I know that he would have really
appreciated this article.
Fig. 1 - an image of a very
probable St. muelleri.
Click on the image to view the original
captured this image, and the others of this species, in a population
in an aquarium with hard water, at Cancún,
(aka stentorbleu) was a Frenchman who 4
years ago did not even
At the time of his sad decease some weeks ago he was a
microscopist with a good theoretical knowledge, high manipulative
of sorting out the trophi from a rotifer's mastax and take high
images of it, and to manage to study and photograph difficult species
of Stentor. He was
also until his death a notable and indefatigable
palynologist and an
incredible correspondent in the French microscopy forums. Separated
were by an entire ocean we became good friends. This is my humble
that doesn't give up to his sickness and converts it into an
of this article is to
reader, who has never engaged in taxonomic research, to follow me
maze of data that will finally allow us to develop the key which was
initial objective of this work. I suggest that this article should be
read carefully. I hope that at the end of the journey, after having
consulted the documents which are suggested, reading the text a few
times and carefully observing the images, the microscopist with
little or no taxonomic
experience will have a better overview of the subject and, especially,
will be able to really give a name to their specimens.
As I state in the
paragraph on methods of
observation and documentation, the simple photographs taken by
most microscopists do
allow a precise species determination. Names applied to the specimens
compatible with the key. But the absence of any complementary data
"probable" identifications. I hope that in the future any
microscopist having a Stentor
under their objectives (including me, of
I have the chance to find them anew) compiles all the relevant
information which they will need to do a positive identification.
which readily draws the attention of microscopists who observe
the freshwater protists, is Stentor,
whose first species was named 231
ago. Generally of large size, sometimes numerous, and very frequent,
is easy to study even with low powers. The desire to give a
specific name) to the studied specimen conflicts with the shortage of
descriptions in the reference books.
intention was to produce a small key of the more common species
of the genus. But, aside from the difficulty in deciding which species
exclude, the study of the subject made me more interested in a broader
key, to encompass not
only the Stentor
genus, but also the family which includes it and two
other closely related families. This article is the result of all these
The heavily annotated key
that I add at the end, tries to offer microscopists the best
taxonomic determination of their specimens. One cannot however regard
as infallible. A few characters from one key, even if they are
not enough to replace a complete description of the species. The big
that faces the taxonomist (professional or not) who is interested for
the first time in the stentors
is clearly illustrated by the number of publications on the genus,
according to Foissner and
Wölfl 1994 exceeds 1300.
of each species can present great
variations, which can require for their definition a somewhat
study, with advanced techniques, like silver impregnation for
specialists have not even been able to completely agree on the
characters that are
used to define and to differentiate the Stentor
There exists however
series of characters which can be observed
without ambiguity with average powers and which make it possible to
the primary identification of even live specimens. These characters
are, in order of ease
1 - presence or
absence of symbiotic algae,
2 - the shape and
size of the nucleus,
3 - the form of
the apical sector or peristomial
bottom, and the presence or not of one "buccal pouch",
4 - the presence
or not of pigmented granules between the longitudinal lines of
5 - obviously the
color of the pigment if it is present
6 - the
existence or not of a total
or partial gelatinous tube (lorica) in which the individual lives
2 - description of the anterior end of one Stentor roeselii (silver
impregnation): AZM, Adoral Zone of Membranelles. BC, oral cavity. Ma,
Macronucleus. PBC, Ciliary lines of the "peristomial bottom", PM,
membrane. SC, ciliary somatic lines. Figs. 2-6, different nuclear
vermiform, 3 nodular, 4 moniliform (in chain), 5 only one ball, 6 more
ball. Fig. 7a- peristomial bottom with a "buccal pouch", 7b shows a peristomial bottom without "buccal pouch".
(One of the lines of cilia of the peristomial bottom is drawn for
showing better the
position and form of the
pouch. Figs 1-6 modified from
Wölfl 1994, Fig. 7 modified from Kumazawa 2002.
3 Stentor amethystinum - AZM
sinking to the mouth. In this and the following pictures we can see the
ectoplasm with its pigment granules and the zoochlorelles.
4 Stentor amethystinum -
disposition of the ciliary lines (clear lines) and the bands of
pigmented granules. The background is strewn with zoochlorelles.
5 Another species, showing
the cytoplasm deprived of zoochlorelles, but
with food vacuoles full with chlorelles. See the moniliform nucleus.
|above three images
from Christian Colin
|Fig. 6 - prob. St. Muelleri from Cancún.
We can see the lines of ciliary insertion. Fixed with hot AFA, stained
with Fast Green, mounted in NPM. In the right insert the moniliform nucleus
ellipsoidal beds is shown.
7 - Stentor
picture in phase contrast. Although the inner details are not
very visible, cilia differentiate in short somatic cilia and stereocilia
or rigid cilia, more dispersed than the somatic ones.
Fig. 7 reproduced
by the kindness of Rick Gillis, PH.D, from his site
Some confirmatory characters,
better observed with a larger power (400x), are the width, the
the position of the longitudinal bands of ectoplasmic granules, the
the number and distribution of rigid cilia (stereocilia) between the
the size, and forms of the extended individuals.
Conditions for the identification
study is essential. The best data at weak enlargement (40x and 100x -
objectives 4x and 10x, with an eyepiece 10x) will be obtained on
fixed on a substrate and extended in their normal attitude of food
specimens can be anaesthetized by mixing carefully in the liquid which
them small drops of a 1% solution of
sodium or potassium iodide, but it is very difficult to obtain a
anaesthesia in conditions of total extension.
The use of
enlargements (400 - 1000 X) can be used only on specimens carefully
between coverslip and slide. One can resort for this "to the petroleum
jelly compressors". Lubricate the palm of the hand with a very thin
of solid petroleum jelly (Vaseline) and pass on both opposite borders
of a coverslip.
With a micropipette select one or several individuals and drop them in
the centre of a slide. Apply the coverslip over the very small drop of
water containing the protozoa, in
such a way that the drop remains in the centre of the cover. By using
one or two mounted needles, the small quantity of petroleum
jelly will make it possible
to apply and vary the pressure on the specimens, while the
borders will allow water addition, anaesthetics or other reagents with
If one wishes to
make longer observations, use a seal with paraffin, or a microaquarium.
Using phase contrast illumination can be useful to
define ciliature and even better to identify rigid cilia, but it does
suitable for the study of internal organization, because there exists
cytoplasm too many inclusions of very similar index of refraction. It
advisable to try the darkfield stops and contrast filters. The
observed in all possible positions, as it is free, or as adhered to the
substrate, if it is sessile.
Many of these
details and especially the color of
the ectoplasmic bands of
granules, can only be interpreted by microscopists,
the direct examination of the live individual.
To highlight in
pictures the required identification details, they must be taken at
and with a high resolution digital camera (if possible with a 2 or more
on the important details (e.g. ex. stereocilia).
- As well as Kahl’s
1935 basic and
irreplaceable work, we
consulted that of Corliss
1961 and Foissner and Wölfl 1994,
which carries out a brief
but complete and informative revision of the genus, by treating all the
species, almost 50,
described after the traditional work of Ehrenberg 1838. They
recognize as valid only 18
of those species.
of other specific names have been applied to specimens or populations
with the current techniques are considered simply badly studied, or are
synonyms of the recognized species.)
2002, who studies the differential traits between some of the
species with moniliform
nucleus, recognizes as valid, one species that Foissner and Wölfl considers
invalid, and adds a new
species from Japan.
The Lynn 2002
summarizes the genera and the type species of ciliates is also very
useful to see
in detail the position of Stentor in
the traditional taxonomic system of Ciliatea.
Lobban et al. 2002 and Song and Wilbert 2002
new genus (and species) of Stentoridae.
I thank very much Professor Daniel
Nardin, whose kindness
and effort allowed me to
consult the article of Fauré-Fremiet
1936, on Condylostoma
will be much commented on subsequently.
Systematic position of the Family
consider it worthwhile to include in the key, the 21
species currently recognizable of the genus Stentor,
even if the microscopist probably does not find frequently
more than 4 or 5 species.
Below are links providing an introduction
to the taxonomic categories and
traditional hierarchies. If the reader does not have any background on
suggest they must be your
first reading (at least the
Classic classification scheme:
to understand the modern
Parts of a specific name
Stentor multiformis (O F
Müller, 1786) Ehrenberg
1 - name of the genus (it is always
written with a capital letter)
2 - name of the species (one always writes it with small letters)
3 - name of the researcher who described the species for the first time,
but probably in a different genus, and
dates of the description.
4 - name of the researcher who assigned the species to the correct
genus, and year
of the revision work
When there have not been modifications of
the name since its
description one only uses 4, ex:
dinoferus Lobban et
al." (and others), indicates that the authors of the specific
than two (see the complete title of the work of Lobban and his
associates, in the references).
relations according to Lynn
2002 (see the references).
Phylum Ciliophora Doflein, 1901
Family Stentoridae Carus, 1863
Having been established
almost 140 years ago
the Family Stentoridae
has a long and complex history. In the times of the monumental work of Kahl 1935, it included also
the genus Fabrea and Climacostomum.
In 1961 Corliss considered
valid the genus Stentoropsis
created by Dogiel and Bychowsky in 1934. This same year
(1961) Vuxanovici included
a genus, Parastentor, with only one species, which raised to 5 the genera of
the family. In 1972 Fabrea
and Climacostomum were
shifted by Repak to
genus was questioned, and
consequently Stentor and Stentoropsis only remained,
until 1978 in which
year Jankowski (in an
written in Russian) proposed to separate the species Stentor
auriculatus Kahl 1935 in a new genus Condylostentor.
However in 1936 Fauré-Fremiet,
had already proposed this species, which he described and illustrated
detail from specimens collected at Concarneau (Bretagne, France),
as a member of the genus Condylostoma, corresponding to the family Condylostomatidae,
and its criterion
has enjoyed more acceptance from the protozoologists, who rejected Condylostentor, created without
bringing a valid criticism to the work of Fauré-Fremiet.
continued to be a family
with only two genera (one of them very poorly known) until 2002 when almost at
the same time two new genera Maristentor
and Heterostentor, were
described and appear to be accepted for the moment.
On Parastentor, Stentoropsis and Heterostentor we will make some comments below.
the families closely related
to the Stentoridae. I
propose a key for the reader to recognize the three families. Read
I include extended comments and some images between the various
The key is based on
selections. There are only two options, one is true, the other not. You compare
your specimens with the options and decide which is in conformity with your
material. The option gives you a denomination, or sends you to another
Read the key as follows:
means that if option A is not
you must pass to the option B.
at the end of the line means that if your material is
in agreement with A
you must continue to seek in the option C.
Peristomial bottom ciliated,
without undulating membrane or with a rudimentary one ………….......................................................................................................................................................C
Body large, (700-900 microns)
contractile; with one undulating
membrane very visible on the right* anterior end;
Zone of Membranelles (AZM)
delimits a peristomial bottom without cilia
With one vast
peristome, V shaped; macronucleus moniliform
…………………………..................................................... Condylostoma Bory
de St. Vincent, 1824
Some species of Condylostoma can be
Stentor auriculatus was
included in Condylostoma
auriculata, since it has the characteristics
of the family and the genus
(undulating membrane, V shaped peristome, peristomial bottom without
moniliform nucleus.), (Fauré-Fremiet
Note: Kahl presents
and illustrates moreover S. auricula Kent 1881.
In the illustrations of Kahl, both species are fixed at the substrate,
the stentor's aspect. Other species of Condylostoma
are free, and the only image which we can ascribe to C. auriculata (a picture taken by Jean Marie
Cavanihac from the
Mediterranean shore, see it below) shows a free individual.
according to Fauré-Fremiet 1936, and
Foissner and Wölfl 1994 is most probably a species of Condylostoma,
however Kahl allots a single
nucleus to it. Obviously this species (if it exists) needs to be
newly found and well described. It was found only in 1881 among bryozoa
the aquarium at Westminter.
It is a notable
fact that these two species (at least in the documents that I
could find on the Internet) "disappeared", being quoted neither as Stentor, nor
nor as Condylostoma.
prob. auriculata - pictures
from Marseilles, France, on the Mediterranean shore by Jean Marie Cavanihac. I
believe that this is the only available picture of this
species and the first
citation for the Mediterranean.
Large body, generally with ovoid
shape with a truncated former end. More or less flat body; a large and
visible AZM, in the left edge* of the peristome, spiralling into
somatic cilia. A contractile posterior vacuole
Included here is Fabrea Henneguy 1910, a genus found in brackish water
(up to 20% of salinity), often found in saltworks, and Climacostomum,
from fresh and
brackish waters. Species
of the two genera are relatively small (around 300 microns).
Image of Fabrea salina HTTP
Image of Climacostomum httm//mtlab.biol.tsukuba.ac.jp/www/PDB/Images/Ciliophora/Climacostomum/sp_1.jpg
Form of long reversed cone
(shaped as a "trumpet") adhesive
posterior end, with one Adoral Zone of
Membranelles forming a spiral around one vast
and ciliated peristomial bottom.
Anterior contractile vacuole, with thin channels, one with the
the cell and another around the base of the peristome
understand the orientation of a subject in a drawing or a picture, it
necessary to consider how it is presented
with respect to the observer. On this assumption, what is at our
left in the drawing or photograph,
corresponds to the right in the organism. If no special statement is
made it is
assumed that the organism is drawn by the ventral face.
we can go to
the Stentor species key