. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 30 ANNALS OF THE SOUTH AFRICAN MUSEUM madagascariensis were bored. In the case of the former an equal number of right and left valves were bored, as would be expected in view of the fact that it burrows in a vertical position. Analysis of predation on T. madagascariensis reveals a very different pattern. Successfully bored valves fell into two size- classes (Fig. 2H). The first group comprised juveniles with a size range 20-22 mm, and the second group adults with a size range 46-64 mm. Only right val
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 30 ANNALS OF THE SOUTH AFRICAN MUSEUM madagascariensis were bored. In the case of the former an equal number of right and left valves were bored, as would be expected in view of the fact that it burrows in a vertical position. Analysis of predation on T. madagascariensis reveals a very different pattern. Successfully bored valves fell into two size- classes (Fig. 2H). The first group comprised juveniles with a size range 20-22 mm, and the second group adults with a size range 46-64 mm. Only right valves of adults were bored, which is to be expected because this species lives buried in sediment in a horizontal position and with right valve uppermost. Craig (1967) found that the right valve of Tellina radiata was also preferentially bored. The second group of T. madagascariensis comprised juveniles in which left valves were preferentially bored, although a few right valves were also bored. The preferential boring of juvenile left valves could also be the result of the burrowing characteristics. Tellina is a rapid burrower (Stanley 1970). Depth of burrowing would be controlled by length of the siphons, and for this reason the juveniles would presumably live at shallower depths than the adults and would possibly burrow more slowly. Subsequent current scour would possibly reach only the juveniles and flip them over to leave them left valve uppermost. This also suggests that, besides predation, the juvenile bivalves would be more susceptible to environmental changes since they live closer to the surface. Most of the bored bivalve shells have only one hole, which is not surprising since only one puncture is necessary to kill the animal. In a few cases two holes per shell were encountered. As far as Tellina madagascariensis is concerned the borings occur most frequently in the antero-dorsal half of the shell (Fig. 3). It was also observed that all bored specimens of T. madagascari
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
