55 



quired to examine the structure of the valve hinge in each larva. It is necessary 

 to separate the valves and mount them for microscopic examination at high 

 magnification. The method proposed by many researchers (Turner and Boyle, 

 1974; Schweinitz and Lutz, 1976; Lutz and Hidu, 1979; Le Pennec, 1980), 

 based on a detailed examination and comparison of shell structures and hinge 

 systems using a scanning electron microscope, ensures accuracy of identifica- 

 tion but is not practicable for working v^ith a large number of larvae. Iden- 

 tification predominantly based on size parameters of larvae also does not 

 guarantee total accuracy since the larva of each species, even at the same 

 stage, may change shape during growth; this hardly ensures constancy of 

 relative size parameters. Hence, in preparing a key to the identification of 

 larvae to family, it is expedient to use shape of shell as well as some more 

 apparent individual characters, such as presence of dark pigmentation in mem- 

 bers of the family Myidae or ocular spots in Mytilidae as the main taxonomic 

 characters; these are retained in fixed specimens and are readily visible under 

 a binocular microscope. Size parameters of larvae and structure of hinge are 

 better used as second-order characters. 



Key to Families for Larvae of Veliconcha Stage 



The structure of the veliconcha shell according to families is presented in 

 Figure 36 (larvae arranged with anterior and left and posterior and right). 

 Orientation of larvae in photos random. 



1 ( 4). Shell inequivalve. 



2 ( 3). Valves differ considerably in shape and size. Left valve large, con- 



vex, with high umbo raised above right valve. Right valve small, 



flat, with low umbo. Anterior and slopes sharply. Pigmented eyes 



, absent Ostreidae, Figure 37. 



3 ( 2). Valves differ slightly in shape and size. Left valve slightly more 



convex than right. Anterior and highly raised. Pigmented eyes present 

 Pectinidae, Figures 38, 55, 56. 



4(1). Shell equivalve. 



5(10). Shell round or nearly round. 



6 ( 7). Shell flat, slightly colored, large. Valves thin, brittle. Umbones in- 



distinct or very small. Striation barely perceptible 



Kelliidae, Figure 39. 



7 ( 6). Shell convex, intensely colored, moderate in size. Valves thick strong 



Umbones high, round. Striation well defined. 



8 ( 9). Height of shell slightly more than or equal to length. Hinge system 



with three large rectangular teeth on right valve and two on left. . 

 Teredinidae, Figures 40, 63, 64. 



