Macrophthalmus pacificus is a species of sentinel crab found widely across the Indo-West Pacific Ocean, including India, Japan, Malaysia, New Guinea, Solomon Islands, and northern Australia.

[1] M. pacificus lives in mud in tidal zones of river mouths' adjacent mangrove forests in low tide areas.

The claws of adult males are sky blue.

[3] It is often found feeding in shallow still water, and in soft mud.

Like other Macrophthalmus species, the claws of the male are larger than those of the female.