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Giorgio Carboni, March 2000
Translation edited by Giselle Walker

Haematococcus pluvialis CONTENTS



On this page we'll survey 38 movies of bacteria, protists and freshwater multicellular organisms. These movies were made with a simple digital video camera, placed on a compound light microscope.



When you look down the microscope, you often meet bacteria. They are unicellular prokaryotes. Usually, they are much smaller than protists. They are often hardly visible down the light microscope. They come in different shapes: coccus (spherical), bacillus (stick shaped), and spirochaete (helicoidal). Some of them are immobile, others move all the time. Bacteria often feed on dead protists. (Dimension of the window = about 125 x 90 Ám).


This is a very mobile bacterium, probably a Flexibacter. It is shaped like a contorted wire. Above it, you can see a little diatom and under it a green alga.


Blue-green algae are eubacteria that can perform photosynthesis. They are also called Cyanophyceae. They were probably the first organisms on Earth able to produce nutrients to feed themselves. They originated over 3.8 billion years ago. Often their color is blue - green (cyan). Sometimes they are surrounded by a mucous envelope.


This group forms necklaces of spheroidal, ovoidal or cylindrical cells, according to the species. They slide slowly. [See  for other pictures of blue-green algae].


This is a blue-green spheroidal alga. After division, the cells often stay united (up to a maximum of 4 cells) for a certain period of time. In the movie it is surrounded by smaller coccoid green algae.


Blue-green filamentous alga, forming necklaces of oblong cells. Blue-green clear color.



The organisms described from here on are eukaryotic. Euglenids have one or more often two flagella. Often they also have a photosensitive red spot called a stigma. A lot of flagellate algae live individually, though some live in colonies.


This has two flagella, one of which is directed forward, and the other is longer and is dragged by the protist. Even though it is in the same family as many algae, it doesn't produce food by itself, but it feeds on substances it collects in the environment (heterotrophic feeding).


This has only a single flagellum directed forward, which is mobile at its end. Heterotrophic feeding.


Flat heart-shaped flagellate. It has a short and oblique spike on its tail. The stigma is close to the flagellum. Autotrophic (makes food for itself).



Green Algae or Chlorophyta can have many shapes: flagellate, coccoid, filamentous, thallus, etc. They are thought to be the starting point of the "higher" plants, with whom they share many forms of cellular organisation and substances. More than 8000 species of green algae are known. The flagellated forms often have a stigma.


Colonial flagellate alga which forms a small carpet. We see a group of eight cells here, but normally there are sixteen. Every cell has two long flagella. The colony stops sometimes, then starts swimming again.


The name of this protist indicates that it is the color of blood and that its shape is spherical. When this alga is unhappy, it fixes itself to the bottom of its environment and takes the red color due to the abundance of carotenoids. It lives both in clear and clean waters like springs and in puddles of rain water. It has two flagella of equal length, but which are endowed with independent movement and which make the cell tremble as it moves. The cell is placed inside a rigid, transparent and colorless theca, to which is attached with strips of cytoplasm.
[See  for other information on haematococcus.]

Pediastrum simplex

Little colony of green algae with the shape of a small indented wheel. Its peripheral cells are sharpened.


Green alga with pointed extremities. It forms little colonies of 4-8 individuals, slightly staggered. There are many similar species which are hard to identify.



Conjugate algae (Zygnematophyceae) is a class of green algae. The term of conjugate comes from their particular way of sexed reproduction, in which two sexually different amoeboid cells fuse. Conjugates also have asexual reproduction. They are very beautiful algae. They live only in freshwater and have no flagellate stage. Between them, Desmids have cells formed by two symmetrical halves, separated by a deep incision.


The shape of this alga is that of a lunar sickle. (Phase contrast).


Simple desmid. (Phase contrast).


This filamentous green alga is composed of cylindrical cells arranged the one following the other to form unbranched filaments. Their chloroplasts are ribbon shaped and arranged in a helix. The helix of the chloroplast differs according to the species. (Phase contrast).



Diatoms are unicellular algae in a siliceous box formed by two hulls or thecae, the upper of which is bigger and covers the lower one like the cover of a box. The cell lives inside the box. These cases are covered in minuscule holes, incisions and reliefs arranged in regular patterns to form attractive grids. The variety and the beauty of their forms is so great that there are enthusiasts exclusively devoted to the collection and the study of diatoms. The system of locomotion of these algae is special. The lower hull has some holes in it and a longitudinal fissure, named a raphe. Part of the cell's cytoplasm escapes from this crack and produces a sticky secretion which flows along the raphe, allowing the diatom to move as though it were on tracks. Diatoms appeared about 135 million years ago.

Diatom 1

Diatom with clear chloroplasts and little oil drops.

Diatom 2

Diatom which skirts a spirogyra.

[   Some beautiful images of diatom hulls.]



True amoebae belong to the the class Rhizopoda (Protista). They emit temporary mobile appendages, called pseudopodia, through which they can move and also phagocytose particles. Also belonging to this group of protean organisms, are Thecamoebae (amoebae with protective shells), and Foraminifera, marine organisms and with a calcareous shell.

Amoeba 1

Amoeba cells continuously change form. Unlike some other rhizopods, they have only a thin membrane (no shell). There are numerous kinds of amoebae, which differ in shape, dimensions and movement of the pseudopodia. Amoeboid movement is particularly curious and fascinating. Inside amoebae you can also see ingested prey and contractile vacuoles. (Phase contrast).

Amoeba 2

Amoeba phagocyting another protist. Observe the variation of the shape of the outline of the amoeba during phagocytosis.



Ciliates form one of the richest and varied communities of aquatic microorganisms. Their name come from the fact they possess cilia, which can move individually, or together as cirri (several bundled together) or as membranelles (rows) or as kineties (coordinated rows forming a grid). The ciliate cell is often very complex. It has defense organs (trichocysts), digestive vacuoles, contractile vacuoles and a lot of other organelles that make these organisms very versatile. Ciliates feed on bacteria, other protists, rotifers and random floor particles.


Two Aspidisca are exploring filaments of spirogyra and other filamentous algae looking for bacteria.


Two ciliates are looking for food, (bacteria and organic detritus). Notice how they use their ventral cilia to move on the debris.


Cinetochilum is similar to Euplotes both in its movement and in its shape. However it is smaller, more oval and has dorsal ribbings.


Coleps is entirely covered with cilia. The cell has longitudinal and horizontal ribbings which make it similar to a barrel. They are often found in groups swimming around debris. At the back end of this ciliate there are some characteristic short points.


Euplotes walks on algae using its cirri (cilia fused together) individually. It is even able to swim. Its versatility is an indication of the complexity of its cell.


This is a large, active ciliate. Its two proboscis incessantly explore the surrounding environment looking for bacteria and organic detritus. They have a long buccal (mouth) fissure.


Oxytricha is a flat ciliate of remarkable size (130 Ám about), entirely covered in cilia. As with Euplotes, on its abdominal side, some of these cilia are fused in cirri which the protist can move either together or individually. So it manages both to swim and to walk. It collects a lot of water and expels it by means of a contractile vacuole.


Paramecium is probably the best known protists even by those who do not have a microscope. It looks like a slipper. It feeds on bacteria and lives in waters quite rich in organic substances.


You can easily recognize the Stentor by its trumpet like form. Its oral aperture or peristome is provided by a membranelle which draws alimentary particles. Sometimes it swims freely, other times it remains anchored to the bottom. It can attain the length of  some millimeters and this makes it one of the biggest protozoa. Like the Paramecium, the Stentor lives in waters rich of bacteria and of organic detritus.

Trichodina (low power)

These are ciliates which live on the bodies of little aquatic animals. In this case, they live on a green hydra. They are those small clear suckers which move on the along the body of the hydra. They have a form of sucker and a ciliary apparatus similar to that of Vorticella. Sometimes they stand up, other times they quickly move along the body of the host. They sometimes seem to quarrel with each other and at times some leave the host, swimming freely in the water, eventually landing in a new position, or above a companion.

Trichodina (high power)

As above, but at a higher magnification. (The diameter of these protists is 35-60 Ám, while the diameter of the body of the hydra is about 0.2 mm).


Vorticella is a unicellular bell-shaped ciliate. It is attached to the bottom by means of a retractile stalk. On the edge of the bell there is a crown of cilia or peristomium which beatbeats to create a vortex in the water. The heaviest particles are dragged into the oral opening of the vorticella, and if they are of the proper dimensions, they are ingested. This vorticella is accompanied by a half hidden companion. Inside the vorticella you can see green corpuscles. There are algae ingested and which are in the process of being digested. A lot of species of vorticella are colonial. Some species are green colored because inside them they host little unicellular algae, with whom they exchange nutrients.



Water Snail Embryo

In this movie you can see an embryo of Physa acuta, a freshwater snail. It is inside an ovoidal space around 0,8 mm long. This space contains liquid and it is surrounded by a gelatinous substance used in defense, hindering any raiders that try to reach the eggs. In a brood of these aquatic snails there are some dozen eggs.


Fillipods are small freshwater crustaceans usually called water fleas or Daphnia. Their body is contained between two hemispherical carapaces from which only head and legs emerge. They use their antennae to swim and their legs for filtering water and capturing food. They feed on plankton and in turn are preyed upon by fish.

Hydra attenuata

Hydra are minuscule aquatic polyps a few millimeters long, related to jellyfish. Their body has a structure like a sack and is made of only two layers of cells. The tentacles depart from around the oral opening. They possess stinging cells used to capture prey. In general they reproduce by budding. Normally hydra are fixed to the bottom by a foot, but they are also able to walk with movements like a compass, or turning somersaults. (Diameter of the body = 0,2 mms).

Hydra viridis

Inside the Hydra viridis or green hydra there are many algae which live in symbiosis with the polyp. It seems that this species of hydra sometimes feeds directly on these algae, digesting some of them. Notice the hydra daughter, born by gemmation from the body of its mother.

Larva of Dytiscus

The larva of Dytiscus is a ferocious predator. It attacks tadpoles, small fish and other larvae. It feeds on its siblings so that often only a single individual remains from a whole brood. The larva introduces a proteolytic liquid into the body of the victim and then sucks the victim's denatured proteins through canaliculae present in its jaws. In the movie a larva opens its jaws (not to their full width).


Rotifers almost exclusively live in freshwater. They are from 40 Ám to 3 mm long. The biggest species are formed by about 1000 cells and they live for a week. On their head they have some cilia which beat to produce a vortex. In this way particles of food and microorganisms on which the animal feeds are attracted. Below the head, you can see the mastax, the chewing (masticatory) apparatus typical of rotifers. (Length of this animal = about 100 Ám). There exist about 2000 very diverse kinds of rotifer.

Rotifer (higher magnification)

In this movie, you can see the same rotifer as before, but with a higher magnification. Starting from the foot, formed by two appendages, you can observe the bowel (orange) and the stomach full of green algae, then the mastax and then the rotatory apparatus.

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