Among 52 species of mollusca identified , 45 were gastropods, 7 were bivalves.是什么意思？

Among 52 species of mollusca identified , 45 were gastropods, 7 were bivalves.

调查期间采到的软体动物已鉴定52种,其中腹足类45种, 双壳类7种.

among

prep. （表示牵涉）经过，（表示位置）处在…中，（表示范围）在…之内，（表示所属）为…所特有；

例句
The system is failing most disastrously among less academic children.
这种制度对学习不太好的孩子效果最差。

species

n. 物种，种类，类型，[逻辑] 个体；

例句
Some animal and plant species cannot accommodate to the rapidly changing conditions...
某些种类的动植物不能适应迅速变化的环境。

of

prep. 关于，属于…的，由…制成；aux. 助动词 [非标准用语、方言] =have [主用于虚拟语气]；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

identified

v. 认出( identify的过去式和过去分词 )，支持，确认，辨认；

例句
He was identified only by his uniform and personal belongings.
他的身份只是通过制服和个人财物确定了下来。

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

bivalves

蚌类；

例句
The fauna in the Joli Fou consists of bivalves and arenaceous forams.
乔里富组内的化石主要是双壳类和砂壳有孔虫.