Margarita Worm Shell, Thylacodes margaritaceus

Margarita Worm Shell, Thylacodes margaritaceus. Shell collected off the beach in the greater Los Cabos area, Baja California Sur, May 2018. Size: 7.9 cm (3.1 inches) in length.

The Margarita Worm, Thylacodes margaritaceus (Chenu, 1844), is a gastropod mollusk that is a member of the Vermetidae Family of Worms. The shell is also known as the Mararita Tube Shell and in Mexico as caracol gusano and caracol de tubos. The shells usually have a flat profile and a flattened base. They grow in a fairly regular spiral with irregular patterns occurring when surrounding obstructions or overcrowding restrict their growth space. The shells are marked with strong lengthwise ridges. They are normally found as solitary animals. The shells are gray to brownish in color. The Margarita Worm Shells reach a maximum of 10 cm (3.9 inches) in length; they have apertures that are 1.0 cm (0.4 inches) to 1.3 cm (0.5 inches) in diameter.

Margarita Worms are found firmly attached to rocks and dead shells from the intertidal zone to depths up to 45 m (115 feet). They are found throughout the central and southern Sea of Cortez, and range south to Ecuador, including the Galapagos Islands. They have not been documented from along the West Coast of Baja.

Synonyms include Serpulorbis margaritaceus, Vermetus margaritaceus, and Vermetus margaritarum.