Eurythoe complanata

About Eurythoe complanata

Eurythoe complanata is the name used in the Kauaʻi reef survey for an elongated fireworm in Amphinomidae. Its flattened, segmented body carries conspicuous white bristle bundles along both sides. Small, tree-like gills begin near the front and continue along much of the trunk. The rounded head has four eyes, three antennae and a pair of palps; the anterior eyes are larger than the posterior pair in the revised diagnosis. Behind the head, an elongated caruncle has a smooth median lobe and reaches approximately the third bristle-bearing segment.

The white brushes contain several kinds of chaetae, including harpoon-shaped notochaetae, spurred capillaries and smooth spines. Their microscopic structure helps distinguish Eurythoe complanata from Eurythoe laevisetis, a similar-looking species without the characteristic harpoon chaetae. These structures also explain why an attractive photograph alone cannot establish a precise identification. The bristles can irritate skin; the plate depicts the animal's anatomy rather than encouraging handling.

There is an additional genetic qualification. Research has separated morphologically very similar Atlantic and Pacific lineages within the Eurythoe complanata complex. The external morphospecies remains useful for interpreting historical records, but it does not resolve every lineage. The illustration is based on that published external diagnosis and does not identify the Kauaʻi worms genetically or establish their geographic origin.

Reproductive animals reported under this name can differ in colour: females have pink-red body regions, while males may be whitish as gametes develop. The paired reference forms show that documented contrast, not a photographed island breeding pair. A recent aquarium study retained its animals as Eurythoe cf. complanata after DNA comparison, reinforcing the need to keep lineage limits explicit. Sexual reproduction and fragmentation with regeneration are documented within the complex; regenerating pieces are not used as substitutes for complete animals in this plate.

The island entry comes from Kauaʻi rapid-assessment reef stations in Appendix B of Bishop Museum Technical Report 27, with 2002–2003 retained in the source evidence. It records the taxon as reported by that survey. General associations with coral rubble and sheltered spaces explain the reference habitat, without establishing present abundance, persistence, native status or a current distribution across Kauaʻi's reefs. The former plate remains available as a secondary reference.