# 2.1 Basic Coral Biology

## Cnidaria Characteristics

* Cnidarians have two tissue layers separated by mesoglea, a single hole that functions as the mouth and anus, leading to gastrovascular cavity (incomplete gut) 
* The mouth is surrounded by tentacles capable of ingesting prey covered with nematocysts, produced by the specialized cells cnidocytes 
* Medusa or polyp form 
* Four classes: Hydrozoa (colonial hydroids & siphonophores), Scyphozoa (jellyfish), Anthozoa (corals, sea fans, anemones), Cubozoa (box jellies) 
* Radial symmetry 

## Anatomy of Coral 

<figure><img src="https://789240665-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FShvdx4K6BBMxfuVPr2NP%2Fuploads%2FX53LChSSpIYB1Gvci456%2FSP_CCRStructFig01.jpeg?alt=media&#x26;token=e7461112-62cf-416f-837b-1ec7c305be74" alt=""><figcaption></figcaption></figure>

Corals consist of three main parts, collectively referred to as the holobiont:&#x20;

1. T**he host coral tissue**; a ring of tentacles surrounding a single opening called the mouth which leads to the stomach.&#x20;
   1. [Mesoglea](https://www.sciencedirect.com/science/article/pii/B9780123850263000097) - The mesoglea is a gelatinous, noncellular connective tissue layer.&#x20;
   2. [Gastrodermis](https://www.sciencedirect.com/science/article/pii/B9780123847195001660): has glandular and phagocytic cells that digest and incorporate the nutrients.&#x20;
   3. [Cenosarc](https://oceanservice.noaa.gov/education/tutorial_corals/media/supp_coral01a.html): The cenosarc is a thin band of living tissue that connect individual polyps to one another and help make it a colonial organism.&#x20;
   4. [Mesentarial filaments](https://reefs.com/when-corals-spill-their-guts/) - used to capture and kill prey, and sting competitors
   5. Mucus Ciliary system - traps and ingest organic particles&#x20;
2. **The host coral skeleton**, made of calcium carbonate
   1. See [Morphology](https://taylor-lindsay.gitbook.io/tl-comps/2.-coral-biology/broken-reference) Section&#x20;
3. **The symbiotic organisms** living within the coral tissue&#x20;
   1. See [Symbiosis](https://taylor-lindsay.gitbook.io/tl-comps/2.-coral-biology/broken-reference) Section&#x20;

## Basic Taxonomy

* Phylum: Cnidaria
  * Subphylum: Anthozoa&#x20;
    * Class: Hexacorallia (Anthozoans with 6-sided symmetry)&#x20;
      * Order: Scleractinia (Stony Corals)&#x20;
      * Order: Actiniaria (Sea Anemones)&#x20;
    * Class: Octocorallia (Anthozoans with 8-sided symmetry)&#x20;
      * Order: Pennatulacea (Sea pens)
      * Order: Alcyonacea (Soft Corals/Gorgonians)&#x20;
  * Subphylum: Medusozoa (jellyfish & hydra)&#x20;

## Historical Study of Coral Reefs

* [History of the study of marine biology](https://www.marinebio.org/creatures/marine-biology/history-of-marine-biology/)
  * Early expeditions - James Cook (1720s-80s) & Charles Darwin  (1800s-80s) focused on the discovery of new species, defining ecological concepts, plotting oceanographic features
  * Establishment of scientific institutions - oldest marine lab in France in 1859, woods hole established in 1888&#x20;
  * Deep sea exploration - 1934 HMS challenger expedition: humans descending to depths, 1960 Mariana's trench expidition&#x20;
  * Scuba - introduced by Cousteau in the 50s-70s&#x20;
* Important Scientists
  * [ICRS Darwin Medal Recipients](https://coralreefs.org/awards-and-honors/darwin-medal/)&#x20;
  * Darwin, Earle, Carson, Cousteau&#x20;