Vibrio (Mull), the type of the vibrionia, a family of minute colorless organisms, arranged by Ehrenberg and Dujardin among infusorial animals from the possession of apparently voluntary motions, but now generally considered as microscopic plants, compound or confervoid algae of the tribe oscillatoriaceoe. They are exceedingly minute, requiring the highest powers of the microscope to make out any structure; they appear like slender lines, straight or sinuous, composed of minute joints, without any visible organs of motion, though possessing contractility; they seem to be propagated by the formation of new joints and subsequent separation at one of the articulations; their structure is best seen when dried. They appear suddenly in artificial infusions, and grow rapidly in such immense numbers as to form a thick scum on the surface; they are also found in the tartar on the teeth, in purulent discharges, and in other morbid fluids. The species of the genus vibrio have an undulatory and sinuous motion, like a serpent; in spirulina, which is coiled in a long spiral, the movements are gyratory and oscillating.

In vibrio there is a single, straight row of filaments, without apparent sheath; V. subtilis, about 1/430 of an inch long and 1/24 wide, is aquatic and found in pools; some of the other species are probably the earlier stages of other unknown algae. - The so-called "eels" of vinegar and sour paste, sometimes erroneously styled vibrios, are nematoid worms or entozoa; they were once popular microscopic objects. They belong to the genus anguillula (Miill.); the A. aceti or vinegar eel is 1/30 to 1/17 of an inch long, and the A. glutinis or paste worm 1/15 of an inch; their absence in vinegar is due to the freedom from mucilage and the usual addition of a little sulphuric acid.