(Esmark, 1874)
Description:
Body long and slender.
Prostomium broadly rounded, without eyes. Two ovoid antennae and two palps of same shape. Peristomium and apodous segment of same length as following chaetigers. Segments without cilia.
Parapodium with short, rounded prechaetal lobe; bilobed postchaetal lobe slightly longer; with oval distal lobe. One acicula. Dorsal and ventral cirri short, triangular. Chaetae of three kinds: 1) ~12 slender simple smooth hooks; 2) 9-17 compound chaetae with short, smooth hooked blades; 3) 2-3 simple smooth distally blunt, chaetae (O. geryonicola-parapodium).
Two small thread-like pygidial cirri (O. geryonicola-posterior end).
Mandibles X-shaped, with toothed anterior margins. Maxillary carriers fused to each other and to smooth hooked basal maxillae. 3 (adults) to 13 pairs of toothed plates (maxillae) (O. geryonicola-detail).
Size:
Up to 140 mm for several hundred segments.
Colour:
White to yellowish.
Habitat:
Parasitic in the gill chambers of the brachyuran crab Geryon tridens .
Distribution:
Skagerrak and Kattegat.