Marine Biology

Molluscs

Among lamellibranches, there are many efficient rock borers. At least in seven superfamilies of Bivalvia, such as Myacea, Adesmacea, Veneracea, Saxicavacea, Gastrochaenacea, Cardiacea and Mytilacea, the rock boring habit has been developed independently. In Mytilacea alone, boring is undoubtedly assisted by chemical means, and in others, boring is accomplished by mechanical means. Those which employ chemical means are solely restricted to calcareous rocks. The presence of others in calcareous rocks. The presence of others in calcareous rocks indicates only one of a range of substrates which they may use. The rock boring habit in the mentioned seven super families has been evolved either from a primitive infaunal habit or from an earlier active epifaunal habit . Thus, in some members of Myacea and all members of Adesmacea (Zirphaea crispate), the boring habit has been derived from a primitive infaunal habit, that is, from animals which burrowed into soft substrata by using foot. They have become specialized morphologically and have pre-adapted step-by-step for penetrating into stiffer and stiffer substrates until a true boring habit was evolved. In the other groups, Veneracea (Petricola pholadiformis), Saxicavacea (Hiatella arctica), Gastrochaenacea (Rocellaria cuneiformis) , Cardiacea (Tridacna crocea) and Mytilacea (Platyodon cancellatus, Botula falcate), the rock boring habit is reported.