American Sun Dial Shell, Architectonica nobilis
American Sun Dial Shell, Architectonica nobilis. Shell collected off the beach of Punta Chivato, Baja California Sur, May 2025. Size: 3.8 cm (1.5 inches) x 2.1 cm (0.8 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
American Sun Dial Shell, Architectonica nobilis. Shell collected off the beach of Punta Chivato, Baja California Sur, May 2025. Size: 4.4 cm (1.7 inches) x 2.2 cm (0.9 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
Phylogeny: The American Sun Dial Shell, Architectonica nobilis Roding, 1798, is a gastropod member of the Architechonicidae Family of Sun Dial Shells. The genus Architechtonica is one of twelve genera in this family, and there are eighteen species in this genus. They are also known as the Common Sundial.
Description: American Sun Dial Shells are solid, circular in outline, and made up of 6-7 whorls. They have a low conical profile and a flat bottom. The whorls are convex and each is sculpted with four beaded cords. The umbilicus is wide, deep, and bordered by a knobby keel. The area around this keel is sculpted with spiraling beaded cords. The aperture is oval and there is a small channel at the base of the columella. The exterior may be white, tan, or grayish brown, with brown spots along the spirals. American Sun Dial Shells reach a maximum diameter of around 4.4 cm (1.7 inches). These shells are very similar in appearance to the Karsten’s Sun Dial Shell, Architectonica karsteni. A. karsteni is less ornately sculpted, has more convex whorls, and different sculpting on the base. For a more complete discussion of the differences see Architectonica (Architectonica) karsteni (Rutsch, 1934): A Neogene and Recent Offshore Contemporary of A. {Architectonica) nobilis Roding, 1798 (Gastropoda: Mesogastropoda) by Thomas J. DeVries The Veliger 27(3):282-290 (January 2, 1985).
Habitat and Distribution: American Sun Dial Shells are found on a wide variety of substrates including rock, coral, sand, gravel, mud, and shell hash. They are found intertidally, and to depths of 183 m (600 feet). They are a widely distributed species found in subtropical and tropical waters of the Eastern and Western Atlantic and the Eastern Pacific. They are found along the entirety of Mexico’s east and west coasts, with the exception of the west coast of the Baja Peninsula, north of Magdalena Bay.
Ecology and Behavior: American Sun Dial Shells are predatory carnivores that primarily consumes zoanthids, coelenterates and other small invertebrates. Sources vary on the reproductive strategy for this species. Some sources say they are gonochoric and reproduce sexually through broadcast spawning. Others say they are sequential hermaphrodites that reproduce sexually with internal fertilization. Either way, this species has a long planktonic larval phase which accounts for its widespread distribution. There is no mention in the available literature of them engaging in any types of parasitic, commensal, or symbiotic relationships. From a conservation perspective they have not been formally evaluated, however they are widely distributed and fairly common.
Synonyms: Architectonica granulata, Architectonica sexlinearis, Architectonica valenciennesii, Architectonica wroblewskyi, Solarium granosum, Solarium granulatum, Solarium ordinarium, Solarium quadriceps, Solarium sexlineare, and Solarium verrucosum.