Petromyzontidae lack centra and have a persistent notochord .
七鳃鳗科缺乏中心椎盘而且有一个连续的脊索。
The implied claim that mine was the centra role was bound to be an affront to any president .
这种意味着自称我起了中心作用的话，肯定要得罪任何一位总统。
Duke university 's fuqua school of business has taken a similar approach , using programmes such as itunes and centra as publishing mechanisms for the webcasting of lectures which can be watched live or downloaded at a later time .
