Rhizopoda

Century Dictionary and Cyclopedia

1. In Dujardin's system of classification (1841), the third family of “diversiform infusorians without visible locomotory appendages”—that is, without permanent appendages, as cilia or flagella. This is the original meaning of the word, since much extended. Dujardin included in his Rhizopoda the 8 genera Arcella, Difflugia, Trinema, Euglypha, Gromia, Miliola, Cristellaria, and Vorticella.
2. The lowest class of Protozoa, composed of simple or multiple animalcules without definite or permanent distinction of external parts, and provided with diversiform temporary or permanent pseudopodial prolongations of the bodysubstance, by means of which locomotion, fixation, and ingestion are effected. There is no mouth or special ingestive area; the sarcode may be distinguishable into an outer ectoplasm and an inner endoplasm; a nucleus and nucleolus (endoplast and endoplastule) may be present; and most of these animalcules secrete a shell or test, often of great beauty and complexity. The rhizopods are minute, usually microscopic organisms, some or other forms of which abound in both salt and fresh waters. The characteristic pseudopodia are highly diverse in form, and constantly change, but occur in two principal forms, coarse lobate or digitate processes and fine slender rays, both of which may run together or interlace. The valuation and limitation of the Rhizopoda have varied with different authors. A normal amœboid protozoan is a characteristic example of this class. Other forms included under Rhizopoda are the so-called moners of the order Monera; the Foraminifera, with a calcareous shell; and the Radiolaria, with a silicious shell. By common consent the sponges, which have been classed with Rhizopoda, are now excluded, even by those who still consider these organisms as protozoans. See cuts under Amœba, Foraminifera, and Radiolaria.

GNU Webster's 1913

1. n. (Zoöl.) An extensive class of Protozoa, including those which have pseudopodia, by means of which they move about and take their food. The principal groups are Lobosa (or Amœbea), Helizoa, Radiolaria, and Foraminifera (or Reticularia). See protozoa.

WordNet 3.0

1. n. creeping protozoans: amoebas and foraminifers