Asif, check these ones : 1) Joaquín Vierna, Andrés Martínez-Lage, Ana M. González-Tizón (2010). Analysis of ITS1 and ITS2 sequences in Ensis razor shells: suitability as molecular markers at the population and species levels, and evolution of these ribosomal DNA spacers // Genome, 53(1): 23-34; 2) Ana Insua, María J López-Piñón, Ruth Freire, Josefina Méndez (2003). Sequence analysis of the ribosomal DNA internal transcribed spacer region in some scallop species (Mollusca: Bivalvia: Pectinidae) // Genome, 46(4): 595-604