Bilateria

The Bilateria are animals which are bilaterally symmetrical. They have front and a back end, an upside and downside, and a left and right side. Most animals are bilateral.

Bilateria Temporal range: Ediacaran – Recent
Diversity of bilaterians.
Scientific classification
Kingdom:	Animalia
Clade:	ParaHoxozoa
Clade:	Bilateria

Main subgroups

• Deuterostomia
  • Echinodermata (20,000 species, 7000 living)
  • Chordata. mostly Vertebrata (63,000 species)
  • Hemichordata
• Protostomia
  • Ecdysozoa (6 to 20 million species)
    • Nematoda (20,000 species known +many more)
    • Arthropoda (one to 10 million species)
  • Lophotrochozoa
    • Annelida (17,000 species)
    • Platyhelminthes (20,000+ species)
    • Mollusca (85,000+ species)
    • Brachiopoda (5,000 fossil species)
    • Rhombozoa
  • Platyzoa
  • Minor phyla (like Chaetognatha)

Numbers are approximate; extinct species numbers cannot be known for most phyla.

Bilateria Media

• One view is that the original bilaterian was a marine worm somewhat like Xenoturbella.

• Ikaria wariootia, living 571–539 million years ago, is one of the oldest bilaterians identified.

• Xenoturbella japonica holotype female. The white arrowhead indicates the ring furrow.

• Proporus sp. -Acoela

• 

  Portugal 20140812-DSC01434 (21371237591)

• Blueback herring fish (white background).jpg

  Blueback herring fish (white background)

• Long nosed weevil edit.jpg

  A Long Nosed Weevil, Rhinotia hemistictus, taken in Swifts Creek, Victoria in November 2007

• Grapevinesnail 01.jpg

  Picture of a grapevine snail.

• 

  Xenoturbella japonica holotype female. The white arrowhead indicates the ring furrow.

• 

  Portugal 20140812-DSC01434 (21371237591)

Related pages

• List of animal phyla