Large-coiled Whelk Shell, Solenosteira macrospira

Large-coiled Whelk Shell, Solenosteira macrospira. Shell collected off the beach of Bahía Concepción, Baja California Sur, October 2019. Size: 5.6 cm (2.2 inches) x 3.7 cm (1.4 inches).  Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

The Large-coiled Whelk, Solenosteira macrospira (Berry, 1957), is a gastropod mollusk that is a member of the Pisaniidae Family of False Triton. The shells are stout with a with a large body whorl and a moderate spire and is decorated with numerous, fine, spiral, ridges and many, heavy, length-wise, ribs. They have a large aperture, which has an outer lip marked with fine teeth, that descends to a wide siphon canal. The exterior of the shell is white in color, with tan to brown blotching; the interior is white. Large-coiled Whelk Shells reach a maximum of 6.6 cm (2.6 inches) in length and 4.4 cm (1.7 inches) in height.

Large-coiled Whelks are found on and within sand substrate from the intertidal zone to depths up to 5 m (15 feet). They reside throughout the Sea of Cortez and have not been documented from the west coast of Baja or mainland Mexico. They are not known for their traditional family values. The females mate with as many as twelve different males. She then lays her eggs on a male, who will carry the eggs for about one month. On average, only one-quarter of the eggs will be his offspring’s – the rest belong to other males. As the eggs develop, they become cannibals and feed on their siblings with the host male unable to stop this behavior.

A synonym is Hanetia macrospira. Historically this species has been placed in the Buccinidae Family and has been recently reclassified into the Pisaniidae Family.