Hyalopomatus Marenzeller, 1878: 393, 394.
Hyalopomatopsis Saint-Joseph, 1894: 224, 261.
Cystopomatus Gravier, 1911: 315, 316.
EMENDED DIAGNOSIS. — Six thoracic chaetigers, 5 with uncini. Collar chaetae with either uniform (undifferentiated) limbate blade or with a proximal fin more or less separated from distal limbate blade. No Apomatus - type chaetae. Thoracic and abdominal uncini rasp-shaped. Abdominal chaetae geniculate or recurved, not always present in anterior segments. Soft vesicular operculum, with or without a differentiated distal opercular cape borne on a thin apinnulate opercular peduncle, or, no operculum at all present. Thoracic membranes short.
Tube white, small-sized (0.2 to 1.0 mm in width) sensibly isodiametric for most of its length. Proximal part weakly and discontinuously encrusting substrate, more or less curved, or roughly coiled and folding on itself, circular in cross-section, rarely semicircular or triangular. Distal part straight and rising from the substrate for a sizeable length, always circular in cross-section. Tube wall thin and brittle.