Plumularia setacea
Stems tall, pinnate, to 40 mm high, cauline internodes long, slender, widening distally to a distinct, transverse node; internode bearing one to three nematothecae, if all three present, equally spaced along internode, distalmost just below hydrocladial apophysis; if only one, this usually proximal on internode. Perisarc of stem thick proximally, thinning distally and along hydrocladia.
Hydrocladia alternate, inserted on an upwardly tilted distal apophysis; apophysis with one or two strong transverse nodes followed by a slightly oblique distal node; first hydrocladial internode hydrothecate, internodes thereafter alternately athecate and thecate; two or three hydrothecate internodes on hydrocladium, internodes long and slender, nodes slightly oblique, distinct; thecate internode widening from proximal node to base of hydrotheca.
Hydrotheca on distal third of internode, abcauline wall confluent with internode, adcauline wall almost entirely adnate, convexly curved, free part short, straight, margin circular, tilted distally at an angle of c. 105° to hydrocladial axis; athecate internode with a small mesial nematotheca at proximal third to centrally placed, inclined towards hydrocladium, basal chamber short, robust, cup a little foreshortened on adcauline side;
mesial nematotheca proximal on hydrothecate internode, same as athecate mesial; lateral nematotheca small, freely movable, facing outwards, basal chamber inserted without pedicel in internode beneath hydrotheca, cup small, circular; cauline nematothecae same as mesials. Perisarc of hydrocladia and hydrotheca thin; hydranth with 12- 14 tentacles.
Colour: White.
Near-cosmopolitan in subtropical and temperate seas.
Subtidal, epizoic on polychaete tubes and other invertebrate substrates.