PART  1

They are here included many pictures published by the kindness of his authors to which I forward my more sincere thanks. Especially to M. Verolet, whose generosity has provide many of the most interesting pictures shown here.  I have also borrowed drawings of some sites of Internet for which I give the needed notice. The remaining illustrations were taken (in these times of digital cameras with 5 to 10 Mpx) with a camera of 0.4 Mpx.; certainly they are treated vastly by PhotoPaint, NetImage Demo, and ACDSee.

I hope that, at least, they would be clear and convey the information that they are intended to give.

INTRODUCTION

In traditional taxonomy Rotifers are considered a Phyllum which embraces three Classes: the “Seisonacea”, the “Monogononta”, and the “Bdelloidea”.  Seisonacea are only marine, epizoïques on Nebalia, (a genus of crustaceans considered very primitive, benthonic, with some littoral species), and are represented by only one genus, Seison, with three species, the last one published in 2007, which have a morphology very distant from that normally assigned to a rotifer.   Monogononta, thus called because male and female have only one genital gland, were vastly treated by Michele Verolet, which has even presented in the French Magazine Microscopies a very complete and much illustrated description of its morphology, and a splendid key to identify all the genera that the amateur has the possibility of finding with some frequency in its explorations.

http://www.microscopies.com/DOSSIERS/Magazine/Articles/M%20Verolet-CLE/presentation/presentation.htm

Bdelloidea are all parthenogenetic females, with two genital glands. (During a long time they were called Digononta).

 Monogononta and Seisonacea have males. But Bdelloids do not have them ....... probably since 80 million years
(http://news.bbc.co.uk/1/hi/sci/tech/7039478.htm)

Its reproduction is exclusively parthenogenetic, and the genetists break their heads to discover the mechanisms which made it possible for these animals to maintain its genetic diversity avoiding to be banned from the list of the living species. Some recent papers show that they steal genes from other species, to modify her own genome.

Of all the Rotifers the Bdelloidea are the best known by the non specialized students. The cephalic end of the majority has a “corona” divided in two retractile “trochal discs”, with ciliated margins. The Cilia in the “trochas”, that beats metachronically, and seems to rotate, gave the name to these animals. In fact the trochas are restricted to 15 of the 19 genres of this Class, but they are so showy that the not informed identifies not only the Class, but all the Phyllum Rotifera, with the bdeloids.

2 - Magnificent frontal view of the “head” of a Philodina (courtesy of Charles Krebs). Click on the picture to see a labeled version

2b - Annotations of the author: 1 lines of cils implanted in the trochal edge (2), 3 inferior lip or Cíngulum, 4 lip of the buccal funnel, 5, buccal funnel, and 6 sulcus (a furrow between Trocha and Cíngulum) These ciliated fields help to send the food to the mouth.

They are multicellular organisms with a fairly complex organization, but its size is in a scale similar to that of the big protozooa. (Between 150 and 700 microns. Only one species, Rotaria neptunia, she is excessively long and thin, reaching a measure of 1600 microns. (Ricci and Melone, 2000)

Practically all the species can endure drying and can revive when they happens to be submerged in water another time.

 Jacobs published in 1909, for the first time, the description of this amazing capacity of the rotifers, which gives them the possibility of invading really difficult habitats, like desecables mosses, the cracks in the crusts of the trees, the ground, and so on.

The rotiferologist Aydn Örstan was able to find bdeloids in the wall of the tubes of thermites, adhered to a tree in Puerto Rico, and even to describe a new species from the dust on the soil of a dessert in México.

 Christian Colin experimentally registered the images of the drying process and the reviviscence of a bdelloid. The article that describes his technique, process, and results can be read at:

http ://www.microscopies.com/DOSSIERS/Magazine/Articles/CC-PHENIX/Phenix-1.htm

and its second part

http ://www.microscopies.com/DOSSIERS/Magazine/Articles/CC-PHENIX/Phenix-2.htm

another shorter graphic document on the same phenomenon written by Hugo Baillie-Johnson can be found al   http://www.microscopy-uk.org.uk/mag/artnov02/hbjtrehalose.html

3 - Reviviscencia, after 46 days of anhydrobiosis. Registered by Christian Colin

 In the state of anhydrobiosis (or anabiosis) they resemble small dust particles and, like them, they could be dispersed easily by the wind, or the waters that bathe the surfaces where they are. Notwithstanding there are in fact few registered data on the real (and surely multiple) methods that the rotifers use, and which have given to many species the ability for them to become cosmopolitan.

The anydrobiose is not a simple adaptation to difficult to colonize habitats. As Ricci et all. says (August 2007)

 Bdelloids, although aquatic animals, are not only efficient in tolerating desiccation, but seem somehow dependent on anhydrobiosis, a circumstance that might represent a key event in their life cycle. If this is true, life in unpredictable habitats should not be seen as the result of competitive exclusion from 'easier' habitats, but a requirement for long-term survival of these parthenogenetic animals”

The name “bdeloids” comes from the Greek and it talks about the characteristic way of crawling in a leech-like manner, fixing alternatelly the terminal toes, extending, fixing the rostrum, and retracting the previously fixed end.

 Also in this case all the bdeloids do not show always the same behavior. For example a rotifer of the genre Adineta moves normally gliding over surfaces, using the cils that cover the ventral side of their cephalic end. (see picture xx)

 Even the cephalic end, wich gives his name to the Class, does not have a homogeneous structure, and there exist at least 3 different structures, which allow to divide the class in 3 Orders: Adinetida, Philodinida and Phylodinavida, and will be treated in detail when characterizing them.

As in the Monogononta (See Verolet

http://www.microscopies.com/DOSSIERS/Magazine/Articles/M%20Verolet-Les%20Rotiferes/texte.htm)

the body is compossed of 3 basic portions: the head, the trunk and the foot. The epidermis that covers it is a sincitial layer (that is to say, a layer of cytoplasm in which separated cells do not exist, although these are represented by big dispersed nuclei) is marked by cross-sectional furrows that separate superficial ring (pseudosegments, since they do not divide the interior of the body), and that gives to the rotifer the capacity to be contracted in a “telescopic” way. This is possible thanks to the existence of a pliable layer of intracytoplasmic cuticule, denominated “lorica”.

 In many Monogononta this lorica is hard and indeformable, with important specific characteristics. (See Verolet) But in the Bdelloidea it is almost always thin and folding, although in some species they can have characteristic thickenings denominated “Cuticular Sculptures” (plates, furrows, spines, warts, a.s.o).

 The “corona”, when it exists, can be closed inside the head, and this, and the foot at the other end, are contracted within the trunk, acquiring a compact and rounded form. This form (named “tun” in English) is the one that they adopt so much as a strategy of defense in any case of a sudden aggression, or even as a previous step to drying. (see the above experiment of Christian Colin)

4 - The immediate total retraction of a Philodina as a reaction to an abrupt contact, like a stroke over the coverslip

  It is common that the head joint to the trunk by a narrowed portion called the “neck” Normally a sensitive antenna, thin, and more or less long, lodges dorsally in the “neck”.

5 - Lateral view of a Philodina sp. , showing the dorsal antenna. Below the antenna can be seen the red eyes . The pseudosegmentation and the ridged trunk cuticle is also shown.

 In addition,  between the “trochas” it can be seen dorsally  the “Rostrum”, one generally robust structure provided at its end with cils, sticky cells and sensitive lamellas. It is retractable in most of the species.

  Some species have eyes, which lodge sometimes in the anterior end of the rostrum (Rotaria), and other times dorsally in the neck, over the brain (Phillodina). In Adineta oculata they are described rostral eyes composed of a red spot surmounted by a concave lens.

6 - Dorsal eyes over  the brain  in Mniobia. They are pigmented of red.

7 - Rotaria sp., dorsal view of the head, with dark eyes in the rostrum

8 - Relation between the antenna and the rostrum. Trochas semiretracted. One specimen with the “Corona” totally retracted is seen in picture 27

The mouth opens centrally between the “coronas” (see fig 2) at the end of a buccal funnel, which could be followed by a buccal tube that communicates with a masticatory organ named mastax.

The length of the buccal funnel and the buccal tube, and the depth of the mastax is a character that depends on the style of alimentation.

You can see a mastax very near the mouth at fig. 30 (Henoceros)

 The Mastax is a complex organ formed by strong muscles armed with several hard, cuticularized pieces, named “trophi”. Its structure is characteristic of all the class and it really has little variety. The type of trophi of the bdelloidea is called “ramate”. The ramate trophi lacks the fulcrum, one unpaired piece characteristic of the remaining types of trophi of the Phyllum. (Ver Verolet) The trophi consist of 6 pieces, 2 unci (sing. uncus), 2 manubria (sing. manubrium) and 2 rami (sing. ramus). The plate-like Unci are armed of teeth, differentiated in 3 groups. The anterior and posterior ones, are formed by thin teeths. There is a group (generally median) that has much more heavy teeths. According to the genre and the species these heavy teeths can be in numbers from 2 to 10.

                      
10 - Typical image of the trophi of the order Philodinida, courtesy of M. Verolet.

 It can be compared with this image taken with electron microscope, and colored to differentiate the different pieces. In red the manubria, in blue the unci and in green the rami, underneath the indented edge of the unci

                                           
11- MEG image of the ramate trophy electronically stained, due to G.Melone.

 12 – Something atypical Mastax of a Philodinavida from Cancún  (5 images composed with combineZ 5.0)

 Moreover the trunk lodges the remaining organs in its interior: brain, sub cerebral and retrocerebral organs, mastax, salivary glands, digestive and excretory systems, gonads, and muscles.

               
13a – Mastax, salivary, glands and intestine with heavily ciliated lumen in a bdeloid. Courtesy of M. Verolet.

 The mastax is followed by a normally very short esophagus, in most of the cases difficult to see, which opens in the sac-like, stretched, stomach. Normally the stomach is syncitial, with a ciliate cavity (mostly a tube) which is followed by a short, mostly bulbous, intestine (some times called “rectum”). But in the Habrotrochidae the stomach has no lumen at all and food is worked out in little balls, and included in vacuoles that give to the stomach a foamy appearance.

 
13b - The stomach of an Habrotrochidae

 Behind the rectum, or underneath, we can see the urinary bladder, which gathers the liquid retired from the pseudocoel by two long protonephridia culminated near the neck by some flame bulbs. Blader and rectum both finish in a common “cloaca” that opens to the outside dorsally in the base of the trunk.

 The reproductive apparatus is represented by two germovitellaria, organs that produce eggs, and at the same time provide it with the vitelo (nutritive material) necessary for its development.

                                         14 - Germovitellaria at both sides of the intestine, in the trunk of  Adineta sp.

 Most of the bdelloidea are ovipares,

                                    15 - A finished Egg, inside a bdelloid

 But there exists some cases of viviparity. And some times the already formed embryos, even mobile ones, can be seen within the mother. Even if the development of the embryo is not advanced, viviparity can be denounced by the fact that the egg is seen as pluricelular. 

16a - Segmented egg (embryo) inside Rotaria sp. Note the abscence of a Shell and the irregular surface.

16b- embryo and another segmented egg in Rotaria sp.

 The segments after the anus forms the retractable foot, at whose end 2 spurs can be normally seen, and behind these ones, a short structure lodge the toes, connected to glands, visible in the last portion of the foot,  which produce sticky substances, allowing the rotifer to adhere to the substrate.

  In a few cases (Bradiscella, Mniobia, and some epizoics) these toes are replaced by a sticky disc.

17a – spurs in the foot of Mniobia, note also the big egg

17b – adhesive disc at the end of the foot in Mniobia

17c – toes at the end of the foot of Rotaria (courtoysie of Bertrand Parres)

 I add here 3 tables with the list of the known genera, ordered under three different criteria. This can be redundant, but I think that it is an easy form to convey very interesting information

LIST OF GENERA IN ALPHABETICAL ORDER 

(in blue, epizoic genera)

Genus, author, publication date, aproximative species numbers

A still mentioned (especially in text books) genus (Callidina) is not valid now, it was very heterogenous and the described species have been distributed, between many of the now accepted genera.

 2) Genera ranked by number of species

3) Genera ordered by the publication year

                   No new genera has been described in the last 92 years