Poecilostomatoida are an order of copepods previously included in the Cyclopoida

Cyclopoida

Cyclopoida is an order of small crustaceans from the subclass Copepoda. Like many other copepods, members of Cyclopoida are small, planktonic animals living both in the sea and in freshwater habitats. They are capable of rapid movement...

.

Description

The classification of these copepods has been established on the basis of the structure of the mouth. In poecilostomatoids the mouth is represented by a transverse slit, partially covered by the overhanging labrum

Labrum (arthropod mouthpart)

The labrum is a flap-like structure that lies immediately in front of the mouth in almost all extant euarthropods, the general exception being provided by the probable chelicerate-relatives the pycnogonids. It has proved to be by far the most controversial of all arthropod head structures. It is...

 which resembles an upper lip. Although there is variability in the form of the mandible among poecilostomatoids, it can be generalized as being falcate (sickle

Sickle

A sickle is a hand-held agricultural tool with a variously curved blade typically used for harvesting grain crops or cutting succulent forage chiefly for feeding livestock . Sickles have also been used as weapons, either in their original form or in various derivations.The diversity of sickles that...

-shaped).

The antennules are frequently reduced in size and the antenna

Antenna (biology)

Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

e modified to terminate in small hooks or claws that are used in attachment to host organisms.

Life cycle

As with many crustaceans, larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

l development is metamorphic

Metamorphosis

Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...

 with immature forms differing greatly from those of adults. Embryos are carried in paired or single sacs attached to first abdominal somite (as seen in the illustration of the female Sapphirina darwinii

Sapphirina darwinii

Sapphirina darwinii is a species of parasitic copepod.-References:**...

above right).

Ecology

Most poecilostomatoid copepods are ectoparasites of saltwater

Seawater

Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...

 fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 or invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s (including among the latter mollusks and 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). They usually attach to the external surface of the host, in the throat-mouth cavity, or the gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s. One family of poecilostomatoid copepods, however, have evolved an endoparasitic mode of life and live deep within their hosts' bodies rather than merely attaching themselves to exterior and semi-exterior surface tissue

Tissue (biology)

Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

.

In addition to typical marine environments, poecilostomatoid copepods may be found in such very particular habitat

Habitat

* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

s as anchialine caves

Anchialine pool

An anchialine pool or pond is a landlocked body with a subterranean connection to the ocean. Anchialine pools are a feature of coastal aquifers which are density stratified, with the water near the surface being fresh or brackish, and saline water intruding from the coast below at some depth...

 and deep sea vents (both hydrothermal vents and cold seeps). Here, many primitive associated copepods belonging to the orders Poecilostomatoida and Siphonostomatoida

Siphonostomatoida

Siphonostomatoida are copepods of the order of the subclass Maxillopoda, inside the subphylum Crustacea. There are 42 recognised families:*Amaterasidae*Archidactylinidae*Artotrogidae*Asterocheridae*Brychiopontiidae*Caligidae*Calverocheridae...

 and have been found. Representatives of one Poecilostomatoida family have successfully made the transition to freshwater

Fresh Water

Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...

 habitats and host animals therein.

List of families

There are over sixty families

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 currently recognized within the group:

• Abrsiidae
• Anchimolgidae
• Anomoclausiidae
• Antheacheridae
• Anthessiidae
• Bomolochidae
  Bomolochidae
  Bomolochidae is a family of parasitic copepods, containing the following genera:*Acanthocolax Vervoort, 1969*Acantholochus Cressey, 1984*Bomolochus Nordmann, 1832*Boylea Cressey, 1977*Ceratocolax Vervoort, 1965...
  
  
• Bradophilidae
• Catiniidae
• Chondracanthidae
  Chondracanthidae
  Chondracanthidae is a family of parasitic copepods, comprising the following genera:*Acanthocanthopsis Heegaard, 1945*Acanthochondria Oakley, 1930*Acanthochondrites Oakley, 1930*Andreina Brian, 1939*Apodochondria Ho & Dojiri, 1988...
  
  
• Clausidiidae
  Clausidiidae
  Clausidiidae is a family of parasitic copepods of the order Poecilostomatoida, containing the following genera:*Cemihyclops Karanovic, 2008*Clausidium Kossmann, 1875*Conchyliurus Bocquet & Stock, 1957*Foliomolgus I. M. Kim, 2001...
  
  
• Clausiidae
  Clausiidae
  Clausiidae is a family of parasitic copepods of the order Poecilostomatoida.-External links:*, Tree of Life Web Project*...
  
  
• Corycaeidae
• Echiurophilidae
• Entobiidae
• Erebonasteridae
• Ergasilidae
  Ergasilidae
  Ergasilidae is a widespread family of copepods and comprises many species. The type genus is Ergasilus. With a few doubtful exceptions all ergasilids are parasitic on fishes.-Biology:...
  
  
• Eunicicolidae
• Euniciolidae
• Gastrodelphyidae
  Gastrodelphyidae
  Gastrodelphyidae is a family of parasitic copepods....
  
  
• Herpyllobiidae
• Intramolgidae
• Kelleriidae
• Lamippidae
• Lernaeosoleidae
• Lichomolgidae
• Lubbockiidae
• Macrochironidae
• Mesoglicolidae
• Myicolidae
• Mytilicolidae
• Nereicolidae
• Octopicolidae
• Oncaeidae
  Oncaeidae
  Oncaeidae is a family of copepods, containing the following genera:*Archioncaea Böttger-Schnack & Huys, 1997*Conaea Giesbrecht, 1891*Epicalymma Heron, 1977*Monothula Böttger-Schnack & Huys, 2001*Oncaea Philippi, 1843...
  
  
• Philichthyidae
• Philoblennidae
• Phyllodicolidae
• Pionodesmotidae
• Polyankyliidae
• Pseudanthessiidae
• Rhynchomolgidae
• Sabelliphilidae
• Saccopsidae
• Sapphirinidae
  Sapphirinidae
  Sapphirinidae is a family of parasitic copepods, containing the following genera:*Copilia Dana, 1849*Saphirinella Claus, 1863*Sapphirina J. Thompson, 1830*Terebellicola M. Sars, 1861*Vettoria C. B. Wilson, 1924...
  
  
• Serpulidicolidae
• Shiinoidae
  Shiinoidae
  Shiinoidae is a family of parasitic copepods. The first species in the family to be described was Shiinoa occlusa, a single immature female of which was discovered on the fish Scomberomorus commerson, and described by Kabata in 1968. A second species, S...
  
  
• Spiophanicolidae
• Splanchnotrophidae
• Synapticolidae
• Synaptiphilidae
• Taeniacanthidae
• Tegobomolochidae
• Telsidae
• Thamnomolgidae
• Tuccidae
  Tuccidae
  Tucca is a genus of parasitic copepods in its own family, Tuccidae, in the order Poecilostomatoida....
  
  
• Umazurcolidae
• Urocopiidae
• Vahiniidae
• Ventriculinidae
• Xarifiidae
• Xenocoelomatidae