Zhè / zhǒng / hǎi / mián / de / gǔ / zhēn / zhǐ / néng / zài / xiǎn / wēi / jìng / xià / guān / chá / dào

这种海绵的骨针只能在显微镜下观察到。

The spicules of this type of sponge can only be observed under a microscope.