A tergum (Latin for "the back"; plural terga, associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the base and posterior edge is called the apex or margin. A given tergum may be divided into hardened plates or sclerites commonly referred to as tergites.:20 For a detailed explanation of the terminology, see Kinorhynchs have tergal and sternal plates too, though seemingly not homologous with those of arthropods.
So, for example, in a thoracic segment, the tergum may be divided into an anterior notum and a posterior scutellum. Lateral extensions of a tergite are known as paranota (Greek for "alongside the back") or carinae (Latin for "keel"), exemplified by the flat-backed millipedes of the order Polydesmida.
In crustaceans, the tergum is known as a pleuron when it overhangs the insertion of the limb on each side as a free plate.
In contrast to the tergum, the ventral portion of a segment is called the sternum.
^Sørensen, M. V. et al. Phylogeny of Kinorhyncha based on morphology and two molecular loci. PLoS One 10, 1–33 (2015).
McCafferty, W.Patrick (1983). Aquatic entomology: the fishermen's and ecologists' illustrated guide to insects and their relatives. Jones & Bartlett Publishers, ISBN
0867200170, ISBN 978-0-86720-017-1. Accessed here through Google Books on 08 Jan 2010.
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