Feeding mechanism in volutids from north Patagonian shallow waters.

GREGORIO BIGATTI, C. J.M. SANCHEZ ANTELO Y PABLO E. PENCHASZADEH.

ANTWERP, BELGIUM

Congreso; 32- WORLD CONGRESS OF MALACOLOGY. ANTWERP, BELGIUM, 15-20 JULY 2007.; 2007

UNITAS MALACOLOGICA

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.