What's this on the trail to the beach?
They just keep on coming. ... Evil crabs and shellfish are invading the Massachusetts coast.
The Chinese Mitten crabs, which arrive as stowaways in ballast water, can do a lot of damage.
The Rapa Whelks meanwhile are eating up their competitors. Apparently these Asian origin shellfish grow too large for the local turtles to consume -- and then chow down on the local clams, oysters and mussels.
As for the third alien, I couldn't find much except this description this description from a Texas source.
The town boards that encourage the shell fish industry and the Martha's Vineyard Conservation Society are offering a reward to people who apprehend one of the invaders. Since I've already got a copy of the trail guide (it's great), I think I might pass any I found to some child who would receive a more desirable prize.