''Alcyonium digitatum'' or dead man's fingers is a
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
soft coral
Alcyonacea is the old scientific order name for the informal group known as "soft corals". It is now an unaccepted name for class Octocorallia. It became deprecated .
The following text should be considered a historical, outdated way of treatin ...
in the family
. It is found around the coasts of the northern Atlantic Ocean and other temperate waters such as the South Pacific.
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
sclerite
A sclerite (Greek language, Greek , ', meaning "hardness, hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instea ...
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.
[Encyclopedia of Marine Life of Britain and Ireland]
/ref>
Distribution and habitat
Dead man's fingers is found along the Atlantic coasts of north west Europe from Portugal to Norway, most recently being discovered in the uncharted waters of Jammerbugt bay off the north-west coast of Denmark by a 2020 seafloor mapping project led by explorer Klaus Thymann. The species also occurs in parts of Canada, northeastern coast of the United States, the Gulf of Maine
The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America. It is bounded by Cape Cod at the eastern tip of Massachusetts in the southwest and by Cape Sable Island at the southern tip of Nova Scotia in the northea ...
and the Bay of Fundy
The Bay of Fundy () is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine. It is an arm of the Gulf of Maine. Its tidal range is the highest in the world.
The bay was ...
and the northern waters of New Zealand.World Register of Marine Species
/ref> The polyps live in colonies attached to bedrock, boulders, stones and occasionally the shells of crab
Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...
s and gastropod
Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, freshwater, and fro ...
s. 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
The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth.
From the point of view of marine biology it forms a relatively stable and well-illuminated ...
down to about fifty metres.[ This coral is common around the coasts of Britain and Ireland where '']Alcyonium glomeratum
''Alcyonium glomeratum'' or red sea fingers is a species of soft coral in the family Alcyoniidae. It is found around the southern and western coasts of Britain and Ireland.
Description
Red sea fingers is similar in shape to '' Alcyonium digitatu ...
'' 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 hermaphrodite
A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic.
The individuals of many ...
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 alga
Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...
e and hydroids
Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish.
Some hydroids such as the freshwater '' Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds, ...
on the surface. At this time the gonads are developing and spawn
Spawn or spawning may refer to:
* Spawning, the eggs and sperm of aquatic animals
Arts, entertainment and media
* Spawn (character), a fictional character in the comic series of the same name and in the associated franchise
** ''Spawn: Armageddon' ...
ing occurs in December and January. Populations have been found to synchronize their gametogenesis and spawning activities.[ artnoll, R.G. (1975). The annual cycle of ''Alcyonium digitatum''. Estuarine, Coastal and Shelf Science 3: 71-78.] 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 feeder
Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a spec ...
s gathering plankton
Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
from the water with the help of cilia, and absorbing oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
at the same time.[
]
References
External links
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{{Taxonbar, from=Q593303
Alcyoniidae
Corals described in 1758
Taxa named by Carl Linnaeus