Your dungeon needs Cave Clams!

Celebrating Clam month! Dungeon clams you need them now. All settings.

Keep thinking of getting back to my undersea ruins dungeon design or compiling my maritime stuff.

Cave Clams, Mutated Animal, Neutral
Small HD 2 AC +5 d6 bite Mov 3 Swim 3 Climb 1
-on 20 to hit clam hangs on for d6 per round
Medium HD 5 AC +10 2d4 bite Mov 6 Swim 6 Climb 3
-on 19-20 to hit clam hangs on for 2d4 per round
Giant HD 12 AC +12 2d6 bite Mov 6 Swim 9 Climb 6
-on a 17-20 to hit clam hangs on for 2d6 per round

Cave clams are relatives of sea clams that live in caverns and cliffs and dungeons and sewers. They like to hide in cracks and crevices, strongly resemble stone or rock with a hard to see crack. Some are more colourful, some dig under floors or drop from above. Clams in hiding ambush on 1-4. Sometimes tiny ones cover floors looking like flagstones or rough boulder covered floors in a cave. The biggest one's mouths are like great doors that can swallow you up. Some especially under the lairs of evil alchemists. 1in4 have a pearl worth 100gp per HD. Larger ones are more mobile and several might accidentally cooperate. Some underland and underwater races cultivate them.

1in6 are Trench Clams with 4 "feet" +3 Move Burrow 3 in soil or mud, dig pits and trenches
1in6 are Dungeon Clams and they look like a secret door in the rock to lure you close
1in6 are Ram Clams, swap bite attack for knockback attack, affects HD equal to clams
1in8 are Fire Clams anyone touching or being snapped by one takes a d3 fire damage
1in8 are Ice Clams anyone touching or being snapped by one takes a d3 ice damage
1in10 are Invisible Clams that are concealed as the invisibility ability always on
1 in 10 are Jumping Jack Clams that can jump their HD in range once every three rounds
1in10 are Siege Clams shoot an 18 range indirect explosive glob grenade 2d4 1 wide circle
1in10 are Regenerating clams regrowing 1HP a round unless from acid or fire
1in12 are Displacer Clams, +2AC & first attack misses if not aware of displacement effect
1in12 are Blink Clams that teleport 3 range once per round after they bite
1in20 are Night Clams that generate 1 range radius of darkness per point of climb speed, they detect as evil and think dark clam thoughts constantly
1in20 are Chaos Clams have minor mutation per 2HD major mutation per 5HD, glow and scream and hide in dark muddy chaos bogs. Body parts stay lit for d4 days after death

d10 Cave Clam Adventures
1 The marsh fishermen started losing their dogs then children, now a legless survivor says it was damned giant clams!
2 Something crawls out of the well each night leaving a wet trail and making clacking sounds and anyone who goes to look is found decapitated
3 A child fell into a cave through a hole. An adult size entry by the old alchemist's ruined heap will let you get in to save the child. Locals all fear the dreaded clams and give up hope
4 A wet damp sinkhole by the sea was said to be where a pirate buried his treasure. A ship was sailed into a cave and sealed in. Adventurers may climb down the hole with ropes and help. Cave clams are in the lower parts of the hole before it opens into flooded cave of saltwater home of the great clam behemoth. Treasure is inside the clam and the sea entry was blown up by the pirate sealing his loot here
5 A small village popular with city visitors has had a clam outbreak as part of a curse. Fish folk hid an evil idol in a cave under the beach that is flooded and guarded by dread clams
6 A sea wizard made a dungeon only breathable for a few hours a day on the reef and marine cave clams infest it guarding an imprisoned sea nymph in a cave of pearls
7 A ship has been trapped by several enormous clams and the crew need help to fight the monsters and save the ship
8 A mermaid princess was eaten by a cave clam in a trench and her family seed someone to quickly rescue the body so she can be raised from the dead and still look pretty
9 A wizard has orcs and siege clams and has been attacking fortified buildings outside town
10 Migrating ram clams come ashore for ancient migration route, knock over everything in path and locals want help getting rid of them. Lots of poles slow or stop them best
11 A tribe of kobolds have been cultivating cams in the deep for aeons now have spares and they have been leaving pits with clams in the for idiots to fall in
12 Villagers years ago stored emergency supplies in cave and a recent check up had revealed cave clams living off rats had got in and grown too big to get past doors. These were a climbing variety who drop from the ceiling onto victims

Look out for those invisible fire trench ram clams that regenerate