Kathi writes about fossils and other earthly subjects, plus the natural fauna of Michigan, features in her community, poetry, and more.
Coral, A Simple Animal Explained Simply
Appearing in the fossil record more than 400 million years ago, 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.
They 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 corallites housing. All corals live in the fragile, shallow, warm, sunlit, salt-water environments that many marine organisms depend upon.
This article includes information and photos of 5 related modern Star Corals and 2 related Starlet Corals belonging to the below classifications. They begin to differ at the "family" level, followed by the genus and species. Included in the information of each species are the three remaining category descriptions.
- Kingdoms: Animalia
- Phylum: Cnidaria (Marine Group with Stinging Cells)
- Class: Anthozoa (Flower Animal - Reef Building)
- Subclass: Hexacorallia (Polygon Structures)
- Order: Scleratinia (Modern Species of Stony Coral)
1. Rough Star Coral
Rough Star Coral (Isophyllastrea rigida) is commonly found in the Atlantic Ocean along the shores of the Caribbean Islands, Bahamas, and Florida. The fossil skeleton sample above is part of a collection gathered in the 70s and 80s when my husband’s parents vacationed in Florida.
Winkie, my mother-in-law, pictured above with my husband at 3 years old, cheerfully collected coral skeletons adrift on the Florida beaches before protection laws forbid it. Now in my care, it has been my pleasure to research their origins and share some of them with you on the information highway, which she never knew about, but would have been very proud to share.
The living example of Rough Star Coral (Isophyllastrea, rigida) shown above left is recognized by its small dome-shaped colonies forming irregular polygon valleys on the surface. They also show fleshy polyps with a thin white line over the top of the polyp ridges. Living colonies of the Rough Star Coral range in varying degrees of color from brown, light green, pinkish to yellowish. Their corallites, the skeletal cup from where the polyps sit, are on the large side.
Rough Star Coral belongs to the family, Mussidae known for thick tissue. They originated during the Cenozoic Era beginning 65 million years ago.
I wanted to show one of the Rough Star Coral's relatives that possesses many similarities, the colorful Star Cup Corals (Mussidae, acanthastrea) shown above. They are from a different genera and are quite a showy breed with very meaty polyps, inhabiting the Indo-Pacific regions.
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2. Elliptical Star Coral
Elliptical Star Coral is named for its well-separated oval or elongated corallites. Colors vary from yellowish-brown, cream, orange, and greenish-brown with white raised polyp corallite ridges. Scientifically named, Dichocoenia, stokesi, shown above, is a massive colonial coral with a fossil record that reveals the species flourished in the Caribbean region 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 and has been placed on the Red List for Endangered Species. In 1995, off the Florida Keys, Dichocoenia, stokesi suffered from a disease called white plague, which killed 95% of its colonies. It's a slow-growing variety struggling to come back but is fast diminishing unless we humans do something about climate change.
Classification Elliptical Star Coral
Family: Meandrinidae (meandering form)
Genus: Dichocoenia (hump-forming or flattened corals with irregular calyces)
Species: stokesi (elliptical or pineapple star coral)
3. Blushing Star Coral
Blushing Star Coral (Stephanocoenia, michilenii) have tentacles commonly extended during daylight, unlike most coral. It rapidly retracts its polyps when touched, causing a slight color change, which gives this coral its common name, Blushing Star Coral. It can be found in Florida, the Caribbean and Central American regions, and as far south as Brazil.
It's found in several reef habitats, including channels and lagoons. It grows massive colonies to encrusting (low spreading growth forms that usually adhere to hard rocky surfaces), forming flattened domes, usually. Corallites (cups holding polyps) can be circular to polygonal.
- The Blushing Star Coral's earliest fossil record dates back to the Eocene between 55 and 33 million years ago.
- The Blushing Star Coral is one of many coral species susceptible to white plague type II, which exposes the skeleton by rapid tissue destruction and is also on the Red List of Threatened species.
Classification Blushing Star Coral
Family: Astrocoeniid (Small family made up of both reef-building and non-reef building genus, both with and without symbiotic zooxanthellae as well as both branching and encrusting species).
Genus: Stephanocoenia (Colonies are flattened, usually with regular, smooth surfaces. Corallites are small, and the wall between them may be relatively wide).
Species: michelinii (Blushing Star Coral)
4. Great Star Coral
From the Upper Jurassic to recent times, the Great Star Coral, Montastrea cavernosa, forms sizable massive heads and sometimes plate-like structures. The polyps can be quite variable in color, from green and brown to bright red. It's a dominant species at moderate depths off Palm Beach County, Florida, and the windward shore of Barbados.
It can also occur in the Caribbean, the Bahamas, the banks off the Texas coast, Bermuda, Brazil, and western Africa coastal waters. It's one of the deepest occurring corals found at depths from only a few meters to at least 90 meters (295 feet). Plate forms occur at the deepest depths.
Threats to Montastrea cavernosa include coral bleaching, ocean acidification, and coral disease, especially black band disease and white plague caused by global warming.
- As with all the star corals, the Great Star Corals are hermatypic, containing symbiotic 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.
- Dead Montastrea cavernosa form shallow marine sediments.
Great Star Coral Classification
Family: Montastraeidae (Generally spherical shaped grooved surfaces)
Genus: Montastraea (Forms Large Boulders)
Species: cavernosa (False Knob Coral )
5. Boulder Star Coral
The Boulder Star Coral (Orbicella annularis) co-occurs in abundance with its cousin species described above, Great Star Coral (M. cavernosa). The primary difference is that it dominates in the Caribbean Sea but is also native to the tropical western Atlantic Ocean and the Gulf of Mexico. It grows in depths from a few meters to 80 meters (260 feet) deep, much like its cousin.
- Competition between the cousin species has shown the Great Star coral to have adapted longer sweeping tentacles to attack its intruding cousin, the Boulder Star Coral.
Boulder Star Coral Classification
Higher Class: Montastraea (Generally spherical shaped grooved surfaces)
Family: Merulinidae (Reef Building Stony Coral)
Genus: Orbicella (Shallow-water, zooxanthellate species)
Species: annularis (Columnar form)
6. Massive Starlet Coral
I felt the need to honor my mother-in-law, Winkie, pictured with my husband in 1983 when she was visiting Florida, where she gathered the coral collection that's now in my care.
I chose to provide a comparison chart between the two starlet corals, the Massive Starlet Coral and the Lesser Starlet Coral, from my mother-in-law's collection. The chart will have all the fantastic information so you can be informed about them.
Family for both Lesser Starlet and Massive Starlet Corals:
- Siderastreidae – Meaning corallites are linked by flowing septa (vertical growth plates) having course margins that are fused in the center to give bicycle spoke shape or star-shaped groupings. The corallites have ill-defined walls formed from thickened septa.
Some of the descriptions in the comparison chart are observable in the fossil skeletons, while others are only observable through photographs, or for the underwater diving and snorkeling enthusiasts.
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
Corallites somewhat angular asymmetrical
Deeper pitted corallites
Contrasting dark centers
Pink, cream brown, grey
Whitish, grey, green, light brown
Depth from 40m (130ft) to 10m
Only shallow depths of about 10m (32ft)
Not tolerant of tidepools or silt
Tolerant of tidepools and silt
7. Lesser Starlet Coral
Another interesting way to identify them worth mentioning is the Lesser Starlet Coral often looks as though the colony is growing under the materials around it, unlike the Massive Starlet Coral.
- Rough star coral – Isophyllastrea rigida | Marine Species Identification Portal
- Dichocoenia stokesii (Elliptical Star Coral or Pineapple Coral) | University of the West Indies
- Blushing Star Coral | Encyclopedia of Life
- Great Star Coral | Mexican Fish
- Boulder Star Coral | NOAA Fisheries
- Massive Starlet Coral | Encyclopedia of Life
- Lesser Starlet Coral | Encyclopedia of Life
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2022 Kathi Mirto