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Peanut worms
Phylum Sipuncula
updated Feb 14

if you learn only 3 things about them ...
They are smooth unsegmented worms.
Common but rarely seen as they usually remain underground.
The introvert is one of the interesting parts of this worm.

Where seen? These pink smooth fat worms are sometimes seen on some of our shores. They are more commonly encountered in mangroves and on soft ground (silty or muddy). But also in sandy areas near seagrasses.

What are peanut worms? Peanut worms are unsegmented and belong to Phylum Sipuncula. There are about 300 known species of peanut worms.

Features: 5-10cm long. Peanut worms are burrowing worm-like creatures that are sometimes seen above the ground on all our shores. When contracted, their ridged skins looks like the texture of peanut shells. Most are only a few millimeters long. Some burrow in mud, while others hide in crevices or abandoned snail shells and even in tubeworm tubes. 'Siphunculus' means 'little tube'. What is unique to peanut worms is their introvert, a long tube on their front end.

This is attached to the rest of the body, called the trunk. Like the finger of a glove, the introvert can be turned completely inside the trunk or extend out of the trunk. The mouth is at the end of the introvert, surrounded with tentacles.

The tentacles are covered with cilia (tiny beating hairs) and mucous. Food particles are gathered with the tentacles and then either the entire introvert is withdrawn into the trunk and the food particles eaten, or cilia on the tentacles transfer the particles along tracts into the mouth. Using their introvert, peanut worms can collect food while their soft bodies remain safely hidden. Some also use their introvert to burrow. One species even uses its introvert to swim!

What do they eat? Most peanut worms eat detritus, most of them mopping it up from the surface. Others eat their way through the sand as they burrow, and process the edible bits in it. They have a J-shaped digestive tract with the anus in the middle of the body so that wastes are brought back up near the entrance of the burrow. One kind of peanut worm can actually pierce annelid worms and suck out their juices!

Peanut worm babies: Peanut worms have separate genders, releasing eggs and sperm simultaneously into the water for external fertilisation. Some have a free-swimming larval stage that can travel long distances. In others, the eggs develop directly into little peanut worms.

Human uses: Peanut worms were once so plentiful in Singapore that they were collected and fed to ducks.

Status and threats: Like other creatures of the intertidal zone, they are affected by human activities such as reclamation and pollution. Trampling by careless visitors can also have an impact on local populations.

Cyrene Reef, Apr 07



Pasir Ris, May 09


Pulau Sekudu, Jul 09
Photo shared by Marcus Ng on his blog.

Pulau Senang, Jun 10
Photo shared by Loh Kok Sheng on his flickr.

Peanut worms on Singapore shores
Photos for free download from wildsingapore flickr

Phylum Sipuncula recorded for Singapore
from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore
*from WORMS

  *Family Phascolosomatidae
  Phascolosoma arcuatum=**Phascolosoma (Phascolosoma) arcuatum

  Family Sipunculidae
  Dendrostomum signifer=*Themiste (Lagenopsis) lageniformis Themistidae (Family)

Phascolosoma arcuatum=**Phascolosoma (Phascolosoma) arcuatum Phascolosomatidae (Family)

Siphonosoma cumanense

Sipunculus nudus
Sipunculus robustus

  *Family Themistidae
  Dendrostomum signifer=*Themiste (Lagenopsis) lageniformis

Links
  • Peanut worm (Phylum Sipunculida) Tan, Leo W. H. & Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore Science Centre, Singapore. 160 pp.
  • Peanut Worm (Sipunculids) Ng, Peter K. L. & N. Sivasothi, 1999. A Guide to the Mangroves of Singapore II (Animal Diversity). Singapore Science Centre. 168 pp.
  • Peanut worms on Life on Australian Seashores by Keith Davey on the Marine Education Society of Australia website: an introduction to worms including sipunculids with explanations of the major parts of their bodies and their lifestyles, and fact sheet on a peanut worm found in Australia.

References

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