Mexican Chiton, Onchidella binneyi

Mexican Chiton, Onchidella binneyi. Chiton collected off a rock above the water line at Km 21, Cabo Real, Baja California Sur, April 2007. A unique collection made mid-morning as they were out in plain sight, moving fairly rapidly back to shelter, which was about 10 meters away. Size: 2.5 cm (1.0 inch). Identification courtesy of Dr. Richard Brusca, Tucson, Arizona.

Phylogeny: The Mexican Chiton, Onchidella binneyi (Stearns, 1893), is a gastropod mollusk that is a member of the Onchidiidae Family of False Chitons, a shell-less marine pulmonate gastropod mollusk. They are closely related to air-breathing land and freshwater snails and slugs than they are to most other sea snails and sea slugs.

Habitat and Distribution:  The Mexican Chitons are found along the western coast of the Pacific from the Bahía de los Ángeles in the Gulf of California to Ecuador. They are found within the intertidal zone just above the water line confined to the crack and crevices within large boulders on rocky coasts. They are not found in lower levels because they do not have strong enough grips to withstand the rising and falling tides and the harsh wave activity that occurs in the rocky intertidal zone. They are the most common Chiton found in Mexican waters.

Morphology:  The Mexican Chiton is a small air breathing sea slug that has a dome rounded profile.  They lack a shell and are oulmonate (having lungs versus gills). They possess a toxin, Onchidal, that provides them with a defense secretion. Onchidal has been demonstrated to inhibit Staph a indicative that it can inhibit Gram-positive bacteria and has been shown to be effective on lymphocytic leukemia cell growth in humans, various cancer treatments, and anti-inflammatory and cholesterol lowering effects. They have a long narrow foot. They are charcoal gray in color.  They reach a maximum of just over 2.5 cm (1.0 inches) in length.

Diet:  The Mexican Chiton activity is follows the rise and fall of the tides. During low tide episodes, when exposed to the air, they become very activity at night and emerge for feeding. They lack any adaptation that allows them to clamp tightly to rocks on the intertidal zones. Therefore, when wave surges happen on the shore, they are easily dislodged.

Reproduction: Reproduction of the Mexican Chiton is poorly studied and very little is known about their behavioral patterns.

Synomys:  Onchidella carpenteri, Onchidium carpenteri, and Oncidiella hildae.