The sea animal is the prefix, and the pet is the suffix.
Sea Animal:
Crab: Thorn
Narwhal: Bright
Whale: Dark
Any fish: River
Jellyfish: Light
Shark: Tooth
Dolphin: Shine
Sea otter: Leaf
Sea lion: Loud
Other: Feather
Pet:
Dog: fur
Cat: pelt
Fish: scale
Bird: claw
Spider: foot
Reptile: song
Other: tail
Comment the name you get! ;)