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Giant clams were a large variety of the creatures of the same name, including oysters and scallops.[2][3]


A Serôsian locathah works to free his ally from a giant clam.

These were soft-bodied creatures that lived in the mantle cavity of protective shells. The abductor muscles of these creatures acted as a hinge for these shells and were quite powerful.[2][3] Lining the lips of their shell were numerous, hair-like cilia.[4] These were small tentacles about 2 feet (0.61 meters) in length, which they used to grasp and move prey. These were too weak to act in any defensive manner. And they used inhalant and exhalant siphons to move these shells across the ocean floor.[2][3]

The protective shell of a giant clam was vertically symmetrical[4] and on average were around 6 feet (1.8 meters) in diameter, though both smaller and larger specimens could be found. Their upper-shells were typically of a light brown hue, occasionally with white markings, while the lower-shell would be of a white hue. Near the edge of a shell were tiny blue eye-spots which performed the creature's senses. The inside of these shells were lined with mother of pearl. Some even held giant-sized pearls,[2][3] generally around the size of a grapefruit,[7] though these were not as lustrous as the pearls of mundane clams.[2][3]

Some species of giant clam had wavy-edged shells that were so sharp they could potentially sever a limb.[2] Those known as giant oysters had a more elongated and uneven shape, as well as a grayish hue.[4]


The eye-spots of these creatures could detect movement as well as distinguish between light and shadow. However, they could not estimate size.[2][3] In effect, they possessed a form of tremorsense.[1]

Near the front of a giant clam's mantle cavity were special organs that could detect and analyze chemical traces within the water around them.[2][3]


An aquatic humanoid struggles to free itself from the maw of a giant oyster.

Whenever a giant clam was threatened or something tried to reach within it, their protective shell would clamp down.[2][3] This was an instinctive defense mechanism, caused by their cilia being brushed against.[4] Many naturalists in the Realms insisted that these could not close fast enough to cause any serious injury.[8]


These creatures lived within small groups, though there existed persistent rumors that large beds of them could be found.[2]


Giant clams were primarily a filter feeding species, eating microscopic sea animals such as shrimp. They also lived on algae colonies that grew within their shell mantle.[2][3]


These creatures were typically found in shallow ocean waters, at depths of up to 200 feet (61 meters),[2] often in the vicinity of hydrothermal vents.[4][5] They were particularly known to be found within the Sea of Fallen Stars[9][10] within the oyster reef section of the Sea of Moving Ice,[8] within the Trackless Sea,[7] and within the Crowded Sea.[11]

In the Trackless Sea, many giant clams could be found throughout the stronghold Maelstrom.[7] In the Elemental Plane of Water, giant clams could be found around the coral reef compound known as Citadel of Ten Thousand Pearls.[12][13]


Communication with these creatures was not possible except on the most basic of empathic levels.[2]


Tritons were known to have domesticated giant clams and tended to beds of them.[2] Some giant clams acted as companions or servants of noble marids.[12]


The malenti colony of Kymal used giant clam shells as part of constructing their residences.[9] Likewise, some octopi were known to lair within giant clams.[4]

The shalarin of the Sea of Fallen Stars would carefully insert clothing constructed from sheeps' coral into the maws of giant clams, leaving them there for two months to be coated in their mucous. The shalarin then tempered that mucus with special shells, turning their clothing into pearl armor.[10]

Their tongues could be used as an ingredient for potions of giant size.[14] Their pearls could be used to create the soundbox of an 'Ud of the marids.[11]

The mother of pearl within their shells were worth around 50 to 500 gold pieces. And depending on their size and quality, a giant pearl could be worth around 500 to 1,000 gold pieces.[2][3] The rare black pearl of a giant clam was worth around 5,000 gold pieces.[7]

Rumors & Legends[]

  • Some rumors claimed that there existed intelligent, or even psionic, colonies of giant clams.[2]
  • Local legends around Marsember persistently claimed that obscure sea cults dwelled in the city that fed living sacrifices to giant clams.[15]


  • The field manuals of some navies in the Realms described methods of how one could escape from the clamped maw of a giant clam.[8]
  • The blue dragon Iymrith sometimes used her magic to transform her foes into giant clams.[16]



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  1. 1.0 1.1 1.2 Chris Lindsay (2018). Underworld Speculation (DDAL-XGE) (PDF). D&D Adventurers League: (Wizards of the Coast), p. 13.
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17  (1998). Monstrous Compendium Annual Volume Four. (TSR, Inc), p. 16. ISBN 0-7869-1212-X.
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 Chamberlain, Gray, Jones, Kopsinis, Maurus (December 1986). “The Dragon's Bestiary”. In Roger E. Moore ed. Dragon #116 (TSR, Inc.), p. 39.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Bryan K. Bernstein (February 1993). “Deep Beneath the Waves”. In Roger E. Moore ed. Dragon #190 (TSR, Inc.), p. 23.
  5. 5.0 5.1 Keith Francis Strohm (September 1997). Of Ships and the Sea. (TSR, Inc), p. 124. ISBN 0786907061.
  6. 6.0 6.1 Chamberlain, Gray, Jones, Kopsinis, Maurus (December 1986). “The Dragon's Bestiary”. In Roger E. Moore ed. Dragon #116 (TSR, Inc.), p. 39.
  7. 7.0 7.1 7.2 7.3 Christopher Perkins (September 6, 2016). Storm King's Thunder. Edited by Kim Mohan, Michele Carter. (Wizards of the Coast), p. 202. ISBN 978-0786966004.
  8. 8.0 8.1 8.2 Cryptic Studios (August 2016). Neverwinter: Storm King's Thunder. Perfect World Entertainment.
  9. 9.0 9.1 Steven E. Schend (1999). Sea of Fallen Stars. (TSR, Inc), pp. 51, 143. ISBN 0-7869-1393-2.
  10. 10.0 10.1 Steven E. Schend (1999). Sea of Fallen Stars. (TSR, Inc), p. 129. ISBN 0-7869-1393-2.
  11. 11.0 11.1 Jeff Grubb (February 1993). “Sounds of Wonder & Delight”. In Roger E. Moore ed. Dragon #190 (TSR, Inc.), pp. 84–88.
  12. 12.0 12.1 Wolfgang Baur (November 1993). Secrets of the Lamp. Genie Lore. (TSR, Inc.), pp. 31–32. ISBN 978-1560766476.
  13. Monte Cook (1996). The Planewalker's Handbook. Edited by Michele Carter. (TSR), p. 28. ISBN 978-0786904600.
  14. Christopher Perkins (September 6, 2016). Storm King's Thunder. Edited by Kim Mohan, Michele Carter. (Wizards of the Coast), p. 236. ISBN 978-0786966004.
  15. Ed Greenwood (July 1995). Volo's Guide to Cormyr. (Wizards of the Coast), p. 37. ISBN 0-7869-0151-9.
  16. Ed Greenwood (December 1997). “Wyrms of the North: Iymrith”. In Dave Gross ed. Dragon #242 (TSR, Inc.), p. 57.