protostome

Examples of protostome in the following topics:

• Superphylum Lophotrochozoa

  • The Lophotrochozoa are protostomes possessing a blastopore, an early form of a mouth; they include the trochozoans and the lophophorata.
  • Animals belonging to superphylum Lophotrochozoa are protostomes: the blastopore (or the point of involution of the ectoderm or outer germ layer) becomes the mouth opening to the alimentary canal.
  • This layer multiplies into a band which then splits internally to form the coelom; this protostomic coelom is termed schizocoelom.

• Animal Characterization Based on Features of Embryological Development

  • These two groups are separated based on which opening of the digestive cavity develops first: mouth (protostomes) or anus (deuterostomes) .
  • The word protostome comes from the Greek word meaning "mouth first. " The protostomes include arthropods, mollusks, and annelids.
  • Protostomes also undergo determinate cleavage: the developmental fate of each embryonic cell is pre-determined.
  • Unlike protostomes, deuterostomes undergo indeterminate cleavage: cells remain undifferentiated until a later developmental stage.
  • In protostomes, part of the mesoderm separates to form the coelom in a process called schizocoely.

• Molecular Analyses and Modern Phylogenetic Trees

  • Extensive molecular analysis using rRNA data found these animals to be protostomes, more closely related to annelids and mollusks.
  • This discovery allowed for the distinction of the protostome clade: the lophotrochozoans.
  • Some scientists believe that the phyla Platyhelminthes and Rotifera within this group should actually belong to their own group of protostomes termed Platyzoa.
  • These two clades now make up the protostomes.

• Constructing an Animal Phylogenetic Tree

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

• Phylum Annelida

  • Annelids show protostomic development in embryonic stages and are often called "segmented worms" due to their key characteristic of metamerism, or true segmentation.

• Phylum Arthropoda

  • Arthropods are eucoelomate, protostomic organisms.

• Characteristics of Vertebrates

  • Animals that possess bilateral symmetry can be divided into two groups, protostomes and deuterostomes, based on their patterns of embryonic development.