Zancleidae is a family of
cnidaria
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Their distinguishing feature is cnidocytes, specialized cells that th ...
ns belonging to the order
Anthoathecata
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular group. It has also been called Gymnobl ...
.
Genera:
* ''
Ctenaria''
Haeckel, 1879
* ''
Halocoryne''
Hadzi, 1917
* ''
Oonautes''
Damas, 1937
* ''
Zanclea
''Zanclea'' is a genus of hydrozoans belonging to the family Zancleidae.
The genus has cosmopolitan distribution.
Species
Species:
*'' Zanclea alba''
*'' Zanclea apicata''
*'' Zanclea apophysis''
*''Zanclea baudini''
*'' Zanclea bomala''
...
''
Gegenbaur, 1856
* ''
Zanclella''
Boero & Hewitt, 1992
Defining characteristics
Zancleidae is a family of hydrozoans from the order
Anthoathecata
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular group. It has also been called Gymnobl ...
.
Hydrozoans
Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialized ...
are a class from the phylum
Cnidarian
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Their distinguishing feature is cnidocytes, specialized cells that th ...
, which include jellyfish, sea anemones, and other invertebrates. Cnidarians are defined by their two distinct tissue layers and radial symmetry. These characteristics distinguish them from invertebrates of the clade
bilateria
The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and ...
, which possess bilateral symmetry in their adult or larval forms. Hydrozoans can be colonial or solitary organisms and are often very small on their own. Zancleidae polyps are arranged in colonies and range from 700-750 um in their medusa stage.
Currently, there are three main genera described as, Zanclea Gegenbaur, Halocoryne Hadzi, and Zanclella Boero & Hewitt. Within these three genera, there are around 42 accepted species.
Zancleids have a complicated taxonomic history, and new species are discovered fairly often due to a better understanding of the range of variation between organisms of this family.
Anatomy and morphology
Zancleidae are colonial organisms that live in symbiosis with other benthic
invertebrates
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
.
They are most commonly seen in association with cheilostomata
bryozoa
Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...
.
Other species display a preference toward different organisms, such as
bivalves
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
,
corals
Corals are marine invertebrates within the class (biology), class Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important C ...
, and
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
.
Some scientists believe that they serve as protection for their choice host organism, but others argue that their relationship can be
parasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
.
The colonies of zancleids are separated into small
polyps
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral (opposite to oral) end is ...
, which arise from
asexual reproduction
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
. Most species only have monomorphic polyps, designed for protection and feeding, but some other species have both gastrozooids and dactylozooids, which specialize in different roles.
Zancleidae attaches to the surface of their host by a thin root-like structure called a hydrorhiza. These organisms are
stolons
In biology, stolons (from Latin '' stolō'', genitive ''stolōnis'' – "branch"), also known as runners, are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external s ...
and are often found embedded into the skeleton of whatever organism they prefer to live with.
The polyps have a white-ish clear coloring and appear orange in some parts.
Just like all cnidaria, their tentacles are lined with cnidophores, that house harpoon-like stinging cells called
nematocysts
A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this c ...
. These tentacles are used as a defense for both themselves and their host.
All of the species experience polyp and medusa stages, which vary in length depending on the species and other external factors.
Gastrozooids are responsible for producing and releasing the medusa buds.
The medusae are spherical and sometimes appear greenish. These miniature jellyfish-like organisms can have either zero, two, or four tentacles depending on the species.
It is theorized that their number of tentacles can be tied to their relationship with their host organism.
During the medusa stage, the zancleids feed on small organisms in their proximity, and eggs are released into the water column. These eggs will then be fertilized and will help to facilitate the growth of new colonies.
Ecological role
Gastrozooids specialize as the feeding mechanism within the zancleidae colonies. They are said to feed on the bryozoan
lophophore
The lophophore () is a characteristic feeding organ possessed by four major groups of animals: the Brachiopoda, Bryozoa, Hyolitha, and Phoronida, which collectively constitute the protostome group Lophophorata.[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 ...]
from the surrounding water.
The bryozoans, on the other hand, feed on phytoplankton, so there is no competition between the species.
In the medusa stage, the zancleids have been observed catching prey that they encountered by chance. The prey would then be immobilized by the tentacles and moved into the mouth cavity of the organism.
For colonies that prefer to live in association with corals, their presence in the community plays a role in the functionality of their surrounding ecosystem.
Distribution
Zancleidae has a wide-ranging distribution and has been discovered in a number of different places in the world's oceans. Many studies focusing on these organisms examined ones living in the Maldives and the Red Sea, but they have also been identified in the Indian ocean and throughout the Pacific.
Since their distribution underwater is connected to that of their hosts, they are found primarily in
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
environments. Some are also said to only appear in conjunction with their host when that organism has grown to a certain size. In terms of distribution within the benthic environment, bryozoans, the most common host for zancleids, have been seen to express a preference for shaded habitats in the
intertidal
The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of Marine habitat, habitats with var ...
or
infralittoral
The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal are ...
zones.
Taxonomic history
The phylogenetic origins of zancleidae are fairly unclear due to the lack of research. Very few studies have focused on compiling the DNA sequences of the different species, and it has also been difficult for scientists to find viable, fertile colonies to conduct their research on.
These factors severely limit the amount of work that can be done in relation to the classification of these organisms. It is accepted though, that convergent evolution with their hosts has driven speciation among the zancleidae family.
Many of these species have seen a large reduction in their polyp and medusa stages over the years, which helps support the theories of speciation.
It is also clear that differing numbers of tentacles distinguish species from each other, along with the presence of dactylozooids within the colonies.
The preference of host organism is another defining characteristic that is used as a means for classification between species.
References
Capitata
Cnidarian families
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