World Congress of Malacology Antwerp ... - Unitas Malacologica

(Herminespina, Muregina, undescribed buccinids). A strong connection with the Southwest Pacific
during the early Miocene of Chile (30% of genera; e.g. Bedeva, Xymene, Xymenella, Penion,
Lamprodomina, Awheaturris, Maoridaphne, Zeacuminia, Marshallena) disappeared later during the
Miocene. Other genera apparently retreated north when water temperatures decreased during the
Miocene and Pliocene (Muregina, Macron, Borsonella, Nihonia). Factors controlling the patterns of
immigration, origination and extinction that created the current Peru-Chile endemic fauna are
discussed as well as regional differences between the two countries.
Effect on burying deep of Mesodesma mactroides by artificial siphon nipping and different
nutritional conditions
Núñez, Jesús 1 ; Porrini, Leonardo 1 ; Penchaszadeh, Pablo E. 2,3 ; Cledón, Maximiliano 1,2
1. Dpto. de Cs Marinas, Facultad de Cs. Exactas y Naturales, Universidad Nacional de Mar del Plata,
Funes 3350, Mar del Plata 7600, Argentina,
Email: bio_jdn@yahoo.com.ar ; leoporra@hotmail.com
2. CONICET, Avda. Rivadavia 1917, CP C1033AAJ, Cdad. de Buenos Aires, Argentina,
Email: mcledon@mdp.edu.ar
3. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Av. Angel Gallardo 490,
C1405DJR, Buenos Aires, Argentina,
Email: penchas@bg.fcen.uba.ar
Siphon nipping is supposed to increase vulnerability to lethal predation but it is not widely proven.
This work aims to prove the effect of siphon nipping and low food availability on Mesodesma
mactroides burying deep. Siphon nipping was simulated by cut of terminal 10% of siphons. Low food
availability was achieved by maintenance of individuals in a closed water recirculation system while
natural food availability was obtained in an open water circulation system whit direct input of
unfiltered sea water pumped directly from the sea. Light and temperature conditions were natural for
both systems. Individual burying deep was measured after 24 hours.
To test the effect of nipping, natural fed clams were compared. Cut individuals were buried 50% less
than uncut (ANOVA p=0.004). The same effect was observed in sub-fed clams (ANOVA p=0.0001).
To test feeding effect, uncut clams were compared. Sub-fed individuals were buried 30% deeper than
the natural fed (ANOVA p= 0.046). No significative effect was observed when cut clams were
compared.
Present results prove that siphon nipping affect burying deep of M. mactroides in a higher proportion
than expected by actual anatomical effect, turning them more vulnerable to lethal predation.
Environmental variables play an important role in determination of burying deep as shown by
phytoplankton availability. The effect of temperature and light remain to be tested. If result does not
change significantly from present ones, these clams would be more vulnerable in spring-summer
season. This could be related to physiological advantages for filter or reproduction when clams are
near the sand surface.
Small fossil gastropods: their meaning for phylogeny and diversity
Nützel, Alexander
Bayerische Staatssammlung für Paläontologie und Geologie, Richard-Wagner-Str. 10, 80333
München, Germany,
Email: a.nuetzel@lrz.uni-muenchen.de
The study of fossil gastropods with small adult size and of protoconchs has revolutionized our view
of gastropod evolution. Protoconch characters increase the total number of shell characters
considerably and therefore they improve phylogenetic analyses and taxonomy. There are spectacular
examples of teleoconch convergence that were resolved by protoconch studies. Except of a few early
pioneer studies, minute gastropod shells including protoconchs have mainly been studied since the
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