Mollusca		Nautiloidea
CYRTOSOMA		Nautiloidea

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Nautiloidea

CYRTOSOMA
|--+--SCAPHOPODA
|  `--CEPHALOPODA
|     |--NAUTILOIDEA
|     |  |--Tarphycerida 
|     |  |  |--Tarphycerina  
|     |  |  `--Barrandeocerina  
|     |  `--Oncocerida 
|     |     |--Oncoceratidae  
|     |     `--Nautilida  
|     |        |--Nautilida i.s.
|     |        `--Nautilina
|     `--NEOCEPHALOPODA
|        |--Ammonoidea
|        `--COLEOIDEA
|           |--DECAPODIFORMES
|           `--VAMPYROPODA
`--Gastropoda

Introduction

Appearing during the Furongian they evolved into a great diversity of forms and lifestyles, as indicated by the amazing range of shell types and structure (see illustration above).  Remaining diverse throughout the early to mid Paleozoic, they declined later in the era, and have remained relatively unimportant ever since.  There are only 3 or 4 living species, all belonging to the single genus Nautilus (the pearly nautilus),

Physiology

graphic fromLake Témiscamingue Fossil Centre

Nautiloids possess of an external shell divided into chambers by walls known as septa. Contact between septa and the shell wall produces suture lines, often visible in fossil forms.  The animal lives in the outermost chamber, called the living chamber.  Nautiloids are distinguished from the very similar Ammonoids by the simple nature of the suture lines, and a siphuncle located usually along the center of the shell.  Key features which are very important in nautiloid classification are the internal and external structure of  siphuncle and the type of internal (cameral and siphuncal) calcareous "ballast" deposits.

Systematics

Despite appearing in text books for many decades, the term Nautiloidea is now considered taxonomically useless.  Many controversies arose which characters can be used for classifying subclasses, orders, families and genera.  Characters were not investigated according to cladistic or phylogenetic relationships, and often were quite arbitrary.  Different researchers came up with totally different classifications.  Generally, Nautiloidea is retained as a general catch-all for all cephalopods that are not ammonoids or coleoids.  However the subclass Nautiloidea does appear to be partially equivalent to the paraphyletic group "Palcephalopoda."

More than 270 families of Nautiloidea are currently known, about 1750 genera, and some 9000 species.  No doubt there are innumerable more waiting to be discovered, or species that never fossilized.

Infraclass Nautiloidea Agasiz, 1947 
Order Tarphycerida Flower, 1950
      Suborder Tarphycerina Flower, 1950
      Suborder Barrandeocerina Flower
Order Oncocerida Flower, 1950
Order Nautilida Agassiz, 1847

Links

The Cephalopod Page - Cool site.  Beautiful photos, well-written and informative text, and heaps of links.  Recommended.  Mostly recent species but there is a page on Ammonites.

Cephalopoda

Old Calamari - Kevin Bylund's site on fossil Cephalopoda. Covers Nautiloids and Ammonoids of Utah (arranged according to geological age), as well including some useful cephalopod and paleontology links.

Cephalopods

All the recent cephalopod shells are composed of aragonitic layers : prismatic layers, nacreous layers and spherulitic prismatic layers.  It must be noticed that the "prismatic" layers in Cephalopod shells are not similar to those of other mollusks ; they are always aragonitic, and composed of small fibres, resembling to the fibres of the coral skeletons.