Hydroides dirampha

About Hydroides dirampha

Hydroides dirampha is a marine bristleworm that secretes a white calcareous tube on a hard surface. The living animal is slender and segmented, with a paired crown of finely feathered radioles at its front. A stalk beside that crown carries an operculum, the plug used when the worm withdraws into its tube. Identifying this species depends on the shape of that plug and microscopic chaetae, rather than on the mere presence of a white tube or feeding fan.

Sun, ten Hove and Qiu’s Hong Kong material had seven thoracic chaetigers and a much longer abdomen, with total lengths of 12–32 mm. Their radiolar lobes contained fourteen to eighteen radioles per side. The operculum has two tiers: a lower funnel with pointed radial tips and an upper circle of straight yellowish spines. Each upper spine ends in a flattened T-shaped tip and has a basal internal spinule. Lateral and external spinules and a central tooth are absent. A small club-shaped pseudoperculum accompanies the principal plug in adults; the 2002 Atlantic revision did not observe it in two juveniles. Counts vary between studies and are not fixed measurements for Kauaʻi animals.

The radiolar crown is the suspension-feeding apparatus of a serpulid tubeworm. The tube protects the body and anchors it to its substrate. Published records include natural hard surfaces and harbor fouling on pilings, hulls, ropes and settlement plates. The species can be transported with fouling communities, but its presence alone does not show that a particular local specimen arrived on a ship. Bastida-Zavala and colleagues treated it as cryptogenic in their 2017 review because its original geographic range remains uncertain. That uncertainty supports retaining the Atlas’s unresolved-origin status.

Kauaʻi inclusion rests on the 2002 survey or historical compilation retained in Bishop Museum Technical Report 29a, Appendix A, printed page 90. It does not establish a 2026 population, island-wide distribution or a measured ecological impact. The plate reconstructs published adult and juvenile reference anatomy. Their tubes are opened for anatomical display so the intact bodies and posterior ends can be seen; this is not normal exposed feeding posture or a photograph of the local voucher. No unsupported male–female colour contrast is assigned.