Die Embryonalentwicklung der Paradiesschnecke ... - TOBIAS-lib

Kapitel 1
internal solid circular structure in the ventral part of the visceral sac, right
at the position of the invaginated ectodermal tissue that has been formed
the shell gland (Fig. 5a). Starting from this solid structure, with increasing
age the snails developed an internal calcareous shell in the shape of a hollow,
nonsegmented cone, which surrounds the hepatopancreas in its ventralmost
part (Fig. 5).
The phenomenon of Pt-induced body plan changes is not restricted to M.
cornuarietis but could also be observed in embryos of the pulmonate snail
P. corneus exposed to nominal concentrations of ≥ 300 µg/L PtCl 2 from
fertilization until hatch. Also shell-less P. corneus did not form a mantle
cavity (Fig. 3b). In contrast to M. cornuarietis, the longevity of unshelled
P. corneus was restricted to a maximum of about 2 weeks postfertilization.
Discussion
The present study describes and investigates artificially induced shell internalization
in Marisa cornuarietis due to Pt exposure, which corresponds with
fundamental body plan changes.
In contrast to Pt 2+ , the physicochemical similar ion Pd 2+ and other bivalent
metals (Zn 2+ , Ni 2+ , Cd 2+ ; Schirling et al., 2006; Sawasdee and Köhler,
2009) did not interfere with shell formation during embryogenesis. Only occasionally
high concentrations of Li + (2.5 and 3 mg/L LiCl2), a metal which
has been shown to interact with the positional system of predominantly ectodermal
tissue in Xenopus and Loligo (Kao et al., 1986; Crawford, 2003),
prevented the formation of an external shell in M. cornuarietis. So far, solely
the heavy metal Pt seems to specifically interact with key processes during
early embryonic development, which inhibits the mantle to evaginate and to
overgrow the visceral sac, hence, leading to the growth of an internal shell
as it could be traced by the staining of the mantle edge.
Pulse experiments revealed days 4 and 5 postfertilization to be most susceptible
to Pt action on shell formation. Data probably varied due to slight
variation in culture temperature (26 ± 1 ◦ C) and depending on the exact
time of fertilization during the night. During these days of embryonic de-
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