Actinozoa
Encyclopedia
Actinozoa is an obsolescent term in systematic
zoology
, first used by Henri Marie Ducrotay de Blainville
in his Manuel d'Actinologie (1834) to designate animals the organs of which were disposed radially about a centre.
De Blainville included in his group many unicellular forms, sea anemone
s, coral
s, jellyfish
, hydroid polyps, echinoderm
s, polyzoa, and rotifera.
Thomas Huxley
afterwards applie the term in a restricted sense. He showed that within de Blainville's group, along with a number of heterogeneous forms, there was a group of animals characterized by being composed of two layers of cells comparable with the first two layers in the development of vertebrate animals. These he called Coelentera, and showed that they had no special affinity with echinoderms, polyzoa, etc. He further divided the Coelentera into a group Hydrozoa
, in which the sexually produced embryos were usually set free from the surface of the body, and a group Actinozoa, in which the embryos are detached from the interior of the body and escape generally by the oral aperture. Huxley's Actinozoa comprised the sea-anemones, corals and sea pen
s, on the one hand, and the Ctenophora (comb jellies) on the other.
Modern biology confirms Huxley's criticism of De Blainville's Actinozoa, and upholds Hydrozoa
, but it is now known that the Ctenophora are only distantly related to jellyfish and their relatives, so Huxley's Actinozoa and Coelentera are no longer used (though the name Actinozoa is occasionally applied to the Anthozoa
). Modern taxonomies place the comb jellies in their own phylum Ctenophora and the jellyfish, sea anemones, and Hydrozoa
together in the phylum Cnidaria
.
Systematic
Systematic is an American hard rock band from Oakland, California. They were one of the first signings to Metallica drummer Lars Ulrich's record label, The Music Company, via Elektra Records. The band released two studio albums before disbanding in 2004....
zoology
Zoology
Zoology |zoölogy]]), is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct...
, first used by Henri Marie Ducrotay de Blainville
Henri Marie Ducrotay de Blainville
Henri Marie Ducrotay de Blainville was a French zoologist and anatomist.Blainville was born at Arques, near Dieppe. In about 1796 he went to Paris to study painting, but he ultimately devoted himself to natural history, and attracted the attention of Georges Cuvier, for whom he occasionally...
in his Manuel d'Actinologie (1834) to designate animals the organs of which were disposed radially about a centre.
De Blainville included in his group many unicellular forms, sea anemone
Sea anemone
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...
s, coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
s, jellyfish
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
, hydroid polyps, echinoderm
Echinoderm
Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....
s, polyzoa, and rotifera.
Thomas Huxley
Thomas Huxley
Thomas Henry Huxley PC FRS was an English biologist, known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution....
afterwards applie the term in a restricted sense. He showed that within de Blainville's group, along with a number of heterogeneous forms, there was a group of animals characterized by being composed of two layers of cells comparable with the first two layers in the development of vertebrate animals. These he called Coelentera, and showed that they had no special affinity with echinoderms, polyzoa, etc. He further divided the Coelentera into a group Hydrozoa
Hydrozoa
Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...
, in which the sexually produced embryos were usually set free from the surface of the body, and a group Actinozoa, in which the embryos are detached from the interior of the body and escape generally by the oral aperture. Huxley's Actinozoa comprised the sea-anemones, corals and sea pen
Sea pen
Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 14 families within the order; they are thought to have a cosmopolitan distribution in tropical and temperate waters worldwide...
s, on the one hand, and the Ctenophora (comb jellies) on the other.
Modern biology confirms Huxley's criticism of De Blainville's Actinozoa, and upholds Hydrozoa
Hydrozoa
Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...
, but it is now known that the Ctenophora are only distantly related to jellyfish and their relatives, so Huxley's Actinozoa and Coelentera are no longer used (though the name Actinozoa is occasionally applied to the Anthozoa
Anthozoa
Anthozoa is a class within the phylum Cnidaria that contains the sea anemones and corals. Unlike other cnidarians, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some substrate on which the cnidarian grows...
). Modern taxonomies place the comb jellies in their own phylum Ctenophora and the jellyfish, sea anemones, and Hydrozoa
Hydrozoa
Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...
together in the phylum Cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
.