Ryan Photographic - Sabellidae - Feather duster worms
Family Sabellidae
The family Sabellidae contains 1177 species in 76 genera (not trombones). Their common name of feather duster worms relates to their feathery gills which are also used for feeding. Most sabellids secrete a papery tube which is mixed with sand grains. When threatened they quickly withdraw into them. Most possess eyespots which are excellent at detecting movement and in some they might be able to form images (this is supposition on my part btw). Ragged edges to the gills of some suggest that occasionally they aren't quite quick enough.
Sabellids are found in all the world's oceans, typically in shallow waters but some live in the deep sea.
Other common names include peacock worms and fan worms.
Many of the animals in the photos below are identified only to family or genus. These worms are difficult to identify without specimens. Any identifications would be welcome.
Bispira brunnea Social featherduster worm

Bispira brunnea Social featherduster worms, Belize-3305

Bispira brunnea Sabellid featherduster worms, Belize-3306

Bispira brunnea Sabellid featherduster worms, Belize-3307

Bispira brunnea? Bahamas
 Sabellid Belize med res.jpg)
Bispira brunnea (maybe) Sabellid Belize
Bispira Featherduster worm

Bispira Featherduster worm Kri Eco, Raja Ampat IMG_8517
Bispira species

Bispira species Puerto Galera, Philippines IMG_8096
Bispira variegata Variegated feather duster worm

Bispira variegata Variegated feather duster Roatan IMG_2920

Bispira variegata, Variegated fan worm, Roatan IMG_2915
Branchiomma nigromaculata Spotted feather duster worm

Branchiomma nigromaculata Spotted feather duster worm 2 Belize

Branchiomma nigromaculata Spotted feather duster worm 3 Belize

Branchiomma nigromaculata, Spotted feather duster worm Belize
Hypsicomus species Ruffled feather duster

Hypsicomus species Ruffled feather duster, Roatan IMG_2890
Sabella sp Feather duster worm

Sabella sp Feather duster worm NZ
Sabellastarte Sp. Feather duster worm

Sabellastarte Feather duster worm, Magic Bay, Rao Island, Indonesia IMG_7847
Sabellastarte sp. Featherduster worm

Sabellastarte Featherduster worm, Kri, Raja Ampat, West Papua IMG_0547
Sabellastarte sp. Featherduster worm

Sabellastarte sp. Featherduster worm, Kri, Raja Ampat, West Papua IMG_0633
Sabellastarte indica Indian feather duster worm

Sabellastarte indica Indian feather duster worm, Raja Ampat IMG_1504
Sabellastarte sp.

Sabellastarte species Raja Ampat West Papua IMG_0490
Sabellastarte sp.

Sabellastarte sp., Kri Eco, Raja Ampat IMG_8675
Sabellastartes sp., Feather duster worm
Sabellastartes species, Feather duster worm, Puerto Galera, Philippines f1889977344
Unidentified Sabellid

Unidentified Sabellid, Milford Sound, New Zealand EPV0227
Unidentified fan worm

Unidentified Fan worm Sea of Cortez-6588
Unidentified fan worm

Unidentified fan worms Puerto Galera, Philippines IMG_5275

Unidentified fan worm Puerto Galera, Philippines IMG_8148

Unidentified fan worm Puerto Galera, Philippines IMG_8146
Click here for a video of these worms
Unidentified Fanworm

Unidentified Fanworm gill detail, Raja Ampat, West Papua IMG_3791. The black dots are almost certainly eyes.

Unidentified Fanworm gill detail, Raja Ampat, West Papua IMG_3792
Unidentified feather duster worm

Unidentified Feather duster worm, Raja Ampat, West Papua IMG_2350

Unidentified Featherduster worm gills, Raja Ampat, West Papua IMG_2353