Ernst Haeckel, Adolf Giltsch
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Cytherea. / Acephala. – Muscheln.

Lithograph by Ernst Haeckel and Adolf Giltsch

Plate 55 from Kunstformen der Natur.
This is one of the 100 pop science biology illustrations that were published from 1899 – 1904 in Leipzig by Ernst Haeckel through Verlag des Bibliographischen Instituts.

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Translation of the original German introduction by Ernst Haeckel:

The class of Acephala is distinguished from the other Mollusca by two most characteristic peculiarities: regression of the head (therefore ‘headless’, Acephala), and the two-flapped shell formation (therefore ‘two-flapped’, Bivalva). Usually, the soft body of the Acephala is fully hidden inside the shell cavity or “Conchylia” and, in case the shell closes, completely sealed off from the outside world. The closing mechanism of the shell is achieved by contraction of one or two strong muscles that transverse the body laterally and bring closer both flaps until the rims (at the abdominal side) interlock. The opening of the shell (when releasing the muscular traction) however is effected with the help of a strong elastic band (‘closing band’ or ligament) that runs along the central line of the dorsum. As soon as one inserts a knife in between the two shell flaps of a closed oyster and intersects the closing ligament the flaps separate strikingly due to the elasticity of the ligament on the ventral side (fig. 11). Both flaps that cover and protect right and left side of the Acephala, together with the ligament that connects them, form three parts of an originally simple shell-shaped dorsal cover; trisection occurred with the formation of two parallel longitudinal furrows.
The shell of Acephala is just like the shell in snails (plate 53) and in octopuses (plate 44) the solidified and calcareous discharge product of the mantle, a thin cutaneous fold, raising from the back of the animal and hanging down to the right and left in the form of two thin lopes. In between these two ‘mantle-lopes’ and the actual pouch-shaped body of the animal one or two pairs of large leaf-shaped gills are hanging (therefore the common name “leaf-gilled”, Lamellibranchia).

Translation by VR Translators Bangalore

We've scanned the original lithography at 1200dpi on the Epson A3 scanner of A3 scanner huren. You can download a 400dpi JPEG here.