Comparing Two Starlet Corals

starlet fossil

Starlet Coral Fossil (Click to enlarge for fine details , then arrow back)

Starlet corals remains, not to be confused with star corals, are commonly found off the Caribbean, Florida and Bahama shores. I have two species from the genus Siderastrea. As I’ve mentioned in previous posts, these corals were discovered off Florida’s beaches in the 70’s and 80’s by my mother in law Winkie during family vacations.

Winky and Joe (83')

1983 Winkie Mirto with Son, Joseph (my late mother-in-law and husband)


Massive Starlet Coral (Siderastrea, sidereal )

Massive Starlet Coral (Siderastrea, sidereal )

Siderastrea, sidereal, commonly referred to as  Massive Starlet Coral is a very slow growing species that lives to a great age forming large colonies, sometimes, over a meter across. It’s closely related to the Lesser Starlet Coral, Siderastrea, radians. You must look very closely in order to observe their differences!

One way you can tell them apart is by their growth patterns. I’ve provided a comparison chart below. But another interesting way worth mentioning, first, is by observing the environment where they grow, which most people are only able to do through pictures. Nevertheless, unlike the Massive Starlet Coral, the Lesser Starlet Coral often looks as though the colony is  growing under the materials around it.

starlet coral radians

Lesser Starlet Coral (Siderastrea, radians Source:

starlet fossil -

Lesser Starlet Coral (Siderastrea, radians) Fossil

(Click to enlarge for fine details, then arrow back)

starlet fossil - underside

Lesser Starlet Coral (Siderastrea, radians) Fossil Underside


  • Kingdom: Animalia
  • Phylum: Cnidaria (Animals with Stinging Cells)
  • Class: Anthozoa (Flower Animal)
  • Subclass: Hexacorallia (Polygon Structures)
  • Order: Scleractinia (Modern Stony Corals)
  •  Family: Sideractinia
  • Genus: Siderastrea
  • Species: sidereal and radians






Massive Starlet Coral (Siderastrea, sidereal)               Lesser Starlet Coral (Siderastrea, radians)

  • Usually Dome Shaped                                                Mostly Encrusting Flat or Uneven Sphere
  • Large Colonies Up To A Meter                              Usually Small Colonies About 1 ft. Across
  • Roundish Corallites (Holes)                                    Somewhat Angular Asymmetrical Corallites
  • Shallow Corallites                                                        Deeper Pitted Corallites
  • Obscure Septa (Ridges)                                             Pronounced Septa (Ridges)
  • Thin Fine Walls Between Septa                             Wider Walls Between Septa
  • Septa Uniformly Separated                                     Septa Separated Unevenly
  • 50 to 60 Septa In Each Corallite                           30 to 40 Septa In Each Corallite
  • Smooth Surface                                                            Pitted Surface
  • Uniform Color                                                              Contrasting Dark Centers
  • Pink, Cream, Brown, Grey                                      Whitish, Grey, Green, Light Brown
  • Depth from 40 to 10 meters                                   Only Shallow Depths 10 meters
  • Not tolerant of tide pools and silt                         Tolerant of tide pools and silt

Comparing Two Star Coral Species

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 off western Africa.  It’s one of the deepest occurring corals found at depths from only a few meters to at least 90 meters.

Montastrea cavernosafossil

Montastrea cavernosa (The Great Star Coral) fossil


Monstastrea cavernosa (star coral) fossil side view

The fossil above is another in my possession from my late mother-in-law Winkie (Winifred) Mirto. She gathered a small collection off the Florida coast before protection laws forbid people to do so.

1983 Ft. Lauderdale Florida Winky and Joe

1983 Ft. Lauderdale Florida
Winkie and Joe

Threats to Montastraea cavernosa include coral bleaching, ocean acidification and coral disease, especially black band disease and white plague.

Choose Your Sunscreen Carefully

Montastraea are hermatypic, containing symbiotic algae called zooxanthellae that help nourish it, provides it oxygen and dispatch waste.

Montastraea, cavernosa with open tentacles source:

Montastraea, cavernosa with open tentacles


Kingdoms : Animalia

Phylum:  Cnardia (Marine group with stinging cells

Class:  Anthozoa (Flower Animal)

Order:  Scleratinia: (Modern species of Stony Coral)

Family:  Faviidae (Generally spherical shaped grooved surfaces)

Genus:  Montastraea

Species:  cavernosa (above) annularis (below)

Montasrea annularis

Montastrea annularis (Boulder Star Coral) fossil

Montastaea annularis commonly known as the Boulder Star Coral, co-occurs in near abundance with M. cavernosa only it dominates in the Caribbean regions. It also grows in varying depths down to 80 meters and grows in varying colony shapes (heads, column, or plates) in response to differing light conditions.


Montastraea annularis

Competition between the cousin genera has shown them to adapt longer sweeper tentacles in order to attack intruding corals.


Montastrea cavernosa Source:

Montastrea cavernosa