A loster has Transperannt blood which when comes in contact with air turns blue then why lobster is in phylum Arthropoda Mollusca even though it lives in water???

Dear student,
The blood of lobster is transparent but when it comes in contact with air it turns into blue due to the presence of copper which carries oxygen in the blood of lobsters. Lobster is an arthropod which lives in all kinds of oceans water.

Regards