Trichodina: Ultrastructural details (part I)
Posted @ NImag by
Guy Sawle
Canadian Koi and Pond shares this article with the permission of Guy
Sawle; this article and photographs are not to be used elsewhere with
out first being granted permission by Guy Sawle.
At the end of a recent thread on Trichodina I promised some more detailed information and electron microscope images. This has come about because I borrowed a book on ‘Protistology’ from the University science library [reference 1, below]. The book was so good that I emailed the principal editor (Prof. Dr. Klaus Hausmann in Berlin) and he sent me copies of some papers he has published on the subject. He has also very generously allowed me to post copies of some of his remarkable electron microscope images of Trichodina.
First, below left is a drawing of Trichodina pediculus (which lives in large numbers on the external surfaces of the freshwater medusa, Craspedacusta sowerbii). I am showing it alongside one of my recent pictures of a trichodina from my koi ‘China’. I do not know if this is the same species or not (probably not) but this does show the general arrangement of the beast.
As previously pointed out, there are two sets of cilia – those close to the holdfast organ, and those on the other side which is the ‘mouth’ side. The section at below left (taken from reference [2]) is an electron micrograph view through the edge of the lower ciliated area. There are three ciliary components close together. The main ciliary wreath (called the locomotor fringe) has many rows, each of which contains eight cilia, aligned obliquely. These can be seen in cross section in this picture, in the region labeled ‘cwc’ (circular wreath of cilia). Above and below this are further sparse rings of cilia. The one at the bottom, closest to the holdfast organ (here called the adoral disc, a.d.) is marked b.r.c. which is the basal ring of cilia. The one at the top is marked l.c. which is the lateral cilia ring. The scale bar at top left is 1 micron.
The internal structure of cilia is very similar in all ciliated protozoa. There are usually nine pairs of microtubules surrounding two more pairs. This is referred to as a ‘9 x 9 + 2’ arrangement as shown in the lower right picture (which is a cross section of a cilia from another protozoan).
The cilia are connected to structures called kinetosomes in the main body of the animal; it is the kinetosomes that make the cilia move.
The ring of cilia at the other (oral) end of the creature are arranged in a spiral which winds anticlockwise and terminates in the buccal cavity. This can be seen in the diagram above, but also in the in vivo contrast interference micrograph shown below (this one is Trichodina domerguei megamicronucleata; reference [3]). AC is the adoral ciliary spiral and the arrow points to the entrance to the oral cavity. It is this spiral of cilia, of course, that leads suspended bacteria to be captured by the organism.
Finally, the following picture illustrates the oral cavity in cross section. This extraordinary electron microscopical section is from reference [2] but is also included as plate 145 in reference [1]. It clearly shows the oral aperture (=mouth, =oral cavity) near the centre. You can also see some of the oral ciliary spiral in cross section (no legend). The macronucleus as seen in the top two pictures is very clear, as is the micronucleus (min). CV is the contractile vacuole, of which perhaps more at a later time…..
FV refers to a food vacuole. Interestingly, there are bacteria not only in vacuoles (where I believe they are food) but also free in the cystoplasm. The cytoplasmic bacteria are thought to have a symbiotic relationship with the trichodina (i.e. each benefits from the other) and this is quite a common thing in ciliates.
I hope you enjoy looking at these pictures. These are images from a true professional.
As ever, any feedback will be gratefully received.
Guy
[1] Protistology (3rd edition) by Klaus Hausmann, Norbert Hulsman &
Renate Radek. Published by E. Schweizerbart’sche Verlagsbuchhandlung,
Stuttgart. ISBN 3-510-65209-6, 2003.
[2] Hausmann K & Hausmann E. Structural studies on Trichodina pediculus (Ciliophora, Peritricha). I – The locomotor fringe and the oral apparatus. Journal of Ultrastructure Research 1981; 74: 131-143.
[3] Identification and ecology of Limnetic Plankton Ciliates. W Foissner, H Berger, J Schaumberg, Bavarian State Office for Water Management, Munich 1999. Reports issue 3, 472-479.
Guy
