V - The development of Haliotis Tuberculata , with special reference to organogenesis during torsion

Abstract

Investigation of the development of Haliotis tuberculata , Linnaeus, was undertaken as a natural sequel to an examination of the bionomics and anatomy of Haliotis (Crofts 1929, p. 159). It is an attempt to elucidate the organogenesis during the changing larval habits, in the hope of adding to the scanty ontogenetical evidence available towards solving the problems of gastropod evolution. Excellent accounts of the embryonic phase, including patiently worked out details of the cleavage and of gastrulation, have been published for Crepidula (Conklin 1897), Patella (Patten 1886; Wilson 1904; and Smith 1935), Trochus (Robert 1902), Physa (Wierzejski 1905), Dentalium (Wilson 1904). The only comprehensive accounts of gastropod larval development already published are of Paludina (Erlanger 1891; Tonniges 1896; Drummond 1902; Andersen 1924) and of Patella (Patten 1886; Smith I935). The accounts of Paludina elucidate the details of development of the coelom and its derivatives. The viviparous habit and consequent loss of free larval life in Paludina , however, make it a very unsuitable example of gastropod development. Evolutionary stages are more likely to be traced from the development of less specialized gastropods, an adequate selection of whose free-living larval stages can be obtained. The larval development of Patel, Acmaea, Trochus and Haliotis has been described, in varying completeness for the different genera. Patten’s work on Patella coerulea (1886) gives a description only of the beginning of organogenesis. After a lapse of fifty years a more detailed account of the development of P. vulgata has been given by Smith (1935). This work gives a new interpretation of the development of the mesoderm, of the muscles and of the nervous system. The dorsal retractor muscle of the larva, which Patten indicated for P. coerula , is shown in P. vulgata to be placed asymmetrically and torsion takes place “ under the action” of this muscle.