Amphionides
Encyclopedia
Amphionides reynaudii is the sole representative of the order
Amphionidacea, and is a small (less than one inch long) plankton
ic crustacean
found throughout the world's tropical ocean
s, mostly in shallow waters.
, Amphionides is somewhat unusual, with many body parts being reduced or absent. For example, it has only one pair of mouthparts – the maxilla
e – the mandible
s and maxillules being vestigial.
Males and females differ in the form of the antennae
, and also by the presence in males of the eighth thoracic
appendage
, albeit in a reduced form. This is the site of the male gonopore
(the female's gonopore is on the sixth thoracic appendage). The first pleopod of the female is greatly enlarged and almost encloses the enlarged carapace
. This is assumed to be a chamber in which the eggs
are fertilised
and retained until hatching. The more streamlined carapace and pleopods of the male make it more hydrodynamic, and so fewer males are caught than females.
in the world's tropical oceans. It is plankton
ic, inhabiting waters near the sea's surface.
, Amphionides was originally thought to be a shrimp
. It was not until 1969 that the adult form was observed to be that described by Carl Wilhelm Erich Zimmer
in 1904, and only in 1973 was Amphionides placed in its own order by Donald I. Williamson
. The specific epithet reynaudii was given by Henri Milne-Edwards
in honour of a friend of his, possibly Count François Dominique Reynaud de Montlosier
. The generic name used by Milne-Edwards, Amphion, was invalid as a junior homonym of Amphion
Hübner, 1819, a genus of hawk moths
.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Amphionidacea, and is a small (less than one inch long) plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
found throughout the world's tropical ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
s, mostly in shallow waters.
Description
Amphionides grows to a length of 25 millimetre (0.984251968503937 in). MorphologicallyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
, Amphionides is somewhat unusual, with many body parts being reduced or absent. For example, it has only one pair of mouthparts – the maxilla
Maxilla (arthropod)
In arthropods, the maxillae are paired structures present on the head as mouthparts in members of the clade Mandibulata, used for tasting and manipulating food. Embryologically, the maxillae are derived from the 4th and 5th segment of the head and the maxillary palps; segmented appendages extending...
e – the mandible
Mandible (arthropod)
thumb|250px|The mandibles of a [[Bull ant]]The mandible of an arthropod is either of a pair of mouthparts used for biting, cutting and holding food. Mandibles are often simply referred to as jaws. Mandibles are present in the extant subphyla Myriapoda , Crustacea and Hexapoda...
s and maxillules being vestigial.
Males and females differ in the form of the antennae
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....
, and also by the presence in males of the eighth thoracic
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...
, albeit in a reduced form. This is the site of the male gonopore
Gonopore
A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects have a single common gonopore, except mayflies, which have a pair of gonopores...
(the female's gonopore is on the sixth thoracic appendage). The first pleopod of the female is greatly enlarged and almost encloses the enlarged carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
. This is assumed to be a chamber in which the eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are fertilised
Fertilisation
Fertilisation is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo...
and retained until hatching. The more streamlined carapace and pleopods of the male make it more hydrodynamic, and so fewer males are caught than females.
Distribution and ecology
Amphionides reynaudii has a cosmopolitan distributionCosmopolitan distribution
In biogeography, a taxon is said to have a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans. Other examples include humans, the lichen...
in the world's tropical oceans. It is plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic, inhabiting waters near the sea's surface.
Classification
Originally described from its larvaeCrustacean larvae
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow...
, Amphionides was originally thought to be a shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
. It was not until 1969 that the adult form was observed to be that described by Carl Wilhelm Erich Zimmer
Carl Wilhelm Erich Zimmer
Carl Wilhelm Erich Zimmer was a German zoologist specialising in crustaceans, especially the order Cumacea. He worked in Berlin, and is the taxonomic authority for the krill species Euphausia hanseni.-References:*....
in 1904, and only in 1973 was Amphionides placed in its own order by Donald I. Williamson
Donald I. Williamson
Donald Irving Williamson is a British planktologist and carcinologist, born 8 January 1922, Alnham, Northumberland, England. He gained his first degree from the Durham University in 1942, his Ph.D. from the same university in 1948, and a D.Sc. from the Newcastle University in 1972...
. The specific epithet reynaudii was given by Henri Milne-Edwards
Henri Milne-Edwards
Henri Milne-Edwards was an eminent French zoologist.Henri Milne-Edwards was the 27th child of William Edwards, an English planter and militia colonel in Jamaica and Elisabeth Vaux, a French. He was born in Bruges, Belgium, where his parents had retired. At that time, Bruges was a part of the...
in honour of a friend of his, possibly Count François Dominique Reynaud de Montlosier
François Dominique de Reynaud, Comte de Montlosier
Francois Dominique de Reynaud, Comte de Montlosier , was a notable French politician and political writer during the First French Empire, Bourbon Restoration and July Monarchy...
. The generic name used by Milne-Edwards, Amphion, was invalid as a junior homonym of Amphion
Amphion (moth)
Amphion is a genus of moths in the Sphingidae family....
Hübner, 1819, a genus of hawk moths
Sphingidae
Sphingidae is a family of moths , commonly known as hawk moths, sphinx moths and hornworms, that includes about 1,200 species . It is best represented in the tropics but there are species in every region . They are moderate to large in size and are distinguished among moths for their rapid,...
.