Monster Monday: Giant Sea Slug, Stinging Mollusk of the Reefs

Today's Monster Monday is the giant sea slug or giant nudibranch. These colorful, poisonous, acid-spitting creatures lurk in reefs or the open sea, feeding on coral and giant jellyfish, occasionally swarming shipwrecks or attacking castaways.

Clockwise from top left: Nembrotha aurea, Berghia coerulescens, Glaucus atlanticus (sea swallow or blue dragon), and Hexabranchus sanguineus (Spanish dancer). Via Wikimedia.

Sea slugs are carnivorous shell-less mollusks, far more varied and colorful than the garden slugs with which we are all familiar. Some crawl along the seafloor, others - like Glaucus atlanticus - cling to the surface tension of the water, and still others - like the Spanish dancer - can ripple and undulate through the water. In nature, sea slugs become poisonous by absorbing the stinging cells of jellyfish and hydrozoans that they eat, thus turning their prey's defenses into their own.

Giant sea slugs, as statted up below, combine elements from many different real species of sea slug, except instead of being tiny they are ten feet long and capable of feeding on giant jellyfish and even humans.

The following text in gold is available as Open Game Content under the OGL. Open Game Content is ©2018 Jonah Bomgaars.

A brightly colored sea slug ripples through the water like a fluttering ribbon

Sea Slug, Giant   CR 3

XP 800

N Large vermin (aquatic)

Init +2; Senses darkvision 60 ft.; Perception +0

DEFENSE

AC 16, touch 11, flat-footed 14 (+2 Dex, +5 natural, -1 size)

hp 30 (4d8+12)

Fort +7, Ref +3, Will +1

DR 5/slashing or piercing; Immune acid, poison, mind-affecting effects

Defensive Abilities amorphous

OFFENSE

Speed 20 ft., swim 20 ft.

Melee bite +4 (1d8+2 plus 1d6 acid), slam +4 (1d6+2 plus poison)

Space 10 ft.; Reach 10 ft.

STATISTICS

Str 14, Dex 15, Con 17, Int --, Wis 10, Cha 1

Base Atk +3; CMB +6; CMD 18 (can’t be tripped)

SQ compression

SPECIAL ABILITIES

Poison (Ex)

Slam or Stinging Touch – injury; save Fort DC 15; frequency 1/round for 6 rounds; effect 1d4 Dex; cure 2 consecutive saves.

Stinging Touch (Ex)

Creatures striking the giant sea slug with a natural attack or unarmed strike are subject to the slug’s poison attack.

ECOLOGY

Environment temperate or warm oceans

Organization solitary

Treasure none

The giant sea slug is a massive, ten-foot-long gastropod that crawls along the ocean floor or flutters through the water by rippling its ribbon-like body. These creatures are often very colorful to ward off potential predators. Sea slugs make their bodies poisonous by absorbing toxins or stinging cells from the sponges and jellyfish they eat.

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Plot Hooks and Encounter Ideas

• Rumor has it that the merfolk's pearls are stored in a cave guarded by giant stinging sea slugs and other undersea terrors.
• Giant sea slugs ripple and slide through the gaps in the reef that your ship has just run aground on.
• Just beyond the garden of anemones, the bare streets of the sunken city are patrolled by a massive nudibranch.

-your opisthobranch d20 despot