The aculifera (Aculifera, synonym Amphineura) include within the mollusks (Mollusca) the groups of aplacophora (Aplacophora) consisting of the Schildfüßern (Caudofoveata) and the Furchenfüßern (Solenogastres) and the Chitons (Polyplacophora).
This group is justified by the lack or replacement of the mollusc shell by calcium deposits in the outer skin. In the case of worm mollusks, these are calcified needles, so-called spicules. The beetle snails have a chalky shell, which consists of a total of 8 limestone plates, which rests on the back of the animals. Further apomorphies of the group are the subterminal anus and a nerve ring around the anus.
The aculifera are contrasted with the group of shell molluscs (Conchifera):
This group formation is opposed to another theory, which regards the Aculifera as an unnatural group (Paraphylum). In this theory, the Solenogastres together with all other mollusks form the sister group of the Caudofoveata and the Polyplacophora with the remaining mollusks form the sister group to the Solenogastres:
Molluscs (mollusca)
NN
Solenogastres
NN
Beetle snails (Polyplacophora)
Conchifera (specified above)
Caudofoveata
The theory that the worm mollusks are the sister group of all other mollusc groups has already been put forward.
Molluscs (mollusca)
Worm mollusks (Aplacophora)
Shield-footed (Caudovoveata)
Furefoots (Solenogastres)
Eumollusca or Testaria
Beetle snails (Polyplacophora)
Shell molluscs (Conchifera)
literature
Klaus-Jürgen Götting: Aculifera, prickly molluscs In: Westheide, Rieger (Hrsg.): Special Zoology Part 1: Protozoa and invertebrates. Gustav Fischer Verlag, Stuttgart, Jena 1997; Pages 284ff.
