Zebra Worm, Baseodiscus mexicanus

Zebra Worm, Baseodiscus mexicanus. Worm found within the tidal pools at Km 17, El Tule, Baja California Sur, December 2009. Length: 75 cm (2 feet 6 inches).

Phylogeny: The Zebra Worm, Baseodiscus mexicanus (Burger, 1895), is a member of the Valanciniidae Family of Ribbon Worms. The Baseodiscus Genus is one of eleven genera in the Valanciniidae Family, and there are forty-seven species in the Baseodiscus Genus.  They are also known as the Zebra Ribbon Worm and in Mexico as  Gusano Cebra. The genus name Baseodiscus comes from the Greek words meaning “base disk” or “pedestal disk”, but it is unknown what this name referrs to.

Morphology: Zebra Worms have firm bodies and broad rounded heads that can be withdrawn far into the body. They vary in color and may be brownish green, brownish violet, mahogany or maroon with numerous white rings encircling the body at regular intervals. The head is normally banded by a single white band. This coloration is very similar to that of the Zebra Moray, Gynomuraena zebra, and may be a form of mimicry. Due to their color, size, and shape the Zebra Worms are often confused by night divers with eels and sea snakes including the Red Banded Coral Snake, Calliophis intestinalis. When resting Zebra Worms reach a maximum of 76 cm (2 feet 6 inches) in length but they have the ability to expand dramatically to 4 m (12 feet) at night in their hunting mode. They are the largest, most abundant, nemertean in the tropical Eastern Pacific Ocean.

Habitat and Distribution:  Zebra Worms are found hidden under rocks and within the recesses of a reef during the day. They live in the intertidal zone, and to depths up to 24 m (80 feet), though some sources give the maximum depth as 100 m (328 feet). They are a subtropical to tropical Eastern Pacific species, however they have recently been reported in the Atlantic, the South Pacific and the Western Pacific including Japan, where they have apparently been introduced.  The Zebra Worm is found in all Mexican waters of the Pacific Ocean with the exception that they are absent from the extreme northern portions of the Sea of Cortez, and from the west coast of the Baja Peninsula, north of Todos Santos, Baja California Sur.

Diet: Zebra Worms prey on annelid worms and small crustaceans that they capture utilizing a long muscular proboscis armed with a barbed stylet.

Predators: Information specific to the predation of Zebra Worms has not been formally documented. Ribbon worms in general are preyed upon by shore birds, crabs, fish, and other ribbon worms. They secret a toxic slime which decreases the number of potential predators.

Reproduction: Information specific to reproduction of Zebra Worms has not been formally documented. Marine nemerteans of this order are generally gonochoristic (male or female for life) and reproduction is sexual. Fertilization occurs place externally. The eggs hatch into planktonic larval forms.

Ecosystem Interactions: Information related to any parasitic, commensal, or mutualistic relationships regarding Zebra Worms has not been formally documented.

Human Interactions: Zebra Worms have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Baseodiscus mexicanum, Eupolia mexicanus, Taeniosoma Mexicana, and Toeniosoma mexicana