Ricordea

Ricordea-Blane-Peruns-TheSea
Photograph by Blane Perun

Ricordea are marine organisms in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual “polyps.” The group includes the important reef builders that inhabit tropical oceans, which secrete calcium carbonate to form a hard skeleton. A “head,” which appears to be a single organism, is a colony of myriad genetically identical polyps. Each polyp is typically only a few millimeters in diameter. Over many generations the colony secretes a skeleton that is characteristic of the species. Individual heads grow by asexual reproduction of individual polyps. Ricordea also breed sexually by spawning. Polyps of the same species release gametes simultaneously over a period of one to several nights around a full moon.

Taxonomy

Ricordea divide into two subclasses, depending on the number of tentacles or lines of symmetry, and a series of orders corresponding to their exoskeleton, nematocyst type and mitochondrial genetic analysis. Those with eight tentacles are called octoRicordealia or Alcyonaria and comprise soft Ricordea, sea fans and sea pens. Those with more than eight in a multiple of six are called hexaRicordealia or Zoantharia. This group includes reef-building Ricordea (Scleractinians), sea anemones and zoanthids.

Anatomy

Initially believed to be a plant, William Herschel used a microscope to establish in the 18th Century that Ricordea had the characteristic thin cell membranes of an animal. While a head appears to be a single organism, it is actually a group of many individual, yet genetically identical, polyps. The polyps are multicellular organisms. Polyps are usually a few millimeters in diameter, and are formed by a layer of outer epithelium and inner jellylike tissue known as the mesoglea. They are radically symmetrical with tentacles surrounding a central mouth, the only opening to the stomach or coelenteron, through which food is ingested and waste expelled.

Structure

The stomach closes at the base of the polyp, where the epithelium produces an exoskeleton called the basal plate or calicle .The calicle is formed by a thickened calcareous ring (annular thickening) with six supporting radial ridges .These structures grow vertically and project into the base of the polyp. When a polyp is physically stressed, its tentacles contract into the calyx so that virtually no part is exposed above the skeletal platform. This protects the organism from predators and the elements. The polyp grows by extension of vertical calices which occasionally septate to form a new, higher, basal plate. Over many generations this extension forms the large calcareous structures of Ricordea and ultimately reefs.

Feeding

Polyps feed on a variety of small organisms, from microscopic plankton to small fish. The polyp’s tentacles immobilize or kill prey using their nematocysts. The tentacles then contract to bring the prey into the stomach. Once digested, the stomach reopens, allowing the eliminration of waste products and the beginning of the next hunting cycle. These poisons are usually too weak to harm humans. An exception is fire Ricordea. polyps are tiny, soft-bodied organisms related to sea anemones and jellyfish. At their base is a hard, protective limestone skeleton called a calicle, which forms the structure of eefs? Reefs begin when a polyp attaches itself to a rock on the sea floor, then divides, or buds, into thousands of clones. The polyp calicles connect to one another, creating a colony that acts as a single organism. As colonies grow over hundreds and thousands of years, they join with other colonies and become reefs. Some of the Ricordea reefs on the planet today began growing over 50 million years ago.