The presence of a caruncle in the polychaete family Sabellidae is documented. It is placed dorsally above the mouth, between the dorsal lips, supported with hyaline cartilage constituted by a homogeneous eosinophilic matrix and it is innervated directly from the cerebral ganglion. The caruncle surface has four longitudinal ciliated bands; the cilia from the lateral bands are hypertrophied, wider distally, tongue-like, forming a ciliated curtain or membranella. The genus
Megalomma is emended based on the presence of a caruncle, a long dorsalmost radiolar pair, a high number of radiolar skeletal cells, and the presence of interramal eyespots. We describe a new species from Acapulco in the Tropical Eastern Pacific –
Megalomma carunculata sp. nov. It has a caruncle, subtriangular ventral lappets, well developed dorsal pockets, compound eyes in all radioles, and interramal eyespots in the thoracic and abdominal segments.