BIOL0012

• What are metazoans?

  Motile, multicellular, eukaryotic organisms
• What is the first identified Metazoan animal?

  Dickinsonia
• What stage do metazoans go through during development?

  The blastula stage
• What did lipid biomarkers from Dickinsonia reveal?

  Produced cholesteroids, a hallmark of animals
• Why was it difficult to distinguish dickinsoniids from protists?

  Absence of mouth, gut, and bilateral symmetry
• What are hydrocarbon biomarkers?

  Molecular fossils of lipids and biological compounds
• How do Dickinsonia's sterol compositions compare to lichens?

  Unlike lichens, consistent with animal sterol production
• What percentage of Dickinsonia's sterols are cholesteroids?

  At least 99.7%
• What do most animals produce exclusively?

  C27 sterols (cholesterol)
• What does the presence of cholesteroids in Dickinsonia suggest?

  Classification within the animal kingdom
• What are the characteristics of bilaterians?

  • Bilateral symmetry
  • Triploblastic
  • Cephalization (organs and nerve tissues at the front)
• What are non-bilaterian metazoans called?

  Radiata
• What are the key phylums of Radiata?

  Cnidaria, Placozoa, Porifera, Ctenophora
• What is the traditional view of radiata phylogeny?

  Porifera is the sister group to all animals
• Why do sponges (Porifera) lack epithelium?

  They lack structures to maintain a controlled environment
• What is the non-traditional view of radiata phylogeny?

  Ctenophora is the sister group to all animals
• What is the argument for ctenophores being basal?

  Ctenophores lack essential genes for nervous system
• What traits do ctenophores possess?

  True epithelia, nervous systems, muscles, and guts
• What is needed to resolve the debate on ctenophores' phylogeny?

  Methodological consensus among researchers
• What are the main divisions of Bilateria?

  • Protostomes
  • Spiral cleavage
  • Blastopore becomes mouth
  • Deuterostomes
  • Radial cleavage
  • Blastopore becomes anus
• What are protostomes characterized by?

  Spiral cleavage and mouth from blastopore
• What do deuterostomes have regarding cleavage?

  Radial cleavage
• What is debated about Xenacoelomorpha?

  Whether they are deuterostomes
• What are the major arthropod lineages mentioned?

  Hexapod, Myriapod, and Crustaceans
• What is the defining feature of the clade Tracheata?

  Presence of a tracheal system for breathing
• What is Pancrustacea also known as?

  Tetraconata
• What is the conserved structure in Pancrustacea's eye compounds?

  Arrangement of ommatidia
• How does the number of cells in the eye structure of millipedes compare to that of Pancrustacea?

  Millipedes have a highly variable number of cells
• What supports the Pancrustacea clade according to molecular data?

  Neuroanatomical similarities and molecular analyses
• What classification do insects fall under?

  Crustaceans
• What do the shared characters between crustaceans and hexapods indicate?

  They are homologous traits
• What does Mandibulata unite?

  Myriapods, crustaceans, and hexapods
• What has challenged the Mandibulata grouping?

  Paradoxopoda: myriapods with chelicerates
• What do robust analyses suggest about Mandibulata versus Paradoxopoda?

  Mandibulata is favored when excluding fast-evolving genes
• What is the significance of the Dachshund gene in Mandibulata?


  It defines the tip and base of appendages
• What do localized patterns of gene expression indicate in Mandibulata?

  Specialization and homologous structures
• How do fossils help in phylogenetics?

  They identify where traits evolve in lineages
• What is a crown group based on?

  Living diversity of species
• What is a stem group used for in phylogenetics?

  To study evolution of common ancestors
• What do Martissonia's fossils reveal about arthropod evolution?

  Transformation of limbs into feeding appendages