双壳贝

Origin, developmental changes and homologies of the stage morphostructures were considered according to their location in three morphogenetic fields. The first, or central, field forms at the prodissoconch I stage. It can be inherited by prodissoconch II and nepioconch stages in one taxa, or PD-II, N and dissoconch stages in others. The second, or postero-dorsal, field appears at the N stage, and the third field, or antero-dorsal, at the D stage.

主要对3个形态发生区域的阶段形态结构的起源、发育变化和同源性做了研究，其一，即中央区域，开始形成于前双壳I期，在某个分类单元它可以在前双壳II期和幼贝期形成，而在其它分类单元则在前双壳II期、幼贝期和双壳期形成；第二区域，即背部后区，在幼贝期出现；第三区域，即背部前区，出现于双壳期。

Origin, developmental changes and homologies of the stage morphostructures were considered according to their location in three morphogenetic fields. The first, or central, field forms at the prodissoconch Ⅰ stage. It can be inherited by prodissoconch Ⅱ and nepioconch stages in one taxa, or PD-Ⅱ, N and dissoconch stages in others.

其一，即中央区域，开始形成于前双壳Ⅰ期，在某个分类单元它可以在前双壳Ⅱ期和幼贝期形成，而在其它分类单元则在前双壳Ⅱ期、幼贝期和双壳期形成；第二区域，即背部后区，在幼贝期出现；第三区域，即背部前区，出现于双壳期。

Any of several freshwater bivalve mollusks of the genera Anodonta and Unio, found in the central United States, that burrow in the sand or mud of lakes and streams.

淡水蚌发现于美国中部的无齿贝属和珠蚌属几种淡水双壳软体动物的一种，在湖和河中的沙中或泥中挖洞

When the Thompson quadruplets espied him one day,they called him a bivalve and ran quickly away.

有一天，汤普森家的四胞胎看见他，&双壳贝！&

When the Thompson quadruplets espied him one day, they called him a bivalve and ran quickly away.

有一天，汤普森家的四胞胎看见他，&双壳贝！&喊完后一溜烟的跑走了。

They are important members in marine sessile communities because their leathery tunic provides habitats for other organisms, such as bivalves, polychaetes, echinoderms and other ascidians.

它们的革质外鞘可以提供其他动物附生，例如：双壳贝、多毛虫、以及其他种海鞘等都是常见附生动物。

Chrysanthemum of 10 thousand birthday is lax to edaphic requirement, with the arenaceous qualitative loam with fecund, good drainage had better.

万寿菊对土壤要求不严，以肥沃。排水良好的砂质壤土为好。

He unstepped the mast and furled the sail and tied it.

他拔下桅杆，把帆卷起，系住。