World Congress of Malacology Antwerp ... - Unitas Malacologica

ADDENDUM
Feeding mechanism in volutids from north Patagonian shallow waters
Bigatti, Gregorio 1 ; Sanchez Antelo, Carlos J.M. 2 ; Penchaszadeh, Pablo E. 2
1 Centro Nacional Patagónico CENPAT – CONICET, Bvd. Brown s/n., U9120ACV Puerto Madryn,
Chubut, Argentina,
Email: gbigatti@cenpat.edu.ar
2 Depto. de Biodiversidad, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires,
Argentina.
The volutids Odontocymbiola magellanica (Subfamily Odontocymbiolinae) and Adelomelon ancilla
(Subfamily Zidoninae) occur along the South Atlantic coast from 35°S, down to the Magallanes
Strait. These neogastropods are sympatric species in north Patagonian gulfs belonging from different
subfamilies, have different radula shape and position of salivary and accessory salivary glands, but
observations done in natural environment revealed that they have a similar feeding mechanism. In a
first step of capture, both species strongly engulfed the prey with their foot, creating a cavity which is
closed but not isolated from the environment. After around 10 hours, prey are narcotized by a white
liquid produced in the accessory salivary glands and introduced inside this cavity by the proboscides
(pH of salivary liquid is around 10). Prey narcotization leads to lower muscle speed reaction,
enabling the predator to feed on the prey fresh tissues by means of its radula. This organ is very sharp
in both species and tears the tissues of the living prey, so in the stomachs analyzed only a mucous
mass was found. Field observations suggest that narcotization is produced due to the constant release
of salivary liquid into the cavity generated by the foot, where the prey are immobilized.
The analysis of prey obtained by SCUBA diving indicated that O.magellanica and A. ancilla are top
predators in the benthic community, its diet consisting mainly in gastropods and bivalves. O.
magellanica mainly feeds on gastropods (54%) and bivalves (46%). Adelomelon ancilla mainly
consumes bivalves (90 % of the cases), follow by gastropods and in some isolated cases the sea
urchin Arbacia dufresnii (less than 2 % of the items).
In sandy bottoms, where aggregation of O. magellanica occurred but no other mollusks were found,
intraspecific cannibalism was registered in 4.7% of the cases while A. ancilla did not present
cannibalism.
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