aquatic organisms, characterized by asexual (vegetative) reproduction, that remain united with the daughter and subsequent generations and form a more or less complex union, or colony. Among colonial plants are various unicellular algae, including blue-green, green, golden-brown, yellow-green, diatomaceous, dinoflagellate, and euglenoid. Depending on the method of formation (reproduction by zoospores or autospores), the colonies are either zoosporic or autosporic.
Colonial animals predominantly include marine invertebrates and lower chordates. Many unicellular animals, or protozoans, are colonial organisms, such as several flagellates, radiolarians, and infusorians. Other colonial invertebrates include many sponges and the majority of coelenterates (including siphonophores). Bryozoans, entoprocts, Rhabdopleura (order Pterobranchia), almost all hydrozoans, many coral polyps and many polypous generations of various scyphozoans are colonial organisms. Synascidiaepyrosomata, salps, and Doliolidae are examples of colonial lower chordates. The extinct graptolites were colonial animals.
Some colonial animals are sessile, such as bryozoans, hydrozoans, coral polyps, and synascidians. These colonies are usually permanently attached to the substrate and have a more or less developed skeleton. Colonial Radiolaria, Siphonophora, Pyrosomata, Doliolidae, and Salpidae, which live in the depths of the sea, are usually semitransparent and lack skeletons.
Many colonial organisms are metagenetic: there is alternation of asexual and sexual generations. Colonial organisms were the intermediate link in the development of multicellular animals from unicellular animals.
D. V. NAUMOV and T. V. SEDOVA