Genus Hydroides Gunnerus, 1768

Type-species: Hydroides norvegicus Gunnerus, 1768

Number of species: 95

Diagnosis. Tube white, circular or trapezoidal in cross-section. Distinct keels absent. Operculum with a soft basal funnel of fused radii and a distal crown of chitinized verticil spines arising from center of funnel radii. Peduncle cylindrical, smooth, without wings. Pseudoperculum present. Radioles arranged in semi-circles; stylodes and branchial eyes absent. Thorax with seven chaetigers. Collar trilobed, tonguelets absent. Thoracic membranes long, forming ventral apron. Collar chaetae bayonet and limbate. Subsequent chaetae of two sizes, limbate and capillaries. Apomatus chaetae absent. Uncini along entire thorax saw-shaped, anterior fang pointed. Abdominal notochaetae uncini, neurochaetae flat trumpet-shaped.