Sternum (arthropod)
Encyclopedia
The sternum is the ventral portion of a segment of an arthropod
thorax
or abdomen
.
In insect
s, the sterna are usually single, large sclerites, and external. However, they can sometimes be divided in two or more, in which case the subunits are called sternites, and may also be modified on the terminal abdominal segments so as to form part of the functional genitalia, in which case they are frequently reduced in size and development, and may become internalized and/or membranous.
Ventrites are externally visible sternites. Usually the first sternite is covered up, so that vertrite numbers do not correspond to sternid numbers.
The term is also used in other arthropod groups such as crustacean
s, arachnid
s and myriapods. Sternites on the pleon (abdomen) of a crustacean may be referred to as pleonsternites. These are the sites of attachment of the pleopods (swimming legs). In spider
s, the sternum is the ventral part of the cephalothorax
.
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
or abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
.
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, the sterna are usually single, large sclerites, and external. However, they can sometimes be divided in two or more, in which case the subunits are called sternites, and may also be modified on the terminal abdominal segments so as to form part of the functional genitalia, in which case they are frequently reduced in size and development, and may become internalized and/or membranous.
Ventrites are externally visible sternites. Usually the first sternite is covered up, so that vertrite numbers do not correspond to sternid numbers.
The term is also used in other arthropod groups such as 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...
s, 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 and myriapods. Sternites on the pleon (abdomen) of a crustacean may be referred to as pleonsternites. These are the sites of attachment of the pleopods (swimming legs). In spider
Spider
Spiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
s, the sternum is the ventral part of the cephalothorax
Cephalothorax
The cephalothorax is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. The word cephalothorax is derived from the Greek words for head and thorax...
.