Northern Star Coral (also known as Cup Coral or Ivory Bush Coral fragment)
Phylum: Cnidaria, Class: Anthozoa, Order: Scleractinia, Family: Rhizangiidae, Genus: Astrangia, Species: A. poculata · Rhizangiidae (Star Corals / Cup Corals) · Cnidarian Skeleton (Scleractinian Coral); specifically a colonial stony coral fragment. It is not a mollusk/shell in the traditional sense, but a calcium carbonate skeleton of a marine colony.
Species
Astrangia poculata (Confidence: 95%)
Shell Type
Cnidarian Skeleton (Scleractinian Coral); specifically a colonial stony coral fragment. It is not a mollusk/shell in the traditional sense, but a calcium carbonate skeleton of a marine colony.
Family
Rhizangiidae (Star Corals / Cup Corals)
Size
Approximately 0.75 to 1 inch (20-25mm) in length. This is a small fragment; colonies typically grow in encrusting patches ranging from 1 to 4 inches in diameter.
Color & Pattern
Base color is a creamy off-white to pale tan. The individual corallites (cups) show a radiating 'star' pattern formed by calcium septa. The surrounding matrix is porous and light brown, likely due to mineral staining or remaining organic matter. The appearance is natural and slightly weathered from surf action.
Rarity
Common; frequently found on North and South Carolina beaches, especially after storms or high tides that dislodge colonies from nearshore structures.
Habitat
A hardy species found in temperate marine waters from the intertidal zone down to 260 feet. It attaches to hard substrates like rocks, pilings, and larger shells (often found on Whelk or Oyster shells). Unlike tropical corals, it can survive in murky, cold water.
Geographic Range
Western Atlantic, ranging from Cape Cod, Massachusetts, down through the Gulf of Mexico and into the Caribbean. Very common along the South Carolina coast.
Description
A charming, calcified fragment of a stony coral colony. This specimen features several distinct, circular corallites (cups) where individual polyps once lived. Each cup contains delicate, radiating skeletal plates called septa that give the specimen a floral or celestial appearance. The fragment is encrusted on a thicker, stony base, showing the typical colonial growth form of the species.
Key Features
Distinct star-shaped cups (corallites) with visible septa, small size, and an encrusting growth habit. The cups are roughly 3-5mm in diameter. It lacks the massive, brain-like structure of tropical species, remaining relatively flat or slightly mounded.
Collector Value
Low monetary value ($1-$5), but high educational value. It is a prized find for beachcombers in the Carolinas who may not expect to find 'coral' in temperate waters. Desirability increases for large, complete colonies encrusted on beautiful shells.
Condition Notes
Fair to Good. The fragment is beach-worn, resulting in softened edges on the corallites. The structure is intact enough for identification, though some fine detail in the septa has been eroded by sand and surf. General collectibility is for educational/scientific interest.
Interesting Facts
Astrangia poculata is a 'facultative' coral, meaning it can live with or without symbiotic algae (zooxanthellae). This allows it to inhabit much colder and darker waters than typical tropical reef-building corals. It is a primary subject for scientists studying coral resilience to climate change.
Ecological Role
Provides micro-habitat for small invertebrates and contributes to the calcium carbonate structure of the seafloor. They are active predators, using stinging tentacles to catch microscopic plankton from the water column.
Similar Species
Oculina arbuscula (Ivory Bush Coral) which has more prominent, branching 'bush-like' stalks, and Balanophyllia floridana which is usually a solitary cup rather than a colony.
Beach Finding Tips
Look in the 'shell hash' or drift lines at low tide, particularly at Myrtle Beach after a period of rough surf. Scan for small, white, 'bony' looking objects that stand out against the darker sand and fragments of clam shells.
Notes
Myrtle Beach SC