Die Embryonalentwicklung der Paradiesschnecke ... - TOBIAS-lib

Kapitel 2
Fig. 10 7 : Hypothetical change in body axis around which the visceral sac rotates; upper
sketch: control embryo and lower sketch: Pt-exposed embryo.
veloped a mantle nor a mantle cavity. As described, platinum 2+ completely
stopped mantle anlage growth and, thus, also prevented a physical horizontal
rotation of the visceropallium relative to the cephalopodium.
Presuming that the horizontal rotation of the visceral sac in M. cornuarietis
has similar effects on its body plan as the rotation in vetigastropods
and patellogastropods called “torsion”, and following the rotation hypothesis
proposed by Garstang (1929), one would expect our experimentally modified
snails to resemble the hypothetical ancestral mollusc (Page, 1997) and thus
to have a posterior anus. However, this was not the case. On the contrary,
the intestine seemed to be formed just like in embryos from the control group
and the anus in shell-less snails was located at approximately the same position
on the right side of the visceral sac just behind the head. At least the
intestine ended up in a postrotational position even without the event of rotation
itself, that is, the lacking of a horizontal rotation of the visceropallium
by 180 ◦ relative to the cephalopodium, and despite a vertical rotation of the
visceral sac by 90 ◦ .
This was not true for the ctenidium. Without the normal, disproportionate
growth of the mantle epithelium that pushes the epithelium of the right
7 Die Zeichnung wurde von Heinz-R. Köhler angefertigt.
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