bilateral symmetry

Examples of bilateral 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.
  • All true animals, except those with radial symmetry, are bilaterally symmetrical.
  • In contrast to radial symmetry, which is best suited for stationary or limited-motion lifestyles, bilateral symmetry allows for streamlined and directional motion.
  • Animals in the phylum Echinodermata (such as sea stars, sand dollars, and sea urchins) display radial symmetry as adults, but their larval stages exhibit bilateral 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 .
  • Bilateral symmetry is found in both land-based and aquatic animals; it enables a high level of mobility.
  • Bilateral symmetry is illustrated in a goat.
  • The sponge is asymmetrical, the sea anemone has radial symmetry, and the goat has 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.
  • These are the only echinoderms that demonstrate "functional" bilateral symmetry as adults because the uniquely-extended oral-aboral axis compels the animal to lie horizontally rather than stand vertically.
  • 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.

• Superphylum Lophotrochozoa

  • These phyla are also bilaterally symmetrical: a longitudinal section will divide them into right and left sides that are symmetrical .
  • Species in this group have bilateral symmetry.

• Rhizaria

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

• Limits on Animal Size and Shape

  • Animals with bilateral symmetry that live in water tend to have a fusiform shape: a tubular shaped body that is tapered at both ends.

• 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 .

• Characteristics of Vertebrates

  • Animals that possess bilateral symmetry can be divided into two groups, protostomes and deuterostomes, based on their patterns of embryonic development.
  • Echinoderms are invertebrate marine animals that have pentaradial symmetry and a spiny body covering; the phylum includes sea stars, sea urchins, and sea cucumbers.

• Phylum Nemertea

  • They show bilateral symmetry and remarkable contractile properties.

• 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.
  • The bilaterally-symmetrical animals are further divided into deuterostomes (including chordates and echinoderms) and two distinct clades of protostomes (including ecdysozoans and lophotrochozoans).