HOME

TheInfoList



OR:

The
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Argulidae, whose members are commonly known as carp lice or fish lice, are parasitic
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
s in the class Ichthyostraca. It is the only family in the
monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...
subclass Branchiura and the order Arguloida, although a second family, Dipteropeltidae, has been proposed.


Taxonomy

Branchiurans were once thought to be copepods but are now recognised as a separate subclass in the superclass Oligostraca due to their distinct morphological characteristics.Alan P. Covich, ... D. Christopher Rogers, in Ecology and Classification of North American Freshwater Invertebrates (Third Edition), 2010 There are approximately 170 species in four genera recognised in the family Branchiura. The centres of diversity are the
Afrotropical The Afrotropical realm is one of the Earth's eight biogeographic realms. It includes Sub-Saharan Africa, the southern Arabian Peninsula, the island of Madagascar, and the islands of the western Indian Ocean. It was formerly known as the Ethiopi ...
and
Neotropical The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone. Definition In biogeogra ...
realms.


Description

Branchiurans have a flattened,
oval An oval () is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas of mathematics (projective geometry, technical drawing, etc.), it is given a more precise definition, which may inc ...
body, which is almost entirely covered by a broad, oval carapace, four thoracic segments each with a pair of swimming legs, a pair of anterior compound eyes, and an unsegmented abdomen without appendages which ends in paired abdominal lobes separated by the medial anal cleft. They are compressed dorsoventrally and can vary in size from just a few millimetres to over long, with females usually somewhat larger than the males. The mandibles are generally toothed hooks in Branchiurans. The maxillules provide sucking capability, and in the genera ''Argulus, Chonopeltis,'' and ''Dipteropeltis'', the adults have a pair of suction cups that are from modified first maxillae. The genus ''Dolops,'' keeps the larval stages claw-like appendages into adulthood. It is still unknown whether the ancestral state of these organisms had suction discs or the hooked condition seen in ''Dolops'', although it is thought that the specialized suctions discs are a later product of evolution. Also, females tend to be larger than the males. Between the genera there are multiple distinction between the sexes. For example, males in ''Argulus'' and ''Chonopeltis'' possess secondary sexual modifications on legs 2–4. The sexes both have their own sexual reproductive organs on their abdomens. The females have a spermathecae, while the males have a pair of testes. Their
compound eye A compound eye is a Eye, visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidium, ommatidia, which are tiny independent photoreception units that consist of a cornea, lens (anatomy), lens, and p ...
s are prominent, and the mouthparts and the first pair of antennae are modified to form a hooked, spiny
proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...
armed with suckers, as an adaptation to parasitic life. They have four pairs of
thoracic The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main ...
appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...
s, which are used to swim when not attached to the host. Not much research has been done on the respiratory system, which lacks gills, but respiratory areas on the carapace and gas exchange through the fleshy abdomen has been suggested.


Distribution and habitat

Branchiurans are widely distributed throughout the world. Most species are found in Africa and South America, and none are found in Antarctica. In North America, the genus ''Argulus'' is the only one known to be found in freshwater ecosystems.


Behaviour and ecology


Parasitism

Branchiurans are
obligate {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym '' facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism ...
ectoparasites that are found primarily on marine and freshwater fish (only the genus Argulus occurs in marine environments), but can also be found on other aquatic organisms such as invertebrates, salamanders, tadpoles and alligators. Some species feed on the blood of their host, while others feed on mucus and extracellular material. Feeding is facilitated by distinct morphological adaptations ( see Anatomy). Branchiura are able to attach to hosts through two mechanisms, hooked maxillae (as seen in ''Dolops'') or suction disks. After engorging themselves, the parasites typically wait two to three weeks before feeding again. Mitigation of these parasites has been studied through the use of a treatment containing plant parts. From this study, it is thought that Tobacco leaf dust (containing nicotine) can safely and effectively eliminate adult Branchiurans from fish, although this may be specific to only ''Argulus bengalensis''.


Reproduction

Only the life cycle of freshwater forms of the genus ''Argulus'' is well known. Branchiurans are not permanently attached to their hosts, and leave them for up to three weeks to mate and lay eggs, and reattach behind the fish's operculum, where they feed on
mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...
and sloughed-off
scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number ...
, or pierce the skin and feed on the internal fluids. The eggs hatch into parasitic postnauplius larvae. While on their host, Branchiurans mate. The female holds the eggs in the thorax and in some species the eggs can be found inside the lobes of the carapace. The spermathecae on the female stores the sperm. In the genus ''Dolops,'' the males deposit a spermatophore onto the females. Once the eggs are fertilized the females leave the host organism to lay their eggs in rows on surfaces of plants, rocks, etc. Like the adults, the larvae are parasites on fish. They are opportunistic in selecting host species of fish, and females are motile in their pursuit of locality of egg-laying. ''Chonopeltis'' larvae appear to be less developed than those of the other genera. Members of one group of ''Argulus'' hatch as metanauplius-larvae, followed by a juvenile stage. Another ''Argulus'' group, and all known species of ''Dolops'', hatch as juveniles.Atlas of Crustacean Larvae
/ref>


Impact

Fish lice occasionally reach high enough densities to cause
fish kill The term fish kill, known also as fish die-off, refers to a localized mass mortality event, mass die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (200 ...
s in
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. Nelu ...
operations, or more rarely in wild populations of fish. They can also become abundant in aquaria, sometimes resulting in the death of ornamental fish.


References


External links

* * {{Authority control Crustacean families Carboniferous first appearances Arthropod subclasses