Coral, A Simple Animal Explained Simply

Appearing in the fossil record more than 400 million years ago, corals nearly vanished multiple times, with major disappearances at the end of the Permian (~252 Ma) and Cretaceous (~66 Ma) mass extinctions. Modern Scleractinian corals reappeared in the Triassic, facing further setbacks before thriving in the Cenozoic.

Corals exist at the tissue level, lacking organs, even a heart. On the evolutionary ladder, corals are one step above sponges. They are the simplest animals to have a nervous system, a connected muscular system, and a dedicated reproductive system.

Corals are sedentary animals collecting microscopic plankton passing by in ocean currents using their jelly-like tentacles or polyps. Each polyp secretes calcium carbonate, which builds up the hard structure or corallite housing. All corals live in fragile, shallow, warm, sunlit, salt-water environments that many other marine organisms depend upon.

1. Rough Star Coral (Isophyllastrea rigida) often called “rough cactus coral” is a rare, relatively small coral. They can be found in the Atlantic Ocean reefs along the shores of the Caribbeans, Bahamas, and Florida at depths of 3-65 feet (1-20 meters). Rough Star Corals arose during the Cenozoic Era beginning 65 million years ago.

• Rough Cactus Coral remains listed as threatened under the U.S. Engangered Species Act as of late 2025. Listed in 2014, it is protected due to declines from disease and rising ocean temperatures.

2. Elliptical Star Coral (Dichocoenia stokesi) often called “Pineapple Coral”, is named for its well-separated, oval or elongated corallites (stony cups from where the polyps protrude). Colors of living animals vary from yellowish-brown, cream, orange, and olive with white raised polyp corallite ridges. Elliptical Star coral is a colonial coral that forms a massive half-sphere dome or a flat, platform-like structure. This species can be found in the Caribbean, Florida and Gulf of Mexico to Venezuala regions in depths ranging from 3-130 feet (1-40 meters). The fossil records indicate they lived as far back as the Oligocene Era (34 to 23 million years ago).

• Elliptical Star Coral or Pineapple Star Coral is a fairly uncommon species which has been placed on the Red List for Endangered Species. In 1995, off the Florida Keys, it suffered from a disease called white plague, which killed 95% of its coral colonies. It’s a slow-growing variety struggling to come back but is fast diminishing unless humans do more about climate change.

3. Blushing Star Coral (Stephanocoenia michilenii) belongs to the coral family “Astrocoeniida” a colonial stony coral often recognized for extending its tentacles during the day, unlike most coral, and the ability to quickly retract them when disturbed, giving it a “blushing” appearance. Corallites (cups holding polyps) can be circular or polygonal. It can be found in Florida, the Caribbean and Central American regions, and as far south as Brazil in a wide range of depths from 3-330 feet (1-100 meters). Fossil records indicate they evolved in Atlantic reef ecosystems over 28 million years ago.

Blushing Star Coral is found in several reef habitats, including channels and lagoons and from shallow to mid-ocean depths. It grows massive colonies commonly boulder-like forms or mounds, to encrusting (low spreading growth forms that usually adhere to hard rocky surfaces) or form flattened domes reaching up to 2.5 feet in size.

• While not listed as endangered, Blushing Star Coral faces pressures from climate change, disease, and pollution in the Caribbean and tropical western Atlantic. 

4. Great Star Coral (Montastraea, cavernosa) forms sizable massive boulder-like heads that can grow to over 8 feet in diameter and also can form plate-like structures. Great Star Corals are characterized by large, thumb-sized, fleshy polyps that are distinct, conical, and often exhibit contrasting colors (green, orange, brown, or red). Montastraea, cavernosa coral is a dominant species at moderate depths 30–100 feet (9-30 meters) off Palm Beach County, Florida, and the windward shore of Barbados and the Caribbean. It also occurs in the Bahamas, the banks off the Texas coast, Bermuda, Brazil, and western Africa coastal waters. Great Star Corals have maintained a persistent prescence since the Mesozoic Era beginning in the Palogene Period approximately 60 million years ago.

• Great Star Coral is one of the deepest occurring corals found at depths from only a few meters to at least 295 feet (90 meters). Plate forms occur at the deepest depths.
• These colonial corals are crucial reef-builders that feed at night extending sweeper tentacles up to 8 inches long.

• As with all the star corals, the Great Star Corals are “hermatypic” producing stony calcium-carbonate skeletons developing a symbiotic relationship with algae called zooxanthellae that help nourish it, provide oxygen, and dispatch waste.
• This coral occasionally has a fluorescent red or orange color during the daytime.
• Some colonies have been found to be 500 years old or more.

• While not on the endangered list, threats to Montastraea cavernosa include coral bleaching, ocean acidification, and coral disease, especially black band disease and white plague caused by global warming.

5. Boulder Star Coral (Orbicella, annularis formerly Monastraea annularis) co-occurs in abundance with its cousin species described above, the Great Star Coral (Montastraea cavernosa). Boulder Star Coral has dominated in the Caribbean Seas over its cousin species including in the fossil records from the end of the Mesazoic 60 million years ago. Orbicella annularis also is native to the tropical western Atlantic Ocean and the Gulf of Mexico. Boulder Star Corals grow into varying colony shapes from boulder-like domes to columns appearing like a sack of potatoes to plate forms in response to differing light conditions. It grows in varying depths from a few meters to 80 meters (260 feet) deep, much like its cousin.

• Boulder Star Corals, often called “old-growth trees of the sea,” have been around for centuries, with some colonies, such as those found on the Great Barrier Reef, estimated to be between 400 and over 600 years old.
• Boulder Star Coral and Great Star Coral are often found side-by-side in similar habitats and while they are not typically aggressive toward one another, like most corals, they will compete for space. The Great Star Corals have adapted longer sweeping tentacles that can sting to overtake the Boulder Star Coral.
• Boulder Star Corals are typically shades of brown, green, yellow-brown, or grey.

Boulder Star Coral (Orbicella annularis) Credit: snorkelstj.com

• Boulder Star Corals including Orbicella annularis, O. faveolata, and O. franksi) are listed as threatened under the U.S. Endangered Species Act (ESA). They have experienced dramatic declines—over 50% in the last 30 years—due to bleaching, disease, and ocean warming, causing them to shift from large colonies to smaller, less productive ones. 

The Massive Starlet Coral (Siderastrea siderea) form large boulder-shaped colonies on reefs and rocky substrates found in reef environments across the Caribbean, Gulf of Mexico, Florida Keys, Bahamas and Bermuda.

• Honoring my mother-in-law, Winkie, pictured above with my husband in 1983 while visiting Florida, where she gathered the coral collection that is now in my care.

The Family for both the Lesser Starlet Coral (Shown Below) and the Massive Starlet Coral (Shown Above) is “Siderastreidae” – meaning corallites are linked by flowing septa (vertical growth plates that support the polyps) having course margins that are fused in the center to give bicycle spoke shape or star-shaped groupings.

Starlet Coral Comparison Chart

Massive Starlet Coral (Above)	Lesser Starlet Coral (Below)
Usually dome shaped	Mostly encrusting flat or uneven
Large colonies up to a meter	Usually small colonies one foot across
Roundish corallites	Corallites somewhat angular asymmetrical
Shallow corallites	Slightly deeper pitted corallites
Smooth surface	Pitted surface
Uniform color	Contrasting dark centers
Pink, cream brown, grey	Whitish, grey, green, light brown
Depths from 32-131 feet (10-40 meters)	Typically shallow depths from 32-82 feet (10-25 meters)
Not tolerant of tidepools or silt	Tolerant of tidepools and silt

7. Lesser Starlet Corals (Siderastrea radians) are primarily a shallow-water, massive, tightly-packed coral that can appear as encrusting sheets or, in disturbed areas, as free-living mobile balls.They are commonly found in shallow tropical to subtropical waters of the western Atlantic Ocean, Caribbean Sea, Florida and Gulf of Mexico. They are highly adaptable, frequently inhabiting reef environments, rocky areas, and tide pools. 

• Massive Starlet Coral is listed as Critically Endangered on the IUCN Red List of Threatened Species. While formerly considered least concern, recent studies show significant population declines (up to 2.5 decades) due to disease and climate-related stressors. 
• Lesser Starlet Coral is not currently listed as endangered. It is generally considered a resilient species. 

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