Syllids are small annelids distinguished from other groups by the presence of the proventricle, a barrel-like muscular region in the anterior end of the animals, visible through the relatively translucent skin. They are one of the most common and diverse groups of annelids in marine benthic environments.
Members of Syllidae are generally small and slender annelids, measuring less than 100 mm long. They are very diverse and abundant in shallow water environments from hard to soft bottoms, and many species are associated to other organisms. Syllids may constitute more than half of the polychaete species in the benthos. They are distinguished from other polychaetes by the presence of a barrel-like muscular region of the anterior digestive tract known as the proventricle.
Capa M. Syllidae Grube, 1850. www.artsdatabanken.no/Pages/313960. Downloaded <year-month-day>.