Teeth of Plecostomus

     One of the species of the Plecostomus family, Plecostomus cordovae was examined by Theodore H., focusing on the needle-like teeth of pleco fish. The teeth of Plecostomus cordovae are uniform tubes of dentine which contains no enamel, flattened at the tip. The entire set of teeth in each dentary and premaxilla lies in a deep trough in the bone while each tooth attaches by a movable joint just under the overhanging rim of the trough when the tooth is developed completely, as shown in Figure 1.

i., integument of mouth; p.m., premaxilla; t., tooth.

Figure 1: (Left) Ventral aspect of head of Plecostomus cordovae; (Right) Cross-section of premaxilla of Plecostomus cordovae showing development of series of teeth.

     The teeth are piled in vertical series within the jaw, in which the teeth at the bottom being buds in the first stage of development, and those toward the exterior growing progressively more complete and more angular until the last and oldest in the series emerges ready for use. The teeth that break off are replaced by the one below. The dentine is covered by two layers of columnar cells, one outside and another inside the tooth as shown in figure 2. The columnar layer within continues down to the bottom of each papilla and up the adjacent surface of the overlying cap during the earlier stages of the tooth papilla. These layers appear to be identical in the papilla and in the surrounding cap, which suggests that both layers contribute to the deposit of the tooth. It is worth to note that the increase in thickness at the tip is due to the lengthening of individual cells instead of the multiplication of layers.

           

     For more fully developed teeth, the cells within the dentine column become nearly cut off from those outside, as the need to carry materials to the tooth must exist as well as the observed groups of erythrocytes. A capillary passes close to the base of each tooth while sending a loop up into it. Distally the dentine within the tip is transparent, thin and filled with minute canals crossing it as many different angles.

     A series of zones exists along the face of the cavity in which the teeth arise, from bottom to the top. Narrow and nearly straight tip of the teeth formed in the bottom zone; the first segment of the shaft formed in the second zone, preceded by an angle; another segment marked by an opposite bend in the third zone and the final rounded base for articulation with the bone when the tooth is in position for use in the fourth zone. Hence, the growing teeth push those above gradually outward from the bottom of the trough; different effects occur as they come to different levels. Although their nature and factor are unknown, the effects are probably due to a sequence of changes in the secreting tissues. The complete tooth is a lifeless shell as the tissues become less compact within the teeth, eventually shrink away, leaving large gaps and scattered group of cells.

c., columnar cells; cap., capillary; d., dentine; e., erythrocytes

Figure 2: Microscopic section of earliest stages in tooth development of Plecostomus cordovae

Our NEXT POST discussed on how the SUCTION of the Plecostomus' mouth INSPIRED better MEDICAL DEVICES!!!

Reference

http://www.jstor.org/stable/1436721?seq=1#page_scan_tab_contents