Spirula

Posthörnchen ( drawing by Carl Chun )

The Posthörnchen ( Spirula Spirula ) belongs to the class of cephalopods and within the group of squid ( Coleoidea ). It is the only one still living representative of a previously larger order Spirulida. The oldest member of the group are known from the Carboniferous period (before about 360 to 300 million years ago ).

Way of life

During the day the Posthörnchen lives at depths 550-1000 m. At night you will find it but also at lesser depths of at least 100 meters. It follows the swarms of zooplankton.

Housing

The Posthörnchen has hidden in the jacket a spiral wound housing ( the cuttlebone ) with non-touching turns, so it 's horn ram in English squid ( " ram's horn squid " ) is called. The housing has a diameter of 2 to 3 cm, and is divided into several chambers, into which gas is contained. The gas in each chamber can be regulated by the animal to a small extent, keeping the animal in a " headstand " floating in the water column. Contrary to popular belief, the body is not used to ascend or descend in the water column. The creature moves quickly with the help of his fins forward and also in the water column up and down. The Posthörnchen has ten arms, two of which are designed to catch the poor.

The case of dead animals are occasionally found in mass quantities to tropical beaches.

Spirula Spirula Mission Beach, National Park, Queensland, Australia 2002

Spirula Spirula Mission Beach, National Park, Queensland, Australia 2002

Fossil representatives

Until recently, the genera Naefia and Groenlandibelus from the Upper Cretaceous as the oldest members of the order were considered. Then, however, new forms were found from the Carboniferous, to be provided by their wall structure unique to the Spirulida. The greatest diversity, however, the group reached the Tertiary. The best known form is Spirulirostra from the Miocene of Europe. It can be found in many clay pits in northern Germany.

System

The systematics of the squid is at the family level is now widely accepted. In contrast, the classification of the major groups within the squid is so far still not stable. Jereb and Roper the Posthörnchen in their monograph published in 2005, again as a family within the Sepiida. However, the fossil representatives of the group is not taken into account. Naef retired in 1922 from a number of families to be provided in the main line of Posthörnchen. From this viewpoint, a higher hierarchy of Posthörnchen is justified.