Neocephalopoda

Extant octopus

• Squid ( Coleoidea )
• Ammonites ( Ammonoidea )
• Bactriten ( Bactritoidea )
• Geradhörner ( Ortho Cerato Idea )

The Neukopffüßer ( Neocephalopoda ) are a diverse group of cephalopods ( Cephalopoda ), which includes the present-day squid ( Coleoidea ), and the † ammonites ( Ammon horns, Ammonoidea ), the † Bactriten ( Bactritoidea ) and some groups of † Geradhörner ( Ortho Cerato Idea ).

The first certain representatives of Neukopffüßer known from the Ordovician. From the oldest cephalopods ( from the Upper Cambrian ) no early stages of housing are known; that is, that you have any evidence for early development. However, these are " traditionally " made ​​to the Altkopffüßern; However, with no real evidence. It is considered the sister group of the Altkopffüßer ( Palcephalopoda ). The classification of the cephalopods ( Cephalopoda ) in Altkopffüßer and Neukopffüßer reflects the phylogeny of modern cephalopods, in which many kinds of inner -shell squid ( Coleoidea ) the few species of nautilus ( Nautilus genera and Allonautilus ) face, ie Represent sister groups. The inclusion of many fossil groups in these two groups would be the concept of nautilus ( Nautilus genera and Allonautilus ) and the Cuttlefish ( Coleoidea ) completely blow up. Therefore Lehmann & Hillmer (1980 ) proposed the classification of cephalopods in Palcephalopoda ( "Nautilus / Allonautilus - line " = Altkopffüßer ) and Neocephalopoda ( " Coleoidea - line " = Neukopffüßer ) before each involving the fossil groups. The inclusion of the Ammonites ( Ammonoidea ) in the Neukopffüßer by U. Lehmann was also by the finds of remains of the rasping tongue ( radula ) with the Ammonites. It has 9 elements per transverse row, making it the rasp of cuttlefish similar; In contrast to the rasp of the nautilus, which has 13 elements per transverse row.

Characterization

The Neukopffüßer ( Neocephalopoda ) are characterized by a moderate compared to the Altkopffüßern yolk- rich development. The hatchlings are or were usually only a few millimeters in size. Compared to most other groups of molluscs ( Mollusca ) is also developing the Neukopffüßer be called yolk- rich, and individual development is direct, ie without larval stage. Another criterion is the Neukopffüßer of mineralization mode of the first housing formed still in the egg. The first case is organically created and then total mineralized. This is done by incorporating the mineral aragonite in the form of prismatic structures. The further growth of the housing after hatching from the egg membrane is accomplished by growth on the front edge of the housing. Thus, the Embryonalgehäuse rises from by slightly different color ( in good condition ) and the absence of any growth lines of the later youth housing. Is usually more or less clear cut off from the second chamber. The Siphonalstrang is thin and mostly organic. From the Neukopffüßern However, groups have repeatedly formed again, who in turn secondarily developed an extremely rich yolk development (such as cuttlefish, some Tiefseeoctopoden, † Arionoceratidae ). Scant remains of Raspelzungen at the Neukopffüßern suggest that they have a rasp with 9 elements per transverse row had (like squid). One older synonym of Neocephalopoda is Angusteradulata Lehmann, 1967.

System

The basal Kopffüßergruppe, the † Ellesmeroceratoidea is, traditionally made to the Altkopffüßern. However, there are as yet no intact early stages become known, and the early individual development of this group is therefore unknown. Due to the development tendency is however to be expected that individual development was only moderately rich in yolk and this group may be counted among the Neukopffüßern. The Neukopffüßer would then be a paraphyletic grouping and group stages.

• Altkopffüßer ( Palcephalopoda )
• Neukopffüßer ( Neocephalopoda ) † Bactriten ( Bactritoidea ) ( core group of ammonites and squid)
• † ammonites ( Ammonoidea )
• Squid ( Coleoidea )
• † Geradhörner ( Ortho Cerato Idea ) ( core group of Bactriten and other groups)