. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. THE OF LATJIRXULA TRUXCATA 525. FIGURE 13. Latcnnilu tntncafa, a horizontal section through the shell to demonstrate the method of movement of the shell valves. Abbreviations are: AA, Anterior adductor muscle; CL, Clavicle; CS, Crack in shell; FU, Fulcrum; PA, Posterior adductor muscle. The microstructure of the shell of the Pandoracea is most similar to that of the Poromyacea (Taylor et al., 1972). The thinness of the shell in L. trnncata in par- ticular and in the Pandoracea in general (Taylor, et al., 1972) possi
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. THE OF LATJIRXULA TRUXCATA 525. FIGURE 13. Latcnnilu tntncafa, a horizontal section through the shell to demonstrate the method of movement of the shell valves. Abbreviations are: AA, Anterior adductor muscle; CL, Clavicle; CS, Crack in shell; FU, Fulcrum; PA, Posterior adductor muscle. The microstructure of the shell of the Pandoracea is most similar to that of the Poromyacea (Taylor et al., 1972). The thinness of the shell in L. trnncata in par- ticular and in the Pandoracea in general (Taylor, et al., 1972) possibly represents another step in the trend of this group towards a sedentary mode of life. The thinness of the shell in L. trim-cat a has necessitated the development of a clavicle or strengthening strut for each shell valve. Such a system is not designed to pro- tect the animal from external damage, but from the internal compression forces created by the adductor muscles. A further modification has been the development of a lithodesma which effectively fixes the ligament, thereby preventing the shell valves from opening under the pressure exerted principally by the primary ligament and by the secondary ligament of fused periostracum. The secondary ligament is also found in other genera of the Pandoracea, , Pandora and Cochlodcsina (Allen, 1954; 1958) and Entodcsma and Mytilimeria (Yonge, 1952) although only in the latter two genera is there a lithodesma. A lithodesma occurs in M\dora, Mvochatna and Chamostrea (Thiele, 1935), and in Thracia (Tebble. 1966). The trend in the Pandoracea towards the relative immobilization of the ligament by means of a lithodesma has resulted in L. tnmcata in the adductor muscles being relatively small and ineffectual. This is especially true of the posterior adductor. The pedal retractors of the adult are similarly very small. It would thus seem that shell movements in Later mil a (Fig. 13) are small and are brought about by the contraction of (
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
