That unit regarding the Mollusca including the bivalve shells, just like the clams and oysters; -- so called since they have no evident head. Formerly the team included the Tunicata, Brachiopoda, and quite often the Bryozoa. See mollusca.
a phrase introduced by Cuvier into organized zoölogy, and applied by him as a class title to a combination of the conchiferous lamellibranchiate mollusks therefore the tunicates.
Just Like Acrania.
In Latreille's system of category (1795), among seven sales of this Linnean Aptera, containing the spiders, etc., matching on Arachnides palpistes of Lamarck, and synonymous with Arachnida.
In Haeckel's category, a group of Mollusca made up of the Spirobranchia, or Brachiopoda, together with Lamellibranchia.