Syllidae

Syllidae, commonly known as the necklace worms,[2] is a family of small to medium-sized polychaete worms. Syllids are distinguished from other polychaetes by the presence of a muscular region of the anterior digestive tract known as the proventricle.[3][4]

Syllidae
Syllis gracilis micrograph, showing the distinctive barrel-shaped proventricle
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Annelida
Clade:	Pleistoannelida
Subclass:	Errantia
Order:	Phyllodocida
Family:	Syllidae Grube 1850[1]
Synonyms
Levidoridae

Schizogamy in syllid polychaete

Syllid worms range in size from 2–3 mm (0.08–0.12 in) to 14 centimetres (5.5 in). Most syllids are benthic organisms that transition to a pelagic epitoke for reproduction. They are found in all regions of the ocean, from the intertidal zone to the deep sea, and are especially abundant in shallow water.[3][5]

They are found in a range of habitats, moving actively on rock and sandy substrates, hiding in crevices and among seaweeds, and climbing on sponges, corals, hydrozoans, seagrasses and mangroves. They are generalist feeders.[6] A young Syllid was one of the first worms to be found with pollen from seagrass in its stomach, making it a possible pollinator.[7]

The proventricle, Syllid worm's most distinctive anatomical feature, allows the worm to feed by sucking due to its pumping action. It also plays a role in hormone production, and thus the worm's sexual development.[4] The proventricle is composed of strirated muscle cells with the longest known sacromeres among animals.[8] The proventricle is usually visible through the body wall.[9]

Syllis ramosa was the first polychaete discovered to have a branching body plan.[10] Later, two species of Ramisyllis were discovered to have a branching body plan.