Gonopore
Encyclopedia
A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrate
s. Hexapods
, including insect
s have a single common gonopore, except mayflies
, which have a pair of gonopores. More specifically, in the unmodified female it is the opening of the common oviduct
, and in the male, it is the opening of the ejaculatory duct
.
The position of the gonopore varies considerably between groups, but is generally constant within groups, allowing its position to be used as a "segmental marker". In Malacostraca
, it is on the sixth thoracic segment; in Symphyla
it is on the fourth trunk segment; in arachnid
s, it is on the second segment of the opisthosoma
. In insect
s and centipede
s, the gonopores are close to the animal's tail, while in millipede
s, they are on the head. The positions of the male and female gonopores, either on the base of the leg or on the animal's sternum, is important in the systematics
of crab
s.
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. Hexapods
Hexapoda
The subphylum Hexapoda constitutes the largest grouping of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura . The Collembola are very abundant in terrestrial environments...
, including insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s have a single common gonopore, except mayflies
Mayfly
Mayflies are insects which belong to the Order Ephemeroptera . They have been placed into an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies...
, which have a pair of gonopores. More specifically, in the unmodified female it is the opening of the common oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...
, and in the male, it is the opening of the ejaculatory duct
Ejaculatory duct
-Anatomy:The ejaculatory ducts are paired structures in male anatomy. Each ejaculatory duct is formed by the union of the vas deferens with the duct of the seminal vesicle. They pass through the prostate, and open into the urethra at the Colliculus seminalis...
.
The position of the gonopore varies considerably between groups, but is generally constant within groups, allowing its position to be used as a "segmental marker". In Malacostraca
Malacostraca
Malacostraca is the largest of the six classes of crustaceans, containing over 25,000 extant species, divided among 16 orders. Its members display a greater diversity of body forms than any other class of animals, and include crabs, lobsters, shrimp, krill, woodlice, scuds , mantis shrimp and many...
, it is on the sixth thoracic segment; in Symphyla
Symphyla
Symphylans, also known as garden centipedes or glasshouse symphylans, are soil-dwelling arthropods of the class Symphyla in the subphylum Myriapoda. Symphylans resemble centipedes, but are smaller and translucent. They can move rapidly through the pores between soil particles, and are typically...
it is on the fourth trunk segment; in arachnid
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...
s, it is on the second segment of the opisthosoma
Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma . It is a distinctive feature of the subphylum Chelicerata...
. In insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s and centipede
Centipede
Centipedes are arthropods belonging to the class Chilopoda of the subphylum Myriapoda. They are elongated metameric animals with one pair of legs per body segment. Despite the name, centipedes can have a varying number of legs from under 20 to over 300. Centipedes have an odd number of pairs of...
s, the gonopores are close to the animal's tail, while in millipede
Millipede
Millipedes are arthropods that have two pairs of legs per segment . Each segment that has two pairs of legs is a result of two single segments fused together as one...
s, they are on the head. The positions of the male and female gonopores, either on the base of the leg or on the animal's sternum, is important in the systematics
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
of crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s.