''Plexaurella nutans'', the giant slit-pore sea rod, is a tall

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of soft coral in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Plexauridae Plexauridae is a family of marine colonial octocorals in the phylum Cnidaria. Members of this family are found in shallow tropical and subtropical seas. Many species contain symbiotic photosynthetic protists called zooxanthellae. Characteristi ...

. It is a relatively uncommon species and is found in shallow seas in the Caribbean region.

Description

''Plexaurella nutans'' can grow to a height of over a metre (yard). It has thick cylindrical branches that occasionally fork and which are often slightly clubbed at the tips. These have a diameter of . The polyps are rather large and protrude from round, oval or slit-shaped grooves in the cup-shaped calyces in the coral skeleton. Each of these calyces is on a slight mound giving the coral a dimpled surface. When the polyps are extended, as they usually are, they give the coral a fuzzy appearance. The colour of this coral is usually pale brown, grey or sometimes lavender.

Distribution and habitat

''Plexaurella nutans'' is an uncommon species and occurs at depths down to in the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

, the

Bahamas The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to 88% of the ar ...

and

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

. It is usually found on isolated patch reefs or on forereef slopes.

Biology

The polyps of ''Plexaurella nutans'' extend their tentacles to feed on

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

and other small invertebrates floating past. The food gathered is shared with neighbouring polyps via the

gastrovascular cavity The gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Coelenterates or cnidarians (including jellyfish and corals) and Platyhelminthes (flatworms). The cavity may be extensively branched into a ...

inside the coral's skeleton. After particles of

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

marked with a

radioactive tracer A radioactive tracer, radiotracer, or radioactive label is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by ...

were fed experimentally to a single polyp, radioactivity was detected in tissues up to away. ''Plexaurella nutans'' is a

zooxanthella Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus '' Sym ...

te species of coral with large numbers of symbiotic dinoflagellates from the genus ''

Symbiodinium : ''This is about the genus sometimes called Zoox. For the company, see Zoox (company)'' ''Symbiodinium'' is a genus of dinoflagellates that encompasses the largest and most prevalent group of endosymbiotic dinoflagellates known. These unicell ...

'' living in its tissues. These are photosynthetic algae that provide nourishment to their host while benefiting from the coral's waste products. It was found experimentally that different species of ''Symbiodinium'' were found at different depths in ''Plexaurella nutans'' and other corals. If the corals' tissues were cultured in the laboratory, other species again became apparent, the growth of which was favoured by the laboratory environment. These must have been undetected in the tissues previously.

References

{{Taxonbar, from=Q3272474 Plexauridae Corals described in 1860