Diet composition and feeding habits of Mactra veneriformis
DNA extraction.  The stomach contents were homogenized after being washed with phosphate buffer (pH 7.2-7.6). The whole DNA was extracted according to the instructions using the Marine DNA Extraction Kit (Tiangen, Beijing, China). The acquired total DNA was measured using a UV spectrophotometer, identified by electrophoresis using 0.8% agarose gel, and the qualified DNA was kept at -20C. High-Throughput Sequencing.  The PCR reaction was conducted in a 20 L system and sample DNA was amplified by PCR using the 23S rDNA primers p23SrV_f1 (5-GGA CAG AAA GAC CCT ATG AA-3) and p23SrV_r1 (5-TCA GCC TGT TAT CCC TAG AG-3)65. 10 ng of DNA template, 0.5 L of Q5 high-fidelity Taq enzyme (NEB, Beijing, China), 1 L of each of the positive and negative primers (5 mol/L), 4 L of 5 buffer, and 2 L of dNTPs (2.5 mmol/L) were used. With a reaction cycle of 29, the PCR process was as follows: pre-denaturation at 95 C for 7 min, denaturation at 95 C for 45 s, annealing at 55 C for 30 s, extension at 72 C for 45 s, and final extension at 72 C for 10 min. Then the PCR products were identified using 2% agarose gel electrophoresis, and purified by, and purified by AxyPrep DNA Gel Extraction Kit (Axygen, Silicon Valley, USA) before being submitted to bipartite sequencing on the Illumina Miseq sequencing platform (Illumina, San Diego, USA).