Rhizocephala

Information about Rhizocephala

Rhizocephala

The crab Liocarcinus holsatus parasitised by a rhizocephalan of the genus Sacculina showing the externa (circled)

Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Maxillopoda
Subclass:	Thecostraca
Infraclass:	Cirripedia
Superorder:	Rhizocephala MÃ¼ller, 1862

Orders

Kentrogonida
Akentrogonida

Rhizocephala are peculiar barnacles, parasitic on decapod crustaceans. Their bauplan is uniquely reduced in an extreme adaptation to their peculiar lifestyle.

Morphology

Rhizocephalans are related to the more typical barnacles. This is unrecognisable from the adult forms, but can be seen by comparison of the larvae. As adults they lack appendages, segmentation, and all internal organs except gonads and the remains of the nervous system. Other than the minute naupliar stages, the only distinguishable portion of a rhizocephalan body is the externa or reproductive portion of adult females.

The name "Rhizocephala" means "root-heads" and describes the adult female, which consists of a network of threads penetrating the body of the host that resemble the root of a plant penetrating the soil.

Life cycle

A female nauplius settles on a host and metamorphoses as it penetrates the internal portion of the animal. It then ramifies, or grows in a similar manner to a root system, through the host, centering on the digestive system. Once mature, the female produces a sac-like externa on the abdomen of the host. The externa is immature until a male nauplius settles on it and fuses with it. The externa then produces two types of eggs: small ones that will become females and large ones that become males. Because the externa is located in the same location as the host's egg sac would be, the host treats it as if it were its own egg sac, and never molts again (crustaceans do not molt until they release their eggs or young from the brood pouch). This behaviour even extends to male hosts, which would never have carried eggs or young in a brood pouch, but care for the externa in the same way as females.

Classification

This article follows Martin and Davis in placing Rhizocephala as a superorder of Cirripedia and in the following classification of rhizocephalans down to the level of families:^[1]

Superorder Rhizocephala MÃ¼ller, 1862

Order Kentrogonida Delage, 1884
Lernaeodiscidae Boschma, 1928
Peltogastridae Lilljeborg, 1860
Sacculinidae Lilljeborg, 1860, such as Sacculina
Order Akentrogonida HÃ¤fele, 1911
Chthamalophilidae Bocquet-VÃ©drine, 1961
Clistosaccidae Boschma, 1928
Duplorbidae HÃ¸eg & Rybakov, 1992
Mycetomorphidae HÃ¸eg & Rybakov, 1992
Polysaccidae LÃ¼tzen & Takahashi, 1996
Thompsoniidae HÃ¸eg & Rybakov, 1992, such as Thompsonia

References

^ Joel W. Martin and George E. Davis (2001). An Updated Classification of the Recent Crustacea. Natural History Museum of Los Angeles County.

Sacculina
Thompson, 1836

Species

''S. andersoni
S. atlantica
S. bicuspidata
S. bourdoni
S. carcini
S. gerbei
S. gibbsi
S. gonoplaxae
S.
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Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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Arthropoda
Latreille, 1829

Subphyla and Classes

Subphylum Trilobitomorpha
Trilobita - trilobites (extinct)
Subphylum Chelicerata

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crustaceans (Crustacea) are a large group of arthropods, comprising approximately 52,000 described species ^[1], and are usually treated as a subphylum ^[2].
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Maxillopoda
Dahl, 1956

Sub-classes

Thecostraca (1,320 species)

Tantulocarida (1,200 species)

Branchiura (200 species)

Pentastomida (100+ species)

Mystacocarida (12 species)

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Thecostraca
Gruvel, 1905

Infraclasses

Facetotecta
Ascothoracida
Cirripedia
Thecostraca are a group of marine invertebrates containing about 1,320 described species.
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Cirripedia
Burmeister, 1834

Superorders

Acrothoracica
Thoracica
Rhizocephala
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea and is hence distantly related to crabs and lobsters.
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Fritz MÃ¼ller

Here in Brazil
Born March 31 1821

Died May 21 1897 (aged 76)
Brazil
Nationality German
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order (Latin: ordo, plural ordines) is a rank between class and family (termed a taxon at that rank). The superorder is a rank between class and order. Exact details of formal nomenclature depend on the Nomenclature Code which applies.
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Parasitism is one version of symbiosis ("living together"), a phenomenon in which two organisms which are phylogenetically unrelated co-exist over a prolonged period of time, usually the lifetime of one of the individuals.
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Decapoda
Latreille, 1802

Suborders

Dendrobranchiata
Pleocyemata
See text for superfamilies.

The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish,
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A body plan, or body form, is essentially the blueprint for the way the body of an organism is laid out. An organism's symmetry, its number of body segments and number of limbs are all aspects of its body plan.
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An adaptation is a positive characteristic of an organism that has been favored by natural selection.^[1] The concept is central to biology, particularly in evolutionary biology.
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larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians).

The larva can look completely different from the adult form, for example, a caterpillar differs from a butterfly.
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An appendage in the broadest sense is an additional or subsidiary part existing on, or added to, something which can generally still function if the appendage has never existed or is later provided or grown, or will still perform a primary function if the appendage is removed.
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Segmentation in biology refers to the division of some metazoan bodies and plant body plans into a series of semi-repetitive segments, and the question of the benefits and costs of doing so. As such, segmentation is related to the more general concept of modularity.
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The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, sperm and egg cells are gametes.
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nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. Prominent parts of a nervous system include neurons and nerves, which are used in coordination.
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A nauplius is the first larva of crustaceans. It consists of a head and a telson; the thorax and abdomen have not developed yet. It has three pairs of appendages with which it swims; these become, in the adult, the antennules, the antennae, and the mandibles.
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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 form or structure through cell growth and differentiation.
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The digestive system is the organ system that breaks down and absorbs nutrients that are essential for growth and maintenance. The digestive system includes the mouth, esophagus, stomach, pancreas, liver, gallbladder, duodenum, jejunum, ileum, (intestines), rectum, and anus.
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In most birds and reptiles, an egg (Latin ovum) is the zygote, resulting from fertilization of the ovum. To enable incubation the egg is usually kept within a favourable temperature range as it nourishes and protects the growing embryo.
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Ecdysis is the moulting of the cuticula in arthropods and related groups (Ecdysozoa). Since the cuticula of these animals is also the skeletal support of the body and is inelastic, it is shed during growth and a new, larger covering is formed. The old skin is called an exuvia.
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A marsupium is the Latin word for a (brood) pouch in several animal groups.

Pouch (marsupial), in marsupials
Brood pouch (Peracarida), in peracarid crustaceans
Brood pouch (Syngnathidae), in syngnathids such as sea horses

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Thompsonia

Thompsonia is a genus of barnacle which has evolved into an endoparasite on crabs. It spreads through the crab's body as a network of threads. It makes many egg capsules which emerge through joints in the crab's shell.
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Rhizocephala

Information about Rhizocephala

Morphology

Life cycle

Classification

References