This mod adds two different crustacean livestock to Stardew Valley as livestock you can adopt for your farm. The hermit crabs and giant isopods both go into the coop. They both bring back sea life that they hunt everyday. Hermit crabs bring back clams and snails, and giant isopods bring back sea cucumbers. The giant crab goes into the barn and it will bring back squids and octopuses.

The crustaceans bring some of their food, and they have their own section in the animal store.

It adds:
-Hermit Crabs
-Giant Isopods
-Giant Crabs

If you want to have crustaceans in game, you will need to add this:

    "Crustacean": {
      "Types": [
        "Hermit Crab",
        "Giant Isopod",
        "Giant Crab"
      ],
      "Buildings": [
        "Coop",
        "Big Coop",
        "Deluxe Coop"
      ],
      "AnimalShop": {
        "Name": "Crustacean",
        "Description": "Crustaceans prey on small ocean life",
        "Price": "6000",
        "Icon": "assets\\animal_shop_crab.png"
      }
    },

to the config.json in the Paritee's Better Farm Animal Variety folder. Obviously this means that this mod requires Paritee's Better Farm Animal Variety.
Which can be found here: https://www.nexusmods.com/stardewvalley/mods/3296

You also need to copy animal_shop_crab.png into Paritee's Better Farm Animal Variety (BFAV)'s asset folder.