97 



PHILIPPINE RUDITAPES, RUDITAPES PHILIPPINARUM 

 (ADAMS AND REEVE) 



(Veneridae) 



Veliconcha 



The anterior end of the shell is slightly longer than the posterior. The 

 shoulders are straight, slope steeply, and reach almost up to the middle of the 

 anterior and posterior margins. The umbones are broad and triangular-roundish 

 (see Figure 47). Concentric striation is distinct. The hinge system of the larva 

 at the veliconcha stage is represented by a row of denticles, generally num- 

 bering 12—14. The ligament is large and posterior. The length of the veliconcha 

 shell increases with the grov^h from 160 to 244 |im; its height is slightly less 

 than its length. The maximum length of the hinge line is 85 |im. 



Ecology 



In Vostok Bay (Peter the Great Bay), the larvae of this species are found 

 in July— August, and in Busse Lagoon (southern Sakhalin), in August-early 

 September, at a temperature of 15-23°C and 10-20°C respectively. 



The larvae of Ruditapes have been described by Yoshida (1935). 



MYA JAPONICA JAY 

 (Myidae) 



Veliconcha 



The shell is equivalve, with the posterior end somewhat shorter than the 

 anterior. The posterior margin is broad and slopes from the shoulders in a 

 straight line to the ventral margin. The anterior margin is narrow and round. 

 The shoulders are straight, broad, and slope downward. The shell length is 

 almost equal to its height. The umbo is initially indistinct and appears trian- 

 gular, its line margin with the line of the shoulders. Later, before the larva 

 settles, the umbo becomes roundish and distinct. The hinge system is weakly 

 differentiated. One provincular tooth is present on each valve. The ligament is 

 posterior. Weak concentric striation is distinguishable on the hollow valves of 

 the shell of the veliconcha. One of the main distinguishing characters of the 

 veliconcha of M. japonica is the presence of dark pigmentation on the soft 

 parts of the body in the region of the anterior and posterior muscles (retractors) 

 and along the velar margin (see Figure 45). Along the coasts of Primor'e, the 

 shell of the swimming larvae of M. japonica is 85—270 um long. Individual 

 specimens reach 300-320 |j.m. Larger larvae have been recorded along the 



