The pharynx has a powerful muscular wall and contains tiny, calcified, jaw-like structures called "trophi", which are the only fossilizable parts of a rotifer.
en.wikipedia.org The extra-calcified elements are created from small, calcified particles that are found in the fibrous part of the flexor digitorum profundus.
en.wikipedia.org The fin itself is triangular and is composed of long, thin, calcified tubes radiating from the apex.
en.wikipedia.org If the patient has strong cellular immunity, macrophages, epithelial cells and lymphocytes surround the organisms and contain them, and eventually calcify.
en.wikipedia.org Its skeleton is reduced and poorly calcified, the muscle blocks along its sides (myomeres) are weakly developed, and its fins are soft and small.
en.wikipedia.org