Alcyonium digitatum
Encyclopedia
Alcyonium digitatum or dead man's fingers is a species
of soft coral
in the Alcyoniidae
family. It is found around the coasts of the northern Atlantic Ocean
.
s which form a crust. The individual polyps are white and translucent, and project from the leathery surface when feeding, giving the colony a furry appearance.
and the Bay of Fundy
. The polyps live in colonies attached to bedrock, boulders, stones and occasionally the shells of crab
s and gastropods. They are most plentiful in areas with strong water movement and where there is insufficient sunlight for algae to predominate. They are usually found in the sublittoral zone
down to about fifty metres. This coral is common around the coasts of Britain and Ireland where Alcyonium glomeratum
and Alcyonium hibernicum are also found but these are much rarer and misidentification is unlikely.
colonies are found. Colony growth occurs mainly in the first half of the year with the polyps becoming inactive in late summer, and the base tissue turning reddish or brownish due to the growth of algae and hydroid
s on the surface. At this time the gonads are developing and spawn
ing occurs in December and January. Fertilisation takes place externally and the embryos float for a few days before developing into free swimming larvae. Most of these soon settle on a suitable substrate and new polyps develop but a few may remain in the zooplankton
for some time and disperse over a wide area. Colonies have been known to live for twenty years.
The polyps feed at various times of the day with their tentacles extended. They are suspension feeders gathering plankton
from the water with the help of cilia, and absorbing oxygen
at the same time.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of soft coral
Alcyonacea
The Alcyonacea, or the soft corals are an order of corals which do not produce calcium carbonate skeletons. Soft corals contain minute, spiny skeletal elements called sclerites. Aside from their scientific utility in species identification, sclerites give these corals some degree of support and...
in the Alcyoniidae
Alcyoniidae
Alcyoniidae is a family of leathery or soft corals in the phylum Cnidaria.-Description:A colony of leathery coral is stiff, hard and inflexible. It is composed of tiny polyps projecting from a shared leathery tissue...
family. It is found around the coasts of the northern Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
.
Description
Dead man's fingers is a colonial coral forming clumps of yellow, white or cream-coloured fleshy masses of finger-like lobes. The surface layer include many scleriteSclerite
A sclerite is a hardened body part. The term is used in various branches of biology for various structures including hardened portions of sponges, but it is most commonly used for the hardened portions of arthropod exoskeletons....
s which form a crust. The individual polyps are white and translucent, and project from the leathery surface when feeding, giving the colony a furry appearance.
Distribution and habitat
Dead man's fingers is found along the Atlantic coasts of north west Europe from Portugal to Norway. The species also occurs in parts of Canada and the north eastern coast of the United States, the Gulf of MaineGulf of Maine
The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America.It is delineated by Cape Cod at the eastern tip of Massachusetts in the southwest and Cape Sable at the southern tip of Nova Scotia in the northeast. It includes the entire coastlines of the U.S...
and the Bay of Fundy
Bay of Fundy
The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...
. The polyps live in colonies attached to bedrock, boulders, stones and occasionally the shells of crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s and gastropods. They are most plentiful in areas with strong water movement and where there is insufficient sunlight for algae to predominate. They are usually found in the sublittoral zone
Neritic zone
The neritic zone, also called coastal waters, the coastal ocean or the sublittoral zone, is the part of the ocean extending from the low tide mark to the edge of the continental shelf, with a relatively shallow depth extending to about 200 meters...
down to about fifty metres. This coral is common around the coasts of Britain and Ireland where Alcyonium glomeratum
Alcyonium glomeratum
Alcyonium glomeratum or red sea fingers is a species of soft coral in the Alcyoniidae family. It is found around the southern and western coasts of Britain and Ireland.-Description:...
and Alcyonium hibernicum are also found but these are much rarer and misidentification is unlikely.
Biology
The colonies of dead man's fingers are nearly always either male or female, although a small number of hermaphroditeHermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
colonies are found. Colony growth occurs mainly in the first half of the year with the polyps becoming inactive in late summer, and the base tissue turning reddish or brownish due to the growth of algae and hydroid
Hydroid
-Marine biology:Hydroids are a life stage for most animals of class Hydrozoa, small predators related to jellyfish.-Botany:In mosses, hydroids form the innermost layer of the stem of long, colourless, thin walled cells of small diameter.The cells are dead and lack protoplasm.They function as water...
s on the surface. At this time the gonads are developing and spawn
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
ing occurs in December and January. Fertilisation takes place externally and the embryos float for a few days before developing into free swimming larvae. Most of these soon settle on a suitable substrate and new polyps develop but a few may remain in the zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
for some time and disperse over a wide area. Colonies have been known to live for twenty years.
The polyps feed at various times of the day with their tentacles extended. They are suspension feeders gathering plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
from the water with the help of cilia, and absorbing oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
at the same time.