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Phylum Echinodermata > Class Stelleroida > Subclass Asteroidea
Knobbly sea star
Protoreaster nodosus
Family Oreasteridae
updated Jul 2020
if you learn only 3 things about them ...
They are no longer common on all our shores.
They come in a wide variety of colours and knob patterns.
They use water to pump up their bodies. Don't remove them from water for too long.

Where seen? This huge and colourful sea star is sometimes on some of our undisturbed Northern and Southern Shores. Adults are usually seen in coral rubble areas, sometimes many individuals gathered together. These spectacular animals are the highlight of a shore trip! According to Marsh and Fromont, it is found on mud, sand, seagrass flats, sandy coral reef flats in Australia.

Features: Diameter with arms, adults to 30cm, juveniles 8-15cm. Hard, heavy body that is calcified. Arms long tapering to rounded tip, thick and triangular in cross-section. Although their arms appear stiff, these can bend quite extensively. When submerged tiny transparent finger-like structures (papulae) might be seen on the upperside. This species is generally identified by the single row of knobs along the upperside of the arms. The shape, colour and number of knobs may vary. Underneath, from grooves under the arms, emerge tube feet with sucker-shaped tips. These tube feet can be bright red or purple! Knobbly sea stars are mostly red, orange or brown, but sometimes white or pink ones are encountered. Blue or green ones are also sometimes seen.

The Nodulose sea star (Protoreaster nodulosus) can look very similar. They are difficult to tell apart with certainty in the field.

Knobbly sea stars are not venomous, although they are often brightly coloured and covered with dangerous-looking knobs, nodules and spines. They are also called the Giant Nodulated sea star, Horned sea star or Chocolate Chip sea star.

Pulau Sekudu, May 04

Tiny pedicellaria near the mouth.
Pink or purple tube feet.

Mouth.
What does it eat? According to Lane, it eats micro-organisms and scavenges on dead creatures. According to Gosliner, it probably feeds on sponges. According to Schoppe, it prefers to eat clams and snails but also eats sponges, soft corals and other invertebrates. According to Marsh and Fromont, it eats algae, biofilm growing on the ground and also scavanges dead animals.

According to Coleman the sea star hosts shrimps, scale worms, harlequin crabs and sea star crabs. Others report parasitic snails as well as. But these have not been observed on the Knobbly sea stars seen at low tide.

Eating a sand dollar?
Cyrene Reef, May 11
Photo shared by Marcus Ng on flickr.

Spawning posture?
Cyrene Reef, Aug 11

Spawning posture?
Cyrene Reef, Mar 12
Knobbly babies: Sometimes, submerged large adults are seen standing on tip toes during a highish tide or incoming tide. They are probably getting ready to release eggs and sperm simultaneously! More about this spawning posture on the Echinoblog. Juveniles are commonly seen on Cyrene Reef among seagrasses, as well as some of our other shores.

Status and threats: Knobbly sea stars are harvested from the wild for the live aquarium trade, often selling for only a few dollars. In captivity, they are unlikely to survive long without expert care. In the past, Knobbly sea stars were among the most common large sea stars of Malaya. They are now listed as 'Endangered' on the Red List of threatened animals of Singapore. Cyrene Reef is among the few places left in Singapore where they can be seen regularly.

On a hot day, may be contorted. It's attempting to cool off. It is not dying, there is no need to move it.
Beting Bronok, Jun 04

Juveniles are common on Cyrene Reef
Cyrene Reef, Apr 08

Papulae emerging on the upper surface


With six arms.
Cyrene Reefs, Jan 09

With four arms.
Cyrene Reefs, Jan 09

Four-armed
Beting Bronok, Jul 03


White and pinkish
Pulau Sekudu, Dec 03

Brown and chocolate
Beting Bronok, Jul 05

Green
Cyrene Reef, May 11


Blue
Chek Jawa, Jul 08

Green
Changi, Jul 08

Without knobs on the arms!
Cyrene Reef, Nov 08

Knobbly sea stars on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores


Changi, Jun 10

Photo shared by James Koh on his blog.

Changi, Jun 10

Photo shared by James Koh on his blog.

Changi, Sep 10

Photo shared by Neo Mei Lin on her blog.


Changi, Jun 10

Photo shared by Loh Kok Sheng on his blog.

Changi, Oct 20
Photo shared by Marcus Ng on facebook.


Changi Carpark 6, May 21

Photo shared byJonathan Tan on facebook.

Changi, Oct 20
Photo shared by Marcus Ng on facebook.


Chek Jawa, Oct 08
Photo shared by Toh Chay Hoon on flickr.

East Coast (PCN), Jun 16

Photo shared by Loh Kok Sheng on flickr.


East Coast Park, Jul 16

Photo shared by Loh Kok Sheng on his blog.

East Coast Park, Feb 16

Photo shared by Loh Kok Sheng on flickr.

East Coast Park, Feb 16

Photo shared by Loh Kok Sheng on flickr.


East Coast Park, May 21

Photo shared by Loh Kok Sheng on facebook.

East Coast Park (PCN), May 21

Photo shared by Vincent Choo on facebook.

East Coast Park (B), Jun 21

Photo shared by Loh Kok Sheng on facebook.


Berlayar Creek, Oct 15

Photo shared by Jonathan Tan on facebook.

Berlayar Creek, Oct 15

Photo shared by Jonathan Tan on facebook.
Berlayar Creek, Feb 20
Photo shared by Loh Kok Sheng on facebook.


St John's Island, Jan 20

Photo shared by Jianlin Liu on facebook..

Seringat-Kias, Aug 15

Photo shared by Loh Kok Sheng on flickr.

Seringat-Kias, Aug 15

Photo shared by Loh Kok Sheng on flickr.


Pulau Semakau South, Feb 16

Photo shared by Loh Kok Sheng on his blog.
   

Acknowledgements
With grateful thanks to Chim Chee Kong of the Star Trackers for identifying the sea stars.

Links
References
  • Loisette M. Marsh and Jane Fromont. Field Guide to Shallow Water Seastars of Australia. 2020. Western Australian Museum. 543pp.
  • Tan Yong How Jonathan, Ria Tan and Loh Kok Sheng. 31 Mar 2016. Juvenile knobbly sea stars on Singapore shores. Singapore Biodiversity Records 2016: 48-52
  • Genevieve Sew & Siti Maryam Yaakub. 31 July 2015. Knobbly seastar on the shores of Tanah Merah. Singapore Biodiversity Records 2015: 105
  • Lane, David J.W. and Didier Vandenspiegel. 2003. A Guide to Sea Stars and Other Echinoderms of Singapore. Singapore Science Centre. 187pp.
  • Didier VandenSpiegel et al. 1998. The Asteroid fauna (Echinodermata) of Singapore with a distribution table and illustrated identification to the species. The Raffles Bulletin of Zoology 1998 46(2): 431-470.
  • Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants and animals of Singapore. Nature Society (Singapore). 285 pp.
  • Schoppe, Sabine, 2000. Echinoderms of the Philippines: A guide to common shallow water sea stars, brittle stars, sea urchins, sea cucumbers and feather stars. Times Edition, Singapore. 144 pp.
  • Gosliner, Terrence M., David W. Behrens and Gary C. Williams. 1996. Coral Reef Animals of the Indo-Pacific: Animal life from Africa to Hawai'i exclusive of the vertebrates Sea Challengers. 314pp.
  • Chou, L. M., 1998. A Guide to the Coral Reef Life of Singapore. Singapore Science Centre. 128 pages.
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