Ditrupa arietina (O. F. Müller, 1776)

Synonyms:
Dentalium arietinum O.F. Müller, 1776
Serpula libra M. Sars, 1835
Ditrypa arietina McIntosh, 1923
Ditrupa arietina Fauvel, 1927

Distinguishing characteristics
Tusk-shaped tube.

Species description
10-12 pairs of radioli, connected at the base by a membrane. Operculum - membranous cup or funnel with a rather flat lens-shaped plate with concentric lines. Thorax with 6 chaetigers. Thoracic notopodial chaetae capillaries and slightly bent, winged chaetae. Neuropodia bear uncini with 16-22 teeth in a single row. Abdominal uncini like those on thorax. Capillary chaetae present on the most posterior 30-25 segments. Between thorax and abdomen two segments without chaetae. Pygidium with 2 round, small papillae. Tube - characteristic in being tusk-shaped, not adhered to substratum, made of two layers, the outer thick and vitreous, the inner thin and opaque.

Size
Over 20 mm long.

Color
Abdomen reddish, crown with reddish cross bands.

Habitat
Lives unattached to substrata (sand or mud). Sublittoral.

Mobility
Sedentary.

Feeding
Suspension feeder.

Life cycle

Distribution
Probably world-wide, English Channel, northern North Sea, Skagerrak, Kattegat and northern Öresund.