Knobbed Sea Star / Cushion Sea Star
Phylum: Echinodermata, Class: Asteroidea, Order: Valvatida, Family: Oreasteridae, Genus: Protoreaster, Species: Protoreaster nodosus · Oreasteridae (Cushion Star family) · Echinoderm exoskeleton (Note: While not technically a seashell, sea stars are frequently collected and included in shell collections as marine curiosities). Shape: Stellate (star-shaped).
Species
Protoreaster nodosus
Shell Type
Echinoderm exoskeleton (Note: While not technically a seashell, sea stars are frequently collected and included in shell collections as marine curiosities). Shape: Stellate (star-shaped).
Family
Oreasteridae (Cushion Star family)
Size
Approximately 6-8 inches across, which is typical for an adult specimen of this species. Adults generally range between 5 to 11 inches in diameter.
Color & Pattern
Muted brownish-yellow to tan coloration with prominent, darker rounded knobs or tubercles along the central disc and arms. The colors appear somewhat faded or sun-dried, typical of preserved specimens, lacking the vibrant reds or deep oranges found in live individuals.
Rarity
Common within its natural geographic range, though finding intact, well-preserved dried specimens on beaches depends heavily on local coastal collection laws and regional abundance.
Habitat
Inhabits shallow tropical waters, primarily sand flats, seagrass meadows, and coral rubble zones, typically found at depths ranging from the intertidal zone down to about 30 meters.
Geographic Range
Indo-West Pacific region, ranging from the Red Sea and East Africa across the Indian Ocean to Southeast Asia, Northern Australia, and the western Pacific islands.
Description
A striking five-armed echinoderm featuring a rigid, thick central disc adorned with prominent, blunt, knob-like spines. The texture is rough and calcified, characteristic of dried sea star tests, with tapering arms that radiate symmetrically from the central hub.
Key Features
Distinguished by the prominent, hard conical knobs or tubercles running along the upper surface of its arms and central disc, combined with a relatively thick body and five distinct, moderately tapering rays.
Collector Value
Low to moderate value. Commonly sold in seaside gift shops and shell stores as decorative curios. Exceptional, brightly colored live-collected specimens or unusually large sizes command slightly higher interest among marine life curio collectors.
Condition Notes
Dry, preserved specimen in fair to good condition. The structure is mostly intact with minimal arm tip damage, though the natural bright pigmentation has faded significantly due to drying and age. Collectibility grade: Good.
Interesting Facts
Unlike true shells (mollusks), sea stars possess a water vascular system used for locomotion and respiration. Protoreaster nodosus is heavily sought after for the curio trade, which has led to local population declines in certain heavily touristed regions.
Ecological Role
Acts as an important generalist predator and scavenger in benthic communities, feeding on detritus, sponges, and small benthic invertebrates, thereby helping to maintain the health and balance of shallow marine ecosystems.
Similar Species
Protoreaster linckii (Red-knobbed starfish), which features a brighter red-and-white coloration and sharper, more prominent contrasting red knobs.
Beach Finding Tips
In areas where they are native, dried tests are occasionally washed ashore following severe storms or strong tidal currents, though live specimens should never be removed from the water for collection.