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