SUBCLASS NAUTILOIDEA

• Septa is simple and concave, and produce

  simple sutures
• Siphuncle has septal necks that point to the

  rear (directed backward)
• Predatory, have horny and beak-like jaws
• NAUTILUS SHELL

  The red line is the siphuncle

  
• SIMPLE SEPTA OF NAUTILOIDS VS AMMONITE SEPTA

  • Ammonoids are an extinct group of molluscs thought to be more closely related to coleoids than they are to nautiloids.
• SIMPLE SEPTA OF NAUTILOIDS VS AMMONITE SEPTA

  • Nautiloids have simple septa while ammonoids or ammonites developed septa with intricate folds called lobes and saddles, as well as lacey patterns on the outer shell
• 3 basic patterns for ammonite septa:

  • goniatite (irregular zigzag)
  • Ceratite (regular wavy)
  • ammonite (feathery or fern-like patterns)
• Sutures - patterns of septa can be reflected on the outside of the shell. (complex in ammonoids and complex in nautiloids)
• Sutures in following order (left to right)

  1. Nautiloid
  2. Goniatite
  3. Ceratite
  4. Ammonite

  
• Comparison of NAUTILUS SHELLS in three common species:

  • N. macrophalus (left)
  • Allonautilus scrobiculatus (center)
  • N. pompilius (right) -common