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；

species

n. 物种，种类，类型，[逻辑] 个体；

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]；

identified

v. 认出( identify的过去式和过去分词 )，支持，确认，辨认；

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；

bivalves

蚌类；