Amphionomidae Family of Bristle Worms

Gulf Fireworm, Eurythoe complanata.  A representative of the Amphionomidae Family of Bristle Worms.

Phylogeny:  The Bristle Worms are members of the Amphionomidae Family with one hundred thirty-eight species of which eleven are found along the Pacific Coast of Mexico. They belong to the Phylum Annelida. They are in the Class Polychaeta (which comes from the Greek words meaning “many bristles”) and the Order Amphinomida. They are similar to earthworms and in Mexico are known as Gusanos de Cerdas.

Distribution:  Bristle Worms are found globally, primarily throughout the tropics and subtropical regions, but some species are found in temperate and even boreal waters. Most are found in shallow waters, but some are found at depths exceeding 12,000 feet. Bristle worms are found in a variety of habitats including coral reefs, kelp plants, mud, rock reefs, sea glass beds, sands beds and on floating logs and flotsam.

Morphology:  Bristle Worms have bodies that are composed of ringed segments and each of their body segments has a pair of bundled bristles (chaetae) and a pair of foot-like projections. In some species, these “feet” are paddle-like, to assist with swimming, burrowing, and creating a feeding stream. Other than the head and terminal segment, all the segments are identical. Bristle Worms are flattened and oblong or ovate-oblong in shape. The cephalic lobe is rounded or compressed. They have two pairs of eyes, with either both pairs mounted dorsally, or one pair dorsal and one pair ventral. The bristles of most polychaete are made of chitin. The bristles of Amphinomidae Bristle worms however are calcareous. The bristles are hollow and harpoon-like. Some species are known as Fire Worms because when handled they cause a long lasting very painful burning sensation. The bristles of Fire Worms are filled with complanine, an organic molecule that is an ammonium salt. If the spines puncture skin or mucous membrane, they break off and release the complanine, which causes intense burning pain and inflammation. First aid for Fire Worm “burns” include applying vinegar or isopropyl alcohol and removing the spines with tweezers. They reach up to 35 cm (13.8 inches) in length. Many tropical species of Bristle Worms are brightly colored.

Ecosystem Roles:  Amphionomidae consume coral polyps, crustaceans, detritus, mollusks, and sponges. Their bristles are highly effect to ovoid predation. Mollusks, especially cone shells (Conus sp.), are their primary predators.

Reproduction:  Bristle Worms are capable of both a sexual and sexual reproduction. Asexual reproduction occurs when a series of segment breaks away and regenerates a head, terminal segment, or both. During sexual reproduction, the male and females swim to the water’s surface; the female displays bioluminescence, either to attract a mate or to repel predators.