Drilling behaviour of Octopus mimus Gould

Abstract

The hole-drilling behaviour of the common octopus in North Chilean waters, Octopus mimus, on nine of its molluscan prey was studied in 70 specimens of 10–2000 g body weight in the laboratory. The occurrence of perforation was low, only 24.50% of the ingested prey were drilled. The bivalve Protothaca thaca (Molina) was the prey most frequently perforated, on 73.30% of occasions. The mean length of the P. thaca ingested increased significantly with octopus weight 2 (r 50.982, p,0.001) whether or not clams had previously been drilled. The form of the holes was usually a truncated cone with an oval section. The dimensions (length and width) of the external openings of the holes were significantly dependent on octopus weight and clam length ( p,0.001 in both cases). However, the dimensions of the internal openings of the holes were only dependent on octopus size. Location of the holes differed according to the prey species. Holes made in Mytilidae shells did not have any specific position, while the apex was the area selected for drilling the gastropod Concholepas concholepas (Brugie`re). The most specific location occurred when Protothaca thaca was perforated; 83% of the holes were located within or close to the myostracum of the anterior, mainly, and posterior adductor muscles of the clam. Within these small areas, there was a preference for the proximal edges.