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Phylum Cnidaria > Class Anthozoa > Subclass Alcyonaria/Octocorallia > Order Pennatulacea
Slender sea pen
Virgularia sp.*
Family Virgulariidae
updated Oct 2016
Where seen? Often mistaken for a stick stuck in the sand, this elegant colony of animals is commonly encountered on our Northern shores. On silty sand and mong seagrasses.

Features: Colony resembles narrow feather. 15-20cm long, slender, stiff 'stem'. With short thin leaf-like structures (1-2cm) that have no spikes on the edges. The leaves are symmetrically arranged on both sides of the 'stem',. Tiny feeding polyps (autozooids) with 8 branched tentacles emerge from these leaf-like structures when submerged. The autozooids are tubular and fused to adjacent autozooids for most of their length. When the polyps are contracted, they form little round bumps. The colony also has another kind of polyp that sucks in water (siphonozooids). These are found on the 'stem' between the leaves.

The 'stem' usually can only be seen on one side of the animal. On the other side, the leaf-like structures obscure the 'stem'. Often the stiff stick-like supporting axis may stick out of the fleshier 'stem'. The other end is a bulbous foot that is buried in the sand. Colours seen include red, maroon, orange, purple and white.

When exposed at low tide, the leaf-like structures are collapsed, while the stiff central primary polyp remains upright. So the colony looks like a thin stick stuck in the ground. Sometimes, the central stalk is retracted into the ground, resulting in a ruffle of secondary polyps left peeping out at the surface.

Cyrene Reef, Aug 13
Pen pals: Slender sea pens are recorded to harbour small creatures such as porcelain crabs, shrimps, brittle stars and small nudibranchs. The Painted porcelain crab (Porcellanella picta) have been spotted on the Red slender sea pen.

Cyrene Reef, Aug 13

*Species are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience of display

Slender sea pens on Singapore shores

Photos of Slender sea pens for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map

Primary polyp partially retracted
into the ground.

Beting Bronok, Aug 05

Secondary polyps on the leaf-like structures.

A pair of Painted porcelain crabs
on the sea pen.

Beting Bronok, Aug 05

Chek Jawa, Jun 06

Changi, Jul 06

Changi, Jul 09

Tuas, Oct 12
Photo shared by Loh Kok Sheng on flickr.

Tanah Merah, Aug 09
Photo shared by James Koh on his blog.

East Coast PCN, Apr 17
Photo shared by Loh Kok Sheng on facebook.

Seringat-Kias, Aug 12
Photo shared by Loh Kok Sheng on flickr.

St. John's Island , Apr 12
Photo shared by Loh Kok Sheng on his blog.

Pulau Semakau, Jan 10
Photo shared by Loh Kok Sheng on flickr.

Pulau Semakau, Aug 10
Photo shared by Neo Mei Lin on her blog.

Changi, Aug 11

Changi, Jul 12



  • Erhardt, Harry and Daniel Knop. 2005. Corals: Indo-Pacific Field Guide IKAN-Unterwasserachiv, Frankfurt. 305 pp.
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