Otherwise you are risking serious illness. From either pathogens of marine origin or later handling.
Crab: parasitic flukes (liver flukes and lung flukes), roundworms (e.g. Angiostrongylus cantonensis) and tapeworms (e.g. Diphyllobothrium spp.). Viruses: norovirus and Vibrio parahaemolyticus.
Lobsters: Vibrio parahaemolyticus, Vibrio vulnificus, Vibrio cholera.
Shrimp and Squid: many of the same.
Sources:
- https://seafoodbysykes.com/guide-to-eating-squid/
- https://www.cfs.gov.hk/english/multimedia/multimedia_pub/mul...
- https://www.vinmec.com/eng/article/is-it-safe-to-eat-raw-shr...
- https://www.nationthailand.com/in-focus/40012224