Pacific Rough Piddock Shell, Zirfaea pilsbryi
Pacific Rough Piddock Shell, Zirfaea pilsbryi. Shell collected off the beach of El Mezquital, Baja California Sur, December 2022. Size: 7.3 cm (2.9 inches) x 4.0 cm (1.6 inches) x 1.9 cm (0.7 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
Pacific Rough Piddock Shell, Zirfaea pilsbryi. Shell collected off the beach of El Mezquital, Baja California Sur, December 2022, Baja California Sur, May 2025. Size: 8.1 cm (3.2 inches) x 4.4 cm (1.7 inches) x 2.2 cm (0.9 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
Pacific Rough Piddock Shell, Zirfaea pilsbryi. Shell collected off the beach of El Mezquital, Baja California Sur, December 2022, Baja California Sur, May 2025. Size: 10 cm (3.9 inches) x 5.6 cm (2.2 inches) x 3.0 cm (1.2 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
Phylogeny: The Pacific Rough Piddock, Zirfaea pilsbryi H.N. Lowe, 1931, is a bivalve mollusk in the Pholadidae Family of Angel Wing Shells and Piddock Shells, and the Pholadinae subfamily. The Zirfaea Genus is one of six genera in this subfamily, and there are only two species in the Zirfaea Genus. This shell was named in honor of the American malacologist Henry Augustus Pilsbry of The Academy of Natural Sciences. They are also known as Pilsbry’s Piddock Shell and the Rough Piddock Shell.
Description: Pacific Rough Piddock Shells have an elongated quadrate outline and an inflated profile. The anterior end is beaked and the posterior is truncate (appearing chopped-off). These shells are robust and widely gaping at both ends. The exterior sculpting is divided into two zones by an oblique fold (sulcus). The posterior is marked with commarginal growth lines. These growth lines continue to the anterior end where they become imbricate (covered with sharp scales). These scales allow this species to bore into hard-packed clay. The interior is chalky, with obvious muscle attachment scars. Pacific Rough Piddock Shells are white, with a thin brown periostracum. They reach a maximum of 14.5 cm (5.7 inches) in length.
Habitat and Distribution: Pacific Rough Piddocks are generally found in burrows in clay, mud, shale, or sandstone. These burrows can reach 50 cm ( 19.7 inches) deep. Unlike most piddocks, this species can live outside its burrow for months at a time. They are found from the intertidal zone to a depth of 80 m (262 feet). Pacific Rough Piddock Shells are a boreal to subtropical Northern and Eastern Pacific species. They have a limited range in Mexican waters being found north of Magdalena Bay, Baja California Sur along the central and northwest coasts of the Baja Peninsula.
Ecology and Behavior: Pacific Rough Piddocks are suspension feeders that feed primarily on planktonic algae and suspended organic matter. They are prey for flatworms, gastropods, sea stars, sea otters, and shore birds, especially when they are young and have shallow burrows. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. Their engagement in any type of commensal, parasitic, or symbiotic relationship has not been formally documented, but their empty burrows are used as habitat by crabs, worms, and other bivalves. From a conservation perspective the Pacific Rough Piddock has not been formally evaluated. However, they are fairly common with a wide distribution and should be considered to be of Least Concern.
Synonyms: Zirfaea gabbii femii.