The best replacement for hermit crab is snail.

The best alternatives to hermit crab are rated as following:
★★★★★  snail
★★  mantis shrimp
★★  fiddler crab
★★  betta fish
★  hermit crab
★  fancy hermit crab
  horse conch
  molted hermit crab

Your alternative for hermit crab is not listed? Suggest!
Speaking about hermit crab, one probably shouldn't forget about sea anemone.

Other search terms related to hermit crab and their ratings are:
★★★★★ sea anemone
You have in mind a companion for hermit crab and it is not yet here? Propose!



Google Trends

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hermit crab
snail
mantis shrimp