THE ANIMAL FILES

Christmas tree worm

Spirobranchus giganteus

Two little trees are feeding structures.

Christmas tree worms expose colourful spiral crowns above a protective tube. Cilia carry captured food towards the mouth, while the same radioles also exchange gases. The worm can withdraw and close the entrance with a specialised plug.[1]

Follow the evidence ↓
Christmas tree worm
Image: Nhobgood Nick Hobgood · Commons · CC BY-SA 3.0
Crowns with two jobs
Radioles feed and exchange gases.[1]
A tube in coral
The worm secretes a calcareous tube.[1]
Closing the entrance
An operculum plugs the withdrawn worm's tube.[1]

Crowns with two jobs

Each spiral consists of feather-like radioles with cilia. Small captured material travels towards the mouth rather than the whole animal leaving its tube to chase food. Respiration uses these exposed structures too, combining several functions at the water interface.[1]

A tube in coral

The tube lies embedded in a coral head. After the worm settles, tube formation and coral overgrowth can leave much of the animal hidden in the structure. What a diver sees is mostly the exposed crown, not the full segmented body.[1]

Closing the entrance

A modified radiole carries the operculum used when the worm retreats. The hard tube and closable entrance provide different parts of the protection. The host relationship is not fully understood, and contact between the operculum and coral can sometimes abrade living tissue.[1]

A COMMON MIX-UP

Are the visible spirals separate miniature plants?

No. They are specialised appendages of one tube-dwelling annelid worm.[1][2]

TRY A LITTLE REASONING

Why can the worm feed without leaving its tube?

Reveal the explanation

Exposed ciliated radioles capture and transport small food to the mouth.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Christmas tree worm (cited revision)
  2. NCBI Taxonomy — Spirobranchus giganteus

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