Qiánshuǐ shí wǒmen kàndào le hǎojǐ zhǒng hǎikuòyú.
While diving we saw several different kinds of sea slugs.
Tips
memory
蛞蝓 by itself is the land slug. Add 海 ('sea') and you get the marine cousin. Both share the 虫 (worm/insect) radical, marking them as soft-bodied creatures.
