arrow crab or reef lobster?

[cherubfish pair]

for a scavenger?

 

[Betta132]

Neither.
Arrow crab will eat small fish, reef lobster will attack fish.
Just stick with hermit crabs.
Like you were told in the first thread you posted asking this.

 

[650-IS350]

hermits.

 

[snorvich]

Neither.
Arrow crab will eat small fish, reef lobster will attack fish.
Just stick with hermit crabs.
Like you were told in the first thread you posted asking this.

This. Most shrimp are excellent scavengers.

 

[650-IS350]

but some can also turn on your corals like peppermints. or steal food from your lps like cleaner shrimps and Peps can.

 

[Calappidae]

Personally,
Serpent starfish, nothing beats them. Safe, effective, cool to watch.

Reef lobsters are more something best left in a species tank.