Zancleidae is a family of

cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

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 and heavily discussed group. It has also been called Gymnoblastea and (with ...

. Genera: * '' Ctenaria'' Haeckel, 1879 * '' Halocoryne'' Hadzi, 1917 * '' Oonautes'' Damas, 1937 * '' Zanclea'' Gegenbaur, 1856 * '' Zanclella'' Boero & Hewitt, 1992

Defining characteristics

Zancleidae is a family of hydrozoans from the order

Hydrozoa Hydrozoa (hydrozoans; from Ancient Greek ('; "water") and ('; "animals")) is a taxonomy (biology), taxonomic class (biology), class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline wat ...

ns are a class from the phylum

Cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

, 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 Bilateria () is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left� ...

, 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

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s. 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 animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

. Other species display a preference toward different organisms, such as

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

s, and

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

. 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 (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

. 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) en ...

, 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 f ...

. 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

stolon In biology, a stolon ( from Latin ''wikt:stolo, stolō'', genitive ''stolōnis'' – "branch"), also known as a runner, is a horizontal connection between parts of an organism. It may be part of the organism, or of its skeleton. Typically, animal ...

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) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

. 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 heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

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 the Ancient Greek word (), meaning "the depths". ...

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 or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various sp ...

or infralittoral 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

{{Taxonbar, from=Q146085 Capitata Cnidarian families