Georgette Douwma / Mantel of Spiny oyster (Spondylus varius). Indonesia. Indo-West Pacific.

Georgette Douwma / Kaleidoscopic image of Thorny oyster (Spondylus varians) pattern on mantle. Ceby, Malapascua Island, Philippines.

Georgette Douwma / Thorny oyster (Spondylus varians), pattern of mantle. North Sulawesi, Indonesia.

Linda Pitkin / Variable thorny oyster (Spondylus varius) Rinca, Komodo National Park, Indonesia.

Pascal Kobeh / Necklace starfish (Fromia monilis) on variable thorny oyster (Spondylus varius), Maldives, Indian Ocean. This starfish is a predator of oysters.

Pascal Kobeh / Close-up of a Variable thorny oyster (Spondylus varius / varians) on a coral reef, Maldives. Indian Ocean.

Ingo Arndt / Regal Thorny Oyster (Spondylus regius), Meeresmuseum Ozeania, Riedenburg, Germany

Ingo Arndt / Thorny Oyster (Spondylus echinatus) from Thailand, Meeresmuseum Ozeania, Riedenburg, Germany

Ingo Arndt / Regal Thorny Oyster (Spondylus regius), Meeresmuseum Ozeania, Riedenburg, Germany

Birgitte Wilms / Oyster (Spondylus varians) with closed mantle, Solomon Islands

Birgitte Wilms / Oyster (Spondylus varians) with partially open mantle, Solomon Islands

Chris Newbert / Oyster (Spondylus varians) mantle, 60 feet deep, Solomon Islands