Sharp, W. D., and Clague, D. A., 2006. 50-Ma initiation of HawaiiEmperor bend records major change in Pacific plate motion.
Science, 313, 1281–1284.
Sleep, N. H., 1990. Hotspots and mantle plumes: some phenomenology. Journal of Geophysical Research, 95(B5), 6715–6736.
Smith, D. K., and Jordan, T. H., 1987. The size distribution
of Pacific seamounts. Geophysical Research Letters, 14,
1119–1122.
Tarduno, J. A., Bunge, H. -P., Sleep, N. H., and Hansen, U., 2009.
The bent Hawaiian-Emperor hotspot track: inheriting the mantle
wind. Science, 324, 50–53.
Van Ark, E., and Lin, J., 2004. Time variation in igneous volume
flux of the Hawaii-Emperor hot spot seamount chain.
Journal of Geophysical Research, 109(B11401), doi:10.1029/
2003JB002949.
Wessel, P., 2001. Global distribution of seamounts inferred from
gridded Geosat/ERS-1 altimetry. Journal of Geophysical
Research, 106(B9), 19431–19441.
Wessel, P., and Kroenke, L. W., 2007. Reconciling late neogene
Pacific absolute and relative plate motion changes. Geochemistry Geophysics and Geosystems, 8(Q08001), doi:10.1029/
2007GC001636.
Wilson, J. T., 1963. A possible origin of the Hawaiian islands. Canadian Journal of Physics, 41, 863–870.
Wolfe, C. J., Bjarnason, I. T., VanDecar, J. C., and Solomon, S. C.,
1997. Seismic structure of the Iceland mantle plume. Nature,
385(6613), 245–247.
Wolfe, C.J. et al., 2009. Mantle shear-wave velocity structure
beneath the hawaiian hot spot. Science, 326, 1388–1390.
Cross-references
Atolls
Plate Tectonics
Subsidence Hypothesis of Reef Development
Volcanic Disturbances and Coral Reefs
Volcanic Loading and Isostasy
OCTOCORALLIA
Katharina Fabricius
Australian Institute of Marine Science, Townsville,
QLD, Australia
Synonyms
Alcyonaria (this term is now rarely used). Common
names: Gorgonians; Octocorals; Sea fans; Sea pens; Sea
whips; Soft corals
Definition
Octocorallia (also known as octocorals, or in earlier times
“Alcyonaria”) are a subclass of the class Anthozoa, in the
phylum Cnidaria. They are sessile polyp-bearing animals
with a mobile larval phase that are only found in marine
systems. The distinguishing characteristic of this subclass
is that their polyps always bear eight tentacles (hence octocoral), which are usually (but not always) fringed along
both edges by one or more rows of pinnules. The gastrovascular cavities are typically subdivided by eight septa.
Introduction
Octocorals are a major component of the sessile benthic
fauna of many coral reefs. Like Scleractinian corals, they
are modular (colonial) organisms which develop through
asexual replication and specialization of polyps. In contrast to Scleractinian corals (the primary reef building
corals), most octocorals do not usually deposit a rigid calcium carbonate exoskeleton, and they therefore tend to
attach to reefs rather than contribute substantially to their
framework or to sedimentary deposits. However, there
are a number of exceptions that do contribute substantially
to framework accretion, sedimentary deposits, and sediment stabilization (see below).
Classification
Octocorallia are a subclass of the class Anthozoa, phylum
Cnidaria. Like other anthozoans, octocorals bear polyps
that consist of a tubular body, terminating in a mouth that
is surrounded by hollow tentacles. Unlike other anthozoans, octocoral polyps always bear eight tentacles, which
are usually fringed by rows of pinnules. Polyps are internally compartmentalized by eight mesenteries. The ectoderm of the tentacles contains simple nematocysts
(cnidae or stinging cells) that are unable to paralyze large
zooplankton or sting other larger animals. The ectodermal
and endodermal cell layers are often connected by
a relatively thick and cellular mesoglea, which often contains calcium carbonate sclerites and collagen. Most
octocorals are colonial, with the exception of one deepwater species with a single solitary polyp (Taiaroa
tauhou). A colony develops from a single founder polyp
by asexual propagation (polyp budding). The resulting
multiple polyps in a colony are often embedded into
coenenchymal tissue, but remain connected by canals
(solenia).
There is substantial taxonomic uncertainty associated
with Octocorallia. At present, the subclass is divided into
three orders (Figure 1):
Helioporacea
Pennatulacea (sea pens)
Alcyonacea (soft corals and gorgonians)
The Helioporacea are represented by a single species, the
blue coral, Heliopora coerulea (family Helioporidae) in
the Indo-Pacific, and the genus Epiphaxum (family
Lithotelestidae) in the Caribbean. H. coerulea has no calcium carbonate sclerites, instead colonies consist of
a massive aragonite skeleton perforated by wide cylindrical cavities containing the polyps, connected by narrow
solenial tubes.
The Pennatulacea (sea pens) presently distinguish
around 200 species in 32 genera (15 families; Williams,
1995, 1999). The body of pennatulaceans consists of
a single large primary polyp, called the oozooid, with
a basal fleshy peduncle for anchorage in soft substratum.
Through lateral budding of the upper body wall of the
oozooid (rachis), two types of secondary polyps are being
740
OCTOCORALLIA
Science, 313, 1281–1284.
Sleep, N. H., 1990. Hotspots and mantle plumes: some phenomenology. Journal of Geophysical Research, 95(B5), 6715–6736.
Smith, D. K., and Jordan, T. H., 1987. The size distribution
of Pacific seamounts. Geophysical Research Letters, 14,
1119–1122.
Tarduno, J. A., Bunge, H. -P., Sleep, N. H., and Hansen, U., 2009.
The bent Hawaiian-Emperor hotspot track: inheriting the mantle
wind. Science, 324, 50–53.
Van Ark, E., and Lin, J., 2004. Time variation in igneous volume
flux of the Hawaii-Emperor hot spot seamount chain.
Journal of Geophysical Research, 109(B11401), doi:10.1029/
2003JB002949.
Wessel, P., 2001. Global distribution of seamounts inferred from
gridded Geosat/ERS-1 altimetry. Journal of Geophysical
Research, 106(B9), 19431–19441.
Wessel, P., and Kroenke, L. W., 2007. Reconciling late neogene
Pacific absolute and relative plate motion changes. Geochemistry Geophysics and Geosystems, 8(Q08001), doi:10.1029/
2007GC001636.
Wilson, J. T., 1963. A possible origin of the Hawaiian islands. Canadian Journal of Physics, 41, 863–870.
Wolfe, C. J., Bjarnason, I. T., VanDecar, J. C., and Solomon, S. C.,
1997. Seismic structure of the Iceland mantle plume. Nature,
385(6613), 245–247.
Wolfe, C.J. et al., 2009. Mantle shear-wave velocity structure
beneath the hawaiian hot spot. Science, 326, 1388–1390.
Cross-references
Atolls
Plate Tectonics
Subsidence Hypothesis of Reef Development
Volcanic Disturbances and Coral Reefs
Volcanic Loading and Isostasy
OCTOCORALLIA
Katharina Fabricius
Australian Institute of Marine Science, Townsville,
QLD, Australia
Synonyms
Alcyonaria (this term is now rarely used). Common
names: Gorgonians; Octocorals; Sea fans; Sea pens; Sea
whips; Soft corals
Definition
Octocorallia (also known as octocorals, or in earlier times
“Alcyonaria”) are a subclass of the class Anthozoa, in the
phylum Cnidaria. They are sessile polyp-bearing animals
with a mobile larval phase that are only found in marine
systems. The distinguishing characteristic of this subclass
is that their polyps always bear eight tentacles (hence octocoral), which are usually (but not always) fringed along
both edges by one or more rows of pinnules. The gastrovascular cavities are typically subdivided by eight septa.
Introduction
Octocorals are a major component of the sessile benthic
fauna of many coral reefs. Like Scleractinian corals, they
are modular (colonial) organisms which develop through
asexual replication and specialization of polyps. In contrast to Scleractinian corals (the primary reef building
corals), most octocorals do not usually deposit a rigid calcium carbonate exoskeleton, and they therefore tend to
attach to reefs rather than contribute substantially to their
framework or to sedimentary deposits. However, there
are a number of exceptions that do contribute substantially
to framework accretion, sedimentary deposits, and sediment stabilization (see below).
Classification
Octocorallia are a subclass of the class Anthozoa, phylum
Cnidaria. Like other anthozoans, octocorals bear polyps
that consist of a tubular body, terminating in a mouth that
is surrounded by hollow tentacles. Unlike other anthozoans, octocoral polyps always bear eight tentacles, which
are usually fringed by rows of pinnules. Polyps are internally compartmentalized by eight mesenteries. The ectoderm of the tentacles contains simple nematocysts
(cnidae or stinging cells) that are unable to paralyze large
zooplankton or sting other larger animals. The ectodermal
and endodermal cell layers are often connected by
a relatively thick and cellular mesoglea, which often contains calcium carbonate sclerites and collagen. Most
octocorals are colonial, with the exception of one deepwater species with a single solitary polyp (Taiaroa
tauhou). A colony develops from a single founder polyp
by asexual propagation (polyp budding). The resulting
multiple polyps in a colony are often embedded into
coenenchymal tissue, but remain connected by canals
(solenia).
There is substantial taxonomic uncertainty associated
with Octocorallia. At present, the subclass is divided into
three orders (Figure 1):
Helioporacea
Pennatulacea (sea pens)
Alcyonacea (soft corals and gorgonians)
The Helioporacea are represented by a single species, the
blue coral, Heliopora coerulea (family Helioporidae) in
the Indo-Pacific, and the genus Epiphaxum (family
Lithotelestidae) in the Caribbean. H. coerulea has no calcium carbonate sclerites, instead colonies consist of
a massive aragonite skeleton perforated by wide cylindrical cavities containing the polyps, connected by narrow
solenial tubes.
The Pennatulacea (sea pens) presently distinguish
around 200 species in 32 genera (15 families; Williams,
1995, 1999). The body of pennatulaceans consists of
a single large primary polyp, called the oozooid, with
a basal fleshy peduncle for anchorage in soft substratum.
Through lateral budding of the upper body wall of the
oozooid (rachis), two types of secondary polyps are being
740
OCTOCORALLIA