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Plankton make up 95 per cent of ocean life. Christian Sardet's book Plankton - Wonders of the Drifting World explains everything there is to know about the ocean's smallest particles and their importance to all other life on Earth

Plankton: Wonders of the Drifitng World

Plankton include a multitude of organisms from across all domains of life. This mandala depicts more than 200 different kinds of plankton. In the upper part of the mandala are the largest creatures of zooplankton: jellyfish, sphonophores, ctenophores, salps. 

In the centre are a mix of chaetognaths, annelids, mollusks, and crustaceans. Also included are big larvae and juveniles, ranging in size from a few millimetres to several centimetres. The lower part of the mandala shows microscopic organisms (measuring less than 1 mm), mostly single-cell protists: radiolarians, foraminifera, diatoms, and dinoflagellates. 

This microscopic world also includes many multi-cellular organisms, including the embryos and larvae of the animals above. (Note: individual images are not to scale). 

Unicellular Prototists

Precursers of plants and animals 

More than 800 million years ago unicellular organisms made the first steps towards multicellularity and the start of life as we know it. 

Plankton idImage: Christian Sardet 

 

A Variety of Forms: Who is Who?

When looking through a binocular microscope at plantkon collected with nets ranging in mesh size from 20 to 100 microns, we can sort different protists on the basis of size and form. Try to recognize who is who on this page. There are 1 tintinnid, 4 foraminifera, 14 radiolarians, 12 dinoflagellates (including 3 coouples), and 15 diatoms. The large greenish balls are colonies of green algae. Some multicellular organisms of comparable size are also present - a copepod, 3 jellyfish larvae, an annelid larva, an echinoderm, and a sac of copepod embryos.

Plankton id3 

Dinoflagellates

Pyrocystis lunula

The life cycle of this dinoflagellates includes a phase known as the coccoid stage during which cells at different stages of division are contained within the same shell

 Plankton DinoImage: Christian Sardet

Radiolarians

The heart of a cell

Radiolarians are single-celled planktonic protists, classified in two main groups called polycystines and acantharians. Most radiolarians are microscopic, but some species are visible to the naked eye. The central capsule of a radiolarian includes one or more nuclei and a mass of cytoplasm called endoplasm

Plankton4Image: Christian Sardet 

Tintinnids

A ciliate inside its tunic

Among the myriad species of ciliates in the ocean, tintinnids are the most recognizable, and some would say beautiful, due to their distinctive tunics called loricae, a name borrowed from the armour of Roman soldiers. Built with an armature of protein, loricae resemble trumpets, amphoras, or vases, and some are lavishly decorated with particles. This tintinnid, Rhabdonella spiralis, was discovered in 1881 by Hermann Fol, one of the founders of the marine station at Villefranche-sur-Mer

Plankton5Left: The animal occupies the bottom of its lorica Right: The animal has moved up to the opening and deployed its ciliated corolla | Image: John Dolan, CNRS, Observatoire Océanologique de Villefranche-sur-Mer

Copepods 

Variations on a theme

Copepod crustaceans are the most abundant organisms among the zooplankton, numbering more than 14,000 species. These arthtopod range in size from 0.2 to 10 millimetres and occupy nearly all marine and freshwater ecosystems. 

This male Sappharina copepod reflects and diffracts light through tiny plates situated in the epidermal cells covering its surface. Depending on the orientation of the animal, its flat body switches from fully transparent to brightly coloured. Sapphirina are most abundant when their hosts, the salps, proliferate.

Plankton6Image: Sharif Mirshak, Parafilms, Montreal

 

Crustaceans

Claws and camouflage

Phronima sedentaria use two large claws to catch prey and defend themselves. Like the rest of the anmal, these claws can change colour by means of pigmented cells, called chromatophores, located in the cuticle, above powerful muscles. 

When chromatophores are fully spread they appear star-shaped and the whole animal takes on a reddish tint. Powerful muscles are visible inside the claw

Plankton7Image:credit Christian Sardet and Sharif Mirsha

 

Hetropods

The Beautiful, Transparent Atlanta

Atlanta peronii is a common species in the bay of Villefranche-sur-Mer. A heteropod mollusk with a coiled shell, it possesses a flattened foot that serves as a single swimming fin. Here, two Atlanta peronii heteropods hide inside their calcareous shells. A pair of eyes is visible in each. 

Plankton8Image: Christian Sardet

Cephalopods

Chameleons of the sea

This newly hatched Loligo vulgaris squid (measuring 4 to 5 mm) already displays dozens of red and yellow pigment cells (chromatophores) that modulate the colour of its skin 

Plankton9Image: Sharif Mirshak, Parafilms, Montreal

Pyrosomes

A colony of zooids

Pyrosome colonies contain hundreds of identical individual zooids organised in a cylinder open at one end. The zooids' ciliated gill slits are visible in close-up view. These gill slits efficiently filter and concentrate microorganisms that comprise the pyrosome's food. This pyrosome was collected during the Tara Oceans Expedition off the coast of Ecuador 

Plankton10Image: Christian Sardet

 

The Author

Christian Sardet is the founder of the Laboratory of Cell Biology at the Marine Station of Villifranche-sur-mer. He was also the co-founder of the Tara Oceans Expedition and intiator of the Plankton Chronicles project. www.planktonchronicles.org

This stunning book from The University of Chicago Press has hundreds of close-up photographs of the diverse organisms we know as plankton and which make up 95 per cent of ocean life.

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