radial symmetry

Examples of radial symmetry in the following topics:

• Animal Characterization Based on Body Symmetry

  • Animals can be classified by three types of body plan symmetry: radial symmetry, bilateral symmetry, and asymmetry.
  • Radial symmetry is the arrangement of body parts around a central axis, like rays on a sun or pieces in a pie.
  • All true animals, except those with radial symmetry, are bilaterally symmetrical.
  • This is termed secondary radial symmetry.
  • The larvae of echinoderms (sea stars, sand dollars, and sea urchins) have bilateral symmetry as larvae, but develop radial symmetry as full adults.

• Body Plans

  • Animal body plans can have varying degrees of symmetry and can be described as asymmetrical, bilateral, or radial.
  • They can be asymmetrical, radial, or bilateral in form .
  • Radial symmetry describes an animal with an up-and-down orientation: any plane cut along its longitudinal axis through the organism produces equal halves, but not a definite right or left side.
  • Bilateral symmetry is illustrated in a goat.
  • The sponge is asymmetrical, the sea anemone has radial symmetry, and the goat has bilateral symmetry.

• Constructing an Animal Phylogenetic Tree

  • Eumetazoa are subdivided into radially-symmetrical animals and bilaterally-symmetrical animals and are classified into clade Radiata or Bilateria, respectively.
  • The cnidarians and ctenophores are animal phyla with true radial symmetry.

• Rhizaria

  • A second subtype of Rhizaria, the radiolarians, exhibit intricate exteriors of glassy silica with radial or bilateral symmetry .

• Classes of Echinoderms

  • Of all echinoderms, the Ophiuroidea may have the strongest tendency toward 5-segment radial (pentaradial) symmetry.
  • Their early larvae have bilateral symmetry, but they develop fivefold symmetry as they mature.
  • Several sea urchins, however, including the sand dollars, are oval in shape, with distinct front and rear ends, giving them a degree of bilateral symmetry.
  • Although the basic echinoderm pattern of fivefold symmetry can be recognized, most crinoids have many more than five arms.
  • Sea cucumbers are the only echinoderms that demonstrate "functional" bilateral symmetry as adults, as they lie horizontally as opposed to the vertical axis of other echinoderms.

• Phylum Cnidaria

  • Phylum Cnidaria includes animals that show radial or biradial symmetry and are diploblastic: they develop from two embryonic layers.

• Phylum Echinodermata

  • Echinoderms are invertebrates that have pentaradial symmetry, a spiny skin, a water vascular system, and a simple nervous system.
  • Adult echinoderms exhibit pentaradial symmetry and have a calcareous endoskeleton made of ossicles, although the early larval stages of all echinoderms have bilateral symmetry .
  • Echinoderms possess a unique ambulacral or water vascular system, consisting of a central ring canal and radial canals that extend along each arm .
  • The ring canal connects the radial canals (there are five in a pentaradial animal), and the radial canals move water into the ampullae, which have tube feet through which the water moves.
  • The nervous system in these animals is a relatively simple structure with a nerve ring at the center and five radial nerves extending outward along the arms.

• Class Scyphozoa

  • In some species, the digestive system may be further branched into radial canals.

• Animal Characterization Based on Features of Embryological Development

  • Radially-symmetrical animals are diploblasts, developing two germ layers: an inner layer (endoderm) and an outer layer (ectoderm).
  • Deuterostomes undergo radial cleavage where the cleavage axes are either parallel or perpendicular to the polar axis, resulting in the alignment of the cells between the two poles.

• Vertebrate Axis Formation

  • Mutations in these genes leads to the loss of symmetry required for organism development.
  • Animal bodies have three axes for symmetry: anterior/posterior (front/behind), dorsal/ventral (back/belly), and lateral/medial (side/middle).