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Chironephthyra spp. [Image: After Wright and Studer, 1889, Gulf of Mexico Orgin, Waters, and Biota, Chapter 13, Page 321]
Octocorallians, or octocorals, are soft corals which are sedentary and colonial. Octocorals are comprised of soft corals, sea fans, sea whips, sea
feathers, sea pens, bamboo corals and precious corals. They are exclusively marine, present in all of the world's oceans from shallow, intertidal areas to over 6000 meters deep.
Each colony is comprised of several small polyps, with each polyp displaying a cylindrical and elongate body form. Octocorals are so named because they have eight-fold radial symmetry.
Scleractinia (Stony Corals)
Agaricia spp. [Image: After Moore, 1956, modified by F. Moretzsohn, Gulf of Mexico Origin, Waters, and Biota, Chapter 14, Page 333]
Scleractinia (hexacorals) are composed of stony corals. These corals are sedentary and polypoid; they are referred to as stony corals because each polyp is supported by an external aragonic (calcium carbonate) skeleton. These corals are sometimes referred to as hexacorals because they bear six (or multiples of six) pairs of internal mesenteries (divided chambers).
There are two main categories of Scleractinians: zooxanthellate and
non-zooxanthellate. Zooxanthellate are those that host symbiotic
photosynthetic algae; they are restricted to the photic zone within the
ocean, which occurs at depths of 80 meters or less. Non-zooxanthelate
Scleractinians occur in deeper, cooler waters up to 6000 meters deep.
Colonial Scleractinians are the primary reef formers in the world and live in the shallow waters of the tropics. Reef building corals undergo continuous asexual division. Other Scelractinian species undergo sexual reproduction.
This phylum includes a variety of organisms such as corals, jellyfish, sea anemones, and hydras. There are 13,000 Cnidarians worldwide, with 792 documented in the Gulf of Mexico. Cnidarians are ubiquitous in the marine environment occurring in all the world's oceans from shallow, intertidal areas to the deep ocean, with a few species that also exist in freshwater lakes and rivers.
Cnidarians have a very simple body form which consists of two thin layers of tissues, the ectoderm and endoderm, which is filled with a jelly-like substance made of cells and collagen fibers, called the mesoglea. All Cnidarians have cnidocysts, which are specialized cells used for trapping prey with a paralysis-inducing neurotoxin. Some Cnidarians utilize zooxanthella for food; which are symbiotic dinoflagellates that carry out photosynthesis inside the cnidarian, providing carbohydrates to the host.
Octocoral
(Muricea pendula)
[Photo: FGBNMS/National Undersea Research Center at UNC-Wilmington, Flower Garden Banks National Marine Sanctuary]
This discussion will look at two classes and one subphylum under Cnidaria: Anthozoa, Hydryozoa, and Medusozoa. Under the class Anthozoa, the two subclasses Octocorallia (soft
corals) and Scleractinia (stony corals) will be
discussed. Under the subphylum Medusozoa, the classes Cubozoa (box jellyfish) and Schyphyzoa ("true" jellyfish) will be discussed. The class Hydrozoa (hydroids) will also be discussed.
(Information from
Gulf of Mexico Origin, Waters, and Biota: Volume 1, Biodiversity,
Texas A&M University Press 2009).
Medusozoa [Image: After Mayer, 1906, Gulf of Mexico, Origin, Waters, and Biota, Chapter 18, Page 369]
The subphylum Medusozoa includes two important classes of jellyfish: Cubozoa (box jellyfish) and Scyphozoa. Most species in Medusozoa have two distinct life stages: hydroid and medusoid. The medusoid is the sexually reproductive life stage; this is the jellyfish-like appearing part of the life cycle and produces the life form with the bell shape and hanging tentacles. The medusa life stage is dominant in Scyphozoa and Cubozoa.
Cubozoans are voracious predators and when prey comes into contact with the nematocysts on their tentacles they paralyze the prey through injection of neurotoxins. Cubozoans are highly mobile and agile and they have complex eyes (but no brain). They have more of a cube shape than a bell shape and four tentacles.
Scyphozoans
have eight-fold raidal symmetry and live most of their life in the medusoid stage.
Hydrozoa (Hydroids)
Aglaophenia spp. [Image: After Brusca, 1980, modified by F Moretzsohn, Gulf of Mexico Origin, Waters, and Biota, Chapter 19, Page 383]
The class Hydrozoa is composed of creatures that are related to jellyfish but spend most of their lives in the sessile, polyp stage. As a result, they often resemble corals or seaweed more than jellyfish. Most hydrozoans are colonial and live in benthic habitats. They exist in all the oceans of the world and live in the shallow, intertidal areas out to deep ocean trenches. There are about 3400 documented species of Hydrozoa worldwide, with 214 recognized in the Gulf of Mexico.
In colonial hydrozoans the individual polyps may be highly differentiated for specific functions. One may exist exclusively for reproduction, while another in the colony may work to capture prey. The Portuguese man o' war is a well known hydroid in the family Siphonophorida, which exhibits colonial organization so advanced that they are often mistaken for a single jellyfish.
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