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Von Nordheim, 1989

Description:
Septum 2 and 3 incompletely developed. Tentacles comparatively long (300-420 µm). No eyes in adults; no so-called statocysts. Nuchal organs oval. Each segment with one pair of small adhesive organs, comprising one or two glands in the anteriormost segments and three to six from segments 7, 8 or 9 posteriorly. Bacillary glands sigmoid, few on dorsal side and 8-12 on each side of ventral ciliary band. Females with cocoon glands laterally from segment 7, 8 or 9 backwards, and dorsally from segment 12. Dorsally one complete ciliary ring at level of pharynx bulb; small rows of cilia directly behind base of each tentacle. Small ciliary tufts and numerous (mostly short) sensory cilia scattered over body, especially on the head and on the lateral sides of the trunk; sensory cilia of various lengths, especially dense on posterior end. Two elongate adhesive pygidial lobes, terminally enlarged and with rounded margin. Transparent salivary glands through segments 4 or 5.
Two pairs of spermioducts in segments 10 and 11. Lateral organs in segments 6-12, the first pair in form of rounded pits surrounded by glands. Fertile region in males and females beginning in segment 10. No oviducts.

Size:
Up to 7.5 mm for 47 segments.

Colour:
Transparent; without pigmentation.

Habitat:
Fine to coarse sand in sublittoral areas up to the low water level of the intertidal zone.

Distribution:
North Sea (Helgoland), English Channel, Skagerrak, Mediterranean.

Protodrilus gracilis