Biology: Development and Circulatory System

Closed Circulatory System

• Blood moves continuously through vessels separated from body fluids

Patterns of Development

• The basic Bilaterian pattern of development involves:
  • Mitotic cell divisions (cleavage) of the egg forming a hollow ball of cells (blastula)
  • Blastula indents to form a two-layer-thick ball with:
    • Blastopore (opening to the outside)
    • Archenteron (primitive body cavity)

Evolution of Development

• Bilaterians can be divided into two groups:
  • Protostomes: develop the mouth first from or near the blastopore
  • Deuterostomes: develop the anus first from the blastopore, and the mouth develops later from another region of the embryo

Differences between Protostomes and Deuterostomes

• Cleavage pattern of embryonic cells:
  • Protostomes: spiral cleavage, new cells form to the right or left of previous cells
  • Deuterostomes: radial cleavage, new cells form on top of previous cells
• Developmental fate of cells:
  • Protostomes: determinate development, cell fate is determined early
  • Deuterostomes: indeterminate development, cell fate is not determined until after several divisions
• Formation of the coelom:
  • Protostomes: cells move apart to form coelom
  • Deuterostomes: groups of cells pouch off to form coelom

Segmentation

• Evolution of segmentation provides two advantages:
  • Allows for redundant organ systems in adults, such as in annelids
  • Allows for more efficient and flexible movement, as each segment can move independently
• Segmentation appeared several times in animal evolution

Animal Phylogeny

• Traditional animal phylogeny was developed from morphological, molecular, life history, and other types of relevant data
• New phylogenies are constructed from molecular data, which may suggest different phylogenetic relationships
• Current phylogeny shares common ground with traditional phylogeny, but some parts are not firmly established

Classification of Animals

• Multicellular animals are divided into distinct phyla
• Animals are divided into two main branches:
  • Porifera (Sponges): Parazoa - monophyletic
  • Eumetazoa: Animals other than sponges
• Phylum Cnidaria branches off the evolutionary tree before Bilateria
• Phylum Bilateria includes deuterostomes and protostomes

Protostome Divisions

• Protostomes are divided into:
  • Spiralians: grow by gradual addition to the body mass, have spiral cleavage, and include two main groups:
    • Lophotrochozoa
    • Platyzoa
  • Ecdysozoans: animals that molt, including arthropods and many other phyla

This quiz covers the basics of the closed circulatory system and patterns of development in bilaterians, including cell divisions, blastula formation, and body cavity development.