Metamerism (biology) in the context of "Segmental ganglia"

Arthropods (/ˈɑːrθrəˌpɒd/ AR-thrə-pod) are invertebrates in the phylum Arthropoda. They possess an exoskeleton with a cuticle made of chitin, often mineralised with calcium carbonate, a body with differentiated (metameric) segments, and paired jointed appendages. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. They form an extremely diverse group of up to ten million species.

Haemolymph is the analogue of blood for most arthropods. An arthropod has an open circulatory system, with a body cavity called a haemocoel through which haemolymph circulates to the interior organs. Like their exteriors, the internal organs of arthropods are generally built of repeated segments. They have ladder-like nervous systems, with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong.

The supraesophageal ganglion (also supraoesophageal ganglion, arthropod brain, or microbrain) generally consists of a set of three fused pairs of ganglia, which constitute the brain in most insect species and in some other closely related arthropods, such as myriapods and crustaceans. It receives and processes information from the first, second, and third metameres. The supraesophageal ganglion lies dorsal to the esophagus and consists of three parts, each a pair of ganglia that may be more or less pronounced, reduced, or fused depending on the genus:

The subesophageal ganglion continues the nervous system and lies ventral to the esophagus. Finally, the segmental ganglia of the ventral nerve cord are found in each body segment as a fused ganglion; they provide the segments with some autonomous control.

Centipedes (from Neo-Latin centi-, "hundred", and Latin pes, pedis, "foot") are predatory arthropods belonging to the class Chilopoda (Ancient Greek χεῖλος, kheilos, "lip", and Neo-Latin suffix -poda, "foot", describing the forcipules) of the subphylum Myriapoda, an arthropod group which includes millipedes and other multi-legged animals. Centipedes are elongated segmented (metameric) animals with one pair of legs per body segment. All centipedes are venomous and can inflict painful stings, injecting their venom through pincer-like appendages known as forcipules or toxicognaths, which are actually modified legs instead of fangs. Despite the name, no species of centipede has exactly 100 legs; the number of pairs of legs is an odd number that ranges from 15 pairs to 191 pairs.

Centipedes are predominantly generalist carnivorous, hunting for a variety of prey items that can be overpowered. They have a wide geographical range, which can be found in terrestrial habitats from tropical rainforests to deserts. Within these habitats, centipedes require a moist microhabitat because they lack the waxy cuticle of insects and arachnids, causing them to rapidly lose water. Accordingly, they avoid direct sunlight by staying under cover or by being active at night.

In biology, a tagma (Greek: τάγμα, pl.: tagmata – τάγματα - body of soldiers; battalion) is a specialized grouping of multiple segments or metameres into a coherently functional morphological unit. Familiar examples are the head, the thorax, and the abdomen of insects. The segments within a tagma may be either fused (such as in the head of an insect) or so jointed as to be independently moveable (such as in the abdomen of most insects).

Usually the term is taken to refer to tagmata in the morphology of members of the phylum Arthropoda, but it applies equally validly in other phyla, such as the Chordata.