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.

• The Complement System

  • As part of the innate immune system, elements of the complement cascade can be found in species earlier than vertebrates, most recently in the protostome horseshoe crab species, putting the origins of the system back further than was previously thought.

• Characteristics of Vertebrates

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

• 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.