, but they are sufficiently distinct and unlike other organisms with such subcellular constructions that they are may be put into their own “Kingdom.” Just which Kingdom that might be is open to discussion; in fact, the revolution in comparative genetics that we are in the midst of is happening so fast, that there is some real question about the utility of the very levels of the taxonomic hierarchy itself. It is possible that a wholesale revision of the conception of taxonomy is at hand, and that they (and all other organisms) may soon find themselves categorized by humans in some new and exciting way. In any case, their taxonomy notwithstanding, good references which would discuss these organisms in greater structural detail, at least, would be standard invertebrate zoology texts such as Ruppert et al, 2003. Given the speed with which information is being accumulated at the present time, even recent textbooks will be out of date concerning the relationships between these and other organisms. A lot of useful, more up-to-date information may be obtained by searching the World Wide Web; I have included some few links to online information in this article but, if you are interested, by all means, dive in… the web is full of ciliated critters.

As we presently understand many of these groups, some of these protozoans are relatively primitive (which is defined as being near the ancestral condition) creatures. These would include such organisms as amoebas and foraminiferans. Many other “protozoans” are quite advanced or derived. I think it is useful to consider as you think about the protozoans whether you want to discuss them as being made of one cell (unicellular) or as having bodies without cells (acellular). They can be treated either way, but there is often a subtle and significant bias introduced with the former condition. For example, if they are unicellular, that is made of “just” one cell, and as all "good" animals are multicellular, there "must" be something inherently inferior about the...

Ron Shimek