Wikipedia
Erinaceusyllis, previously known as Sphaerosyllis (Claparède, 1863), is a genus belonging to the phylum Annelida, a group known as the segmented worms. This genus consists of several species that were previously described as Sphaerosyllis and as Sphaerosyllis erinaceus sub-species, differing by the compound chaetae.
In 2005, San Martín argued these differences were sufficient to consider them as different species, trigerring a taxonomic rediscription of the Syllidae, and describing this genus, Erinaceusyllis. Erinaceusyllis is similar to Sphaerosyllis. Species of Sphaerosyllis, however, always exhibit papillae on the pharyngeal opening, their pharyngeal tooth is conical and is always located on or very near to the anterior margin of the pharynx. They usually count with a short proventricle, itself provided with large muscle cell rows, large posterior acicula (which is distally bent at 90°), blades of compound chaetae which are short and unidentate, and offspring developing ventrally, females without capillary notochaetae, only present on males. Sphaerosyllis horrockensis, Sphaerosyllis belizensis, and Sphaerosyllis centroamericana were transferred to Erinaceusyllis under these distinguishing characteristics. At the same time, Prosphaerosyllis is close to Erinaceusyllis, but its species' pharyngeal teeth are rhomboidal to oval and located near the middle of their pharynges; also their antennae are short, tentacular and their dorsal cirri have a bulbous cirrophore and retractile cirrostyle. Their papillae are larger in number and of different sizes.