Rotifer Chats

May I start this series of "chats" by saying that they are not intended for the advanced student of the rotifer, but for those who are just starting this study and are looking around for some simple literature to help them on their way, and also for those who like to take a collecting net and bottle to the pond, just for the sheer joy of beholding under the microscope the " wonders of nature" that are to be found in a tiny drop of water, and who are sufficiently interested to like to be able to identify the rotifers they find therein.

Putting it shortly, then, I hope to try and write the kind of article I should very much have liked to have had available when I first started in this line. I have found that many would-be rotifer students have been put off by the highly scientifically correct articles and lists of species that one sees on this subject, and also by people who, as an old friend of mine once said, "try to blind one with science." I would like to assure anyone who has a little time to spare that they would like to devote to this study, that they can have lots of fun apart from, or in addition to, useful study, without having to attend biological classes (although of course this would be a great help if one had the time and facilities to do so) by using their powers of observation coupled with plenty of patience and the available literature (on which I shall have more to say in a later chat). Also, I shall be only too pleased to help at any time anyone who would care to write to me c/o The Editor of Micro Notes.

Although I intend to write these articles in a plain, not too technical manner, I shall endeavor to make all descriptions, drawings of species, etc., as up-to-date and correct as possible, and if anyone objects to what I say in these chats or thinks I am wrong on any subject, I only hope that he (or she) will write and say so, as by doing this they can be of help to us all.

The Rotifera were first observed in the latter years of the 17th century by the pioneer microscopists, who called them "wheelbearers", since one of the first rotifers discovered was one of the Bdelloids, probably of the genus Rotaria, whose corona consists mainly of two circular discs surrounded by cilia, borne on pedicels or short stems, which resemble two small cogwheels in motion when the animal is swimming or is anchored by its toes and feeding. Since then, owing to their great beauty, interesting habits, and to the ease with which they can be procured, the Rotifera have been great favorites with many amateur micro-biologists the world over. They are common everywhere there is water; in lakes, rivers, ponds, ditches, birdbaths, and often even in roof guttering and mosses.

POSITION IN THE ANIMAL KINGDOM

The Rotifera have in the past been classed with the Infusoria, and they are also stated by some Zoologists to be related to the worms and Polyzoa. Grove & Newell, in "Animal Biology", put them in a Phylum of their own.

The Rotifera are a peculiar group, probably one of Nature's offshoots, which appear to have come down from prehistoric times in very much the same form as they have today. This I think is rather borne out by the fact that the same species, or many of them, are found all over the world, and there are very few, if any, species which are localized in any particular country. This is particularly noticeable in the island continent of Australia, where other forms of animal life are in many respects much unlike those found in other parts of the world (i.e., marsupials or pouchbearers, etc.) but the known rotifer species are the same as found elsewhere.

Rotifera are chiefly confined to fresh water; some few are marine, some brackish, and a few species occur in both fresh and brackish waters. They are therefore one of the few groups which can fairly safely be said to have originated in fresh water.

ANATOMY

The Rotifera are small, if not the smallest, Metazoa or many-celled animals (distinct from the Protozoa or non-cellular animals, in which specialized parts of the same cell carry out all the necessary functions of the animal). Briefly, a rotifer is a minute animal, typically with a ciliated trochal disc for locomotion and food collection, a complete alimentary canal with anterior mouth and posterior anus, and a muscular pharynx with jaws or trophi unique to this class of animal; excretory system with flame cells joining the rear gut to form a cloaca; simple nervous system with brain; and, usually, a pigmented eyespot. The body is often enclosed in a transparent shell or lorica, and in many species there is a foot terminating in two toes.

There are of course many species of rotifer (approximately 1,500) but this description fits most species. One of the most striking features of the rotifera is the jaws or trophi, which is not to be found anywhere else in the Animal Kingdom. The movement of these jaws or trophi can be seen ( in many species) quite easily even under a low-power objective such as a 1 inch or even a 2 inch. They are indeed a good means of identifying a rotifer (excepting the male, which in most species has no jaws) from any other small animal. In addition rotifera, unlike the protozoa, have the cilia used for locomotion on the front part of the body or head only; this also is helpful in making reasonably sure whether the animal at which you are looking is, or is not, a rotifer.