Dolphins and seagulls belong to the class of animals, kelp belongs to the class of plants, while starfish and petrels belong to the class of other organisms.

1, dolphins are mammals with smooth bodies and flexible mobility, usually living in the water; gulls are birds with long wings and sharp beaks, usually flying near the coastline.

2, kelp is a large seaweed with flat blades and roots that usually grows on the bottom of shallow seas; starfish are echinoderms with pentagonal bodies and many tentacles that usually crawl on the seafloor.

3. The petrel, on the other hand, is a seabird with long wings and a sharp beak that usually flies over the sea.