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Concussive Clam — Undersea Sourcebook

With an ear-piercing clap, the concussive clam snaps shut and rockets backward, out of reach. Check out this new D&D monster.

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The Undersea Sourcebook for Dungeons & Dragons 5e is a collection of player and GM options for running ocean-themed adventures. Subscribe for free weekly sea monsters and monthly encounters, right in your inbox.

Concussive Clam

These shell-armoured molluscs burrow in river and ocean beds and can also be found clinging to tidal rocks or the hulls of large ocean-going ships. When attacked, they use their powerful shell to create a deafening blast that shoots them backwards, away from danger.

Concussive clams are also known as clap clams, slam shells, or crack jacks. They are found in cold and warm oceans, at great depths as well as in shallow freshwater rivers.

Concussive clams live in colonies, but can occasionally be found alone. They are particularly tasty and those divers who make a living harvesting them are often hard of hearing.

Concussive Clam D&D Stats

In the next two weeks we’ve got two more monsters coming your way, including one iconic sea creature and the tentacled goblins of the sea, then a 1st-level encounter in the Crystal Caves featuring the new editions and the concussive clams. Here’s an initial design for the caves that didn’t make the cut:

Coral Caves 39x35 Map
Pretty, but we prefer hand-drawn maps, so this got scrapped early.

Have you got any ideas for using concussive clams in your game? Do you have a sea monster you’d like us to design or redesign? Let us know, in the comments below.

So, You’d Like to Read More, Would You?

Be sure to check out our roundup post for last month’s “No Dice” RPG Blog Carnival. We also recommend our State of the Phoenix post from the end of 2022.

Till the next monster arrives, have a good one. See you on the high seas!


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