Gonopod

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One of two gonopods of the greenhouse millipede (Oxidus gracilis). Scale bar: 0.2 mm or approximately 1/127 in Oxidus gracilis gonopod SEM.png
One of two gonopods of the greenhouse millipede (Oxidus gracilis). Scale bar: 0.2 mm or approximately 1/127 in

Gonopods are specialized appendages of various arthropods used in reproduction or egg-laying. In males, they facilitate the transfer of sperm from male to female during mating, and thus are a type of intromittent organ. In crustaceans and millipedes, gonopods are modified walking or swimming legs. Gonopods may be highly decorated with elaborate structures which may play roles in sperm competition, and can be used to differentiate and identify closely related species. Gonopods generally occur in one or more pairs, as opposed to the single (un-paired) reproductive organs such as the aedeagus of insects or the penis of harvestmen.

Contents

Insects

Paired gonopods (g) on the male genitalia of Corydalus cornutus Corydalus cornutus genitalia.png
Paired gonopods (g) on the male genitalia of Corydalus cornutus

In insects, gonopods are appendages of the genital segment that may be used in insemination, or that comprise the egg-laying apparatus. [1] [2]

Crustaceans

In male decapod crustaceans, gonopods are modified swimming appendages (pleopods). The anterior two pair of pleopods in males are modified for sperm transferring, with differing degree of morphological diversification. [3]

Millipedes

Gonopod diversity in 20 Chaleponcus species (Spirostreptida, Odontopygidae) from Tanzania Chaleponcus gonopods.png
Gonopod diversity in 20 Chaleponcus species (Spirostreptida, Odontopygidae) from Tanzania

In millipedes, gonopods consist of one or two pairs of often highly modified walking legs in mature males, and are primarily found in members of the subgroup Helminthomorpha—containing most orders and the vast majority of species—where they are located on the seventh body segment consisting of leg pairs 8 and/or 9. [4] Males of the subgroup Pentazonia (which includes the Oniscomorpha (pill millipedes) and Glomeridesmida) lack gonopods but possess enlarged appendages known as telopods at the rear of the body used to firmly hold females during mating. [5] The complex structure of gonopods is a primary method of distinguishing closely related species of millipede, [6] although the terminology used to describe the same structures may vary between authors. [7] The complex morphology of millipede gonopods may be driven by sperm competition or other forms of sexual selection, with some structures serving to scoop out or displace sperm of other males, and others acting to stimulate females into becoming sexually receptive. [5]

Millipede gonopods do not produce sperm directly, but rather gather sperm produced from a gonopore on the base of the third body segment. [8]

Gonopods develop gradually during the growth of an individual. In early developmental stages, all legs are of the walking type, and cannot be used to determine sex. Through successive molts, the walking legs metamorphose into mature gonopods. [8]

Gonopod development in Nopoiulus kochii (Julida, Blaniulidae). A: juvenile with walking legs on segment 7 (asterisk). B: subsequent stage with walking legs replaced by gonopod primordia. C: adult stage with gonopods (colored) in place of walking legs. Non-systemic metamorphosis in millipedes- Nopoiulus kochii.png
Gonopod development in Nopoiulus kochii (Julida, Blaniulidae). A: juvenile with walking legs on segment 7 (asterisk). B: subsequent stage with walking legs replaced by gonopod primordia. C: adult stage with gonopods (colored) in place of walking legs.
OrderNumber of pairs of
gonopods/telopods
Leg pair(s) modified! [lower-alpha 1] Notes
LP = Leg pair
Image [lower-alpha 2]
Callipodida 18thLP9 is reduced
Sinocallipus steineri Sinocallipus steineri gonopods.jpg
Sinocallipus steineri
Chordeumatida 28th & 9thGonopods and other accessory mating legs vary within the four suborders: In Chordeumatidea LP9 sperm-transferring, LP10 is reduced, and LP11 possess coxal glands; in Heterochordeumatidea LP9 sperm-transferring, LP10 reduced, and both LP10 and LP11 with coxal gland; in the Craspedosomatidea and Striariidea, LP8 sperm-transferring, LP9 modified, LP10 and LP11 with coxal glands
Glomerida 2 (telopods)Not involved with sperm transfer, only clasping females
Glomeris troglokabyliana walking legs (A, B) and telopod (C) Glomeris troglokabyliana telopods.png
Glomeris troglokabyliana walking legs (A, B) and telopod (C)
Glomeridesmida 1 (telopods)
Julida 28th & 9thLP9 sperm-transferring
Ommatoiulus chambiensis right anterior (1) and posterior (2) Ommatoiulus chambiensis, gonopod.png
Ommatoiulus chambiensis right anterior (1) and posterior (2)
Platydesmida 29th & 10thLeg-like; LP 9 sperm-transferring
Polydesmida 18th
Desmoxytes lingulata Desmoxytes lingulata gonopods.jpg
Desmoxytes lingulata
Polyxenida 0Indirect fertilization
Polyzoniida 29th & 10thleg-like; LP 9 sperm-transferring
Siphoniulida 18th
Siphonocryptida 29th & 10thleg-like, LP 9 sperm-transferring
Siphonophorida 29th & 10thleg-like; LP 9 sperm-transferring
Illacme plenipes, arrow pointing to anterior gonopods Illacme plenipes gonopods in situ.jpg
Illacme plenipes , arrow pointing to anterior gonopods
Sphaerotheriida 2 (telopods)
Sphaeromimus vatovavy posterior telopods Sphaeromimus vatovavy posterior telopods.jpg
Sphaeromimus vatovavy posterior telopods
Spirobolida 28th & 9thLP9 sperm-transferring, LP8 fused into single structure.
Aphistogoniulus jeekeli anterior (A) and left posterior (B) Aphistogoniulus jeekeli holotype gonopods 03.png
Aphistogoniulus jeekeli anterior (A) and left posterior (B)
Spirostreptida 28th & 9thLP8 sperm-transferring
Stemmiulida 18thLP8 sperm-transferring; LP9 reduced
  1. counting from head
  2. not necessarily representative of order

See also

Related Research Articles

Millipede class of arthropods

Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name being derived from this feature. Each double-legged segment is a result of two single segments fused together. Most millipedes have very elongated cylindrical or flattened bodies with more than 20 segments, while pill millipedes are shorter and can roll into a ball. Although the name "millipede" derives from the Latin for "thousand feet", no known species has 1,000; the record of 750 legs belongs to Illacme plenipes. There are approximately 12,000 named species classified into 16 orders and around 140 families, making Diplopoda the largest class of myriapods, an arthropod group which also includes centipedes and other multi-legged creatures.

Pedipalp Appendage on front of spider, crab, scorpion

Pedipalps are the second pair of appendages of chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") and anterior to the first pair of walking legs.

Isopoda order of arthropods

Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and five pairs of branching appendages on the abdomen that are used in respiration. Females brood their young in a pouch under their thorax.

Telson

The telson is the posterior-most division of the body of an arthropod. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca may be present. The shape and composition of the telson differs between arthropod groups.

Appendage external body part, or natural prolongation, that protrudes from an organisms body (in vertebrate biology, an example would be a vertebrates limbs); any of the homologous body parts that may extend from a body segment

In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body. An appendage is any of the homologous body parts that may extend from a body segment. These include antennae, mouthparts, gills, walking legs (pereiopods), swimming legs (pleopods), sexual organs (gonopods), and parts of the tail (uropods). Typically, each body segment carries one pair of appendages.

Decapod anatomy The entire structure of a decapod crustacean

The decapod crustacean, such as a crab, lobster, shrimp or prawn, is made up of 20 body segments grouped into two main body parts, the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various groups these may be reduced or missing. They are, from head to tail:

The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa, trochanter, femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus, patella.

<i>Harpaphe haydeniana</i> species of myriapod

Harpaphe haydeniana, commonly known as the yellow-spotted millipede, almond-scented millipede or cyanide millipede, is a species of polydesmidan ("flat-backed") millipede found in the moist forests along the Pacific coast of North America, from Southeast Alaska to California. The dark coloration with contrasting yellow-tipped keels warn of its ability to exude toxic hydrogen cyanide as a defense. Despite the various common names given the species, the coloration pattern, cyanide defense, and associated almond scent occur in other flat-backed millipedes around the world.

Spirobolida order of myriapods

Spirobolida is an order of "round-backed" millipedes containing approximately 500 species in 12 families. Its members are distinguished by the presence of a "pronounced suture that runs "vertically down the front of the head". Most of the species live in the tropics, and many are brightly coloured. Mature males have two pairs of modified legs, the gonopods, consisting of the 8th and 9th leg pair: the posterior gonopods are used in sperm-transfer while the anterior gonopods are fused into a single plate-like structure.

<i>Mammamia</i> genus of myriapods

Mammamia profuga is a species of cave-dwelling millipede in the family Julidae. The only known species of the genus Mammamia, it was described in 2011 from a specimen discovered in a cave in Italy.

<i>Motyxia</i> genus of myriapods

Motyxia is a genus of cyanide-producing millipedes that are endemic to the southern Sierra Nevada, Tehachapi, and Santa Monica mountain ranges of California. Motyxias are blind and produce the poison cyanide, like all members of the Polydesmida. All species have the ability to glow brightly: some of the few known instances of bioluminescence in millipedes.

Polyxenida order of myriapods

Polyxenida is an order of millipedes readily distinguished by a unique body plan consisting of a soft, non-calcified body ornamented with tufts of bristles – traits that have inspired the common names "bristly millipedes" or "pincushion millipedes". There are at least 86 species in four families worldwide, and are the only living members of the subclass Penicillata.

Callipodida order of myriapods

Callipodida is an order of millipedes containing around 130 species, many characterized by crests or ridges.

Orthomorpha coarctata, the long-flange millipede, is a widely introduced species of Polydesmidan millipede of the family Paradoxosomatidae. It is presumed native to Southeast Asia but due to transport by humans occurs in tropical and sub-tropical areas throughout the world, including the Hawaiian Islands, the West Indies, Gulf Coast of North America, and the Galápagos Islands.

Cowiedesmus is an extinct millipede genus known from the middle Silurian of Scotland, and is one of the earliest known land animals. Cowiedesmus was about 4 cm (1.6 in) long and characterized by a greatly enlarged pair of legs on the 8th segment which may have been used in clasping females or functioned as gonopods. Coweiedesmus is distinct enough from other living and fossil millipedes to be placed in its own order, Cowiedesmida. The only known species, C. eroticopodus, was described in 2004.

Archidesmida

The Archidesmida is an extinct order of millipedes known from fossils from the Devonian period of Europe and North America. Archidesmidans have broad flat keels (paranota) extending from their body segments, and a modified pair of legs on the 8th segment that may have been involved in mating, similar to the gonopods of living millipedes which insert sperm into females. Alternately, the modified legs may have been used to grasp onto partners during mating.

<i>Brachycybe</i> genus of myriapods

Brachycybe (Greek for "short head") is a genus of andrognathid millipedes with species in the United States and East Asia. In a rare example of paternal care in invertebrates, males of most species guard the eggs until they hatch.

Juliformia superorder of millipedes

Juliformia is a taxonomic superorder of millipedes containing three living orders: Julida, Spirobolida, and Spirostreptida, and the extinct group Xyloiuloidea known only from fossils. The species possess long cylindrical bodies with sclerites fused into complete rings. Juliform millipedes possess defensive repugnatorial glands on all body segments except the last few, and are the only known millipedes to produce quinones in their defensive secretions. Juliform males have two pairs of gonopods consisting of the modified 8th and 9th pair of legs: in Julida and Spirobolida the posterior gonopods are primarily involved in sperm-transferring, while in Spirostreptida it is the anterior gonopods. Juliformians also lack Tömösváry organs and have a large collum which overhangs the rear of the head.

Ammodesmidae family of myriapods

Ammodesmidae is a family of small millipedes endemic to Africa, containing seven species in two genera. Ammodesmids range from 1.4 to 5.0 mm long with 18 or 19 body segments in both sexes, and are capable of rolling into a tight sphere.

<i>Boreohesperus</i> genus of myriapods

Boreohesperus is a genus of paradoxosomatid millipedes containing six species native to Western Australia. The name refers to the northwestern distribution in Australia, deriving from Boreas, Greek god of the North, and hesperus, Latin for "west".

References

  1. Capinera, John L., ed. (2008). Encyclopedia of Entomology (2nd ed.). Dordrecht: Springer. p. 1633. ISBN   9781402062421.
  2. Nath, Paras (2007). Illustrated Dictionary of Entomology. Pitam Pura, New Delhi: New India Publishing Agency. p. 183. ISBN   9788189422561.
  3. Bauer, Raymond T. (1986). "Phylogenetic Trends in Sperm Transfer and Storage Complexity in Decapod Crustaceans" (PDF). Journal of Crustacean Biology. 6 (3): 313–325. doi:10.2307/1548173.
  4. Sierwald, Petra; Bond, Jason E. (2007). "Current Status of the Myriapod Class Diplopoda (Millipedes): Taxonomic Diversity and Phylogeny". Annual Review of Entomology . 52 (1): 401–420. doi:10.1146/annurev.ento.52.111805.090210. PMID   17163800.
  5. 1 2 Shear, William A. (1999). "Millipeds". American Scientist. 87: 232–240. doi:10.1511/1999.3.232.
  6. Mesibov, Robert. "Gonopods". External Anatomy of Polydesmida. Retrieved 27 October 2013.
  7. Car, Catherine; Harvey, Mark (2013). "A review of the Western Australian keeled millipede genus Boreohesperus (Diplopoda, Polydesmida, Paradoxosomatidae)". ZooKeys. 290: 1–19. doi:10.3897/zookeys.290.5114. PMC   3677291 . PMID   23794855.
  8. 1 2 Drago, Leandro; Fusco, Giuseppe; Garollo, Elena; Minelli, Alessandro (2011). "Structural aspects of leg-to-gonopod metamorphosis in male helminthomorph millipedes (Diplopoda)". Frontiers in Zoology. 8 (1): 19. doi:10.1186/1742-9994-8-19. PMC   3170261 . PMID   21859471.