Placostegus tridentatus (Fabricius, 1779)

Synonyms:
Serpula tridentata J.C. Fabricius,1779
Serpula crystallina Kupffer, 1873
Placostegus tridentatus McIntosh, 1923

Distinguishing characteristics
Tube triangular in cross-section with 3 teeth.

Species description
Crown with 9-15 pairs of long radioli, without a basal membrane. Operculum with a brownish concave distal plate bearing a knob-like projection within the funnel-shaped ampulla. Thorax with 6 chaetigers, all with notopodial capillary chaetae and neuropodial uncini. First chaetiger without collar chaetae. Thoracic notopodial chaetae capillaries with broad wings, uncini quadrangular, with numerous small teeth. Abdominal chaetae capillary and chisel-formed. Uncini like those of the thorax. Tube - translucent; triangular in cross-section, with a median keel which extends over the aperture as a 'tooth', and flanges against the substratum which end as two additional teeth if the anterior becomes erect.

Size
Up to 30 mm long.

Color
Crown dark red, with 2 brown cross-bands.

Habitat
On stones and shell.

Mobility
Sedentary.

Feeding
Suspension feeder.

Life cycle

Distribution
Arctic, northern and middle Atlantic up to Mediterranean, northern North Sea, Skagerrak, Kattegat, the Belts.