最原始的三胚层动物是（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='29829' and id < 2420918 and id<>'2420918' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='29829' and id > 2420918 and id<>'2420918' order by id asc limit 5