View from the ventral side
Sternitis is the abdominal sclerotized part of the arthropod segmental ring. The degree of development of sternites and their structure in different groups of arthropods are different. As a rule, they are slightly smaller (and on segments carrying limbs, often much less) than sclerites of the dorsal part of the segment are tergites , but in some few groups sternites can exceed tergites in size. So, in adult beetles, sternites of the abdomen are noticeably wider than tergites, with the latter plunged into a depression between the edges of the former that rise on the sides. In adults, many insects with complete transformation (for example, dipterans , butterflies , caddis flies ) have their bases close to each other, and the sternites between them are submerged inside the chest and are visible only when opened. In this case, they are called cryptosternites.
Sclerotized formations of the dorsal surface of arthropods are called tergites , and the lateral ones are called pleritis .