Phylum Echinodermata > Class Stelleroida > Subclass Asteroidea
Knobbly sea star
Protoreaster nodosus
Family Oreasteridae
updated Jan 14

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 seen on Chek Jawa and some of our undisturbed Northern and Southern Shores. Adults are usually seen in coral rubble areas, alone or widely spaced apart. These spectacular animals are the highlight of a shore trip!

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.

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.

What do they 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 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.

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.

Pulau Sekudu, May 04


White and pinkish
Pulau Sekudu, Dec 03



Brown and chocolate
Beting Bronok, Jul 05



Green
Cyrene Reef, May 11

Underside
Pulau Sekudu, May 04

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

Mouth.


With six arms.
Cyrene Reefs, Jan 09

With four arms.
Cyrene Reefs, Jan 09

Four-armed
Beting Bronok, Jul 03


Blue
Chek Jawa, Jul 08

Green
Changi, Jul 08

Without knobs on the arms!
Cyrene Reef, Nov 08


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


Sometimes seen in contorted shapes.
Beting Bronok, Jun 04

Juveniles are common on Cyrene Reef
Cyrene Reef, Apr 08

Papulae emerging on the upper surface

Knobbly sea stars on Singapore shores

Photos for free download from wildsingapore flickr

more photos of knobbly sea stars on Singapore shores

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

Links
References
www.flickr.com
FREE photos of sea stars. Make your own badge here.
links | references | about | email Ria
Spot errors? Have a question? Want to share your sightings? email Ria I'll be glad to hear from you!
wildfactsheets website©ria tan 2008