What is the ruling on eating creatures that dwell in two worlds (living in sea and land), e.g crabs, is it haraam? Because some say there is a hadith that ban them?
Allah the Almighty commands:
“Say: I cannot find in what has been revealed to me anything forbidden for anyone who wants to eat unless it is carrion, outpoured blood and the flesh of swine, all of which is unclean; or that which is slaughtered in a name other than Allah as a deliberate sin. (…)” (6:145)
According to this verse, the foods which are forbidden to eat are carrion (animal carcass), blood, the flesh of swine and any animal over which the name of any other than Allah has been pronounced. We understand from the phrase “I cannot find in what has been revealed to me anything forbidden for anyone who wants to eat unless…” that all other animals are permitted to eat. Allah knows that there will be contradiction among Muslims about sea animals and He commands:
“Catch of the sea and the food from it have been made lawful for you and for the travelers as subsistence.” (Al-Ma’ida/ The Feast 5:96)
This verse also validates that all of the sea animals are permitted to eat wherever and however they are found. Whatever its names is, whoever catches it, either Muslim or non-Muslim, either it is dead or alive the same rule applies; those animals are lawful (halal).
The Messenger of Allah says:
“The water of the sea is clean, its carcass is permitted to eat.”
The amphibious creatures are no subject to a special ruling. They are lawful like every other creature besides the ones in [6:145] above.
 Abu Dawud, Taharat 41; Tirmidhi, Taharat 52; Nasai, Taharat 46; Ibn Majah, Taharat 38