其腹面口区具二环围口纤毛列；背面具一列背刚毛。
There are two circumoral ciliary rows on the buccal region and a dorsal row of bristles.
为了减少磨损，提高活塞环的使用寿命，对整体无背压活塞环的设计进行了研究。
The design of integral non-backpressure piston rings was studied in order to reduce wear and to raise the piston ring life.
分别对开口有背压活塞环和整体无背压活塞环的工作原理和结构作了阐述。
The work principle and structures of backpressure piston rings and integral non-backpressure piston rings were expounded.
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