Hemiodus ternetzi (Myers)

Scharcansky, Alexandre & Lucena, Carlos Alberto S., 2008, Phylogenetic assessment of ultrastructural and histological characters of teeth in the Anostomoidea, Hemiodontidae and Parodontidae (Teleostei: Ostariophysi: Characiformes), Zootaxa 1948 (1), pp. 36-56 : 42-43

Hemiodus ternetzi (Myers) ( Figs. 10 and 11 )

Members of this family lack dentary teeth; consequently, the information below refers to premaxillary teeth.

There is no bone tissue surrounding the base of the teeth. However, we can see a compact bone formation in the posterior region of the premaxilla. The replacement teeth are arranged in six to eight sets (considering both premaxillaries), each corresponding to a functional tooth. Each set is surrounded by adipose and connective tissues. More posterior teeth show an earlier development stage when compared to more anterior teeth, and are aligned in a manner different from that of the functional teeth. Therefore, they show a pre-eruptive rotation. Histologically, the replacement teeth in their final stage show a pattern similar to that of the functional teeth from the exterior inwards: a narrow enamel layer (light tooth area, see Figure 11C ), demineralized due to the histological preparation process, is surrounded by elongated ameloblasts. Next are the dentin layer and the set of odontoblasts, comparatively narrower than the ameloblasts. Starting from the enamel layer we see conspicuous periodontal ligaments already fully developed. Finally, the dental papilla (mesenchymal cells) forms a narrow area.

The functional teeth are connected along the dentin layer to the premaxilla by small periodontal ligaments. The dentin layer is equally narrow all around the teeth. The dental pulp, located after the horizontal line that goes through the bone-tooth connection, is wide and much larger than the tooth base, being bordered in the back by the column of replacement teeth.

Figures

FIGURE 10. Hemiodus ternetzi (Myers, 1997) MCP 22074, 70.88 mm SL – A: Premaxilla and teeth, left side, frontal view. B: Premaxilla tooth, left side, frontal view, apical region detail. C: Premaxilla tooth, left side, frontal view, median region detail. D: Premaxilla tooth, left side, teeth-premaxilla bone attachment detail, frontal view. E: Premaxilla tooth, left side, SEM image showing the crystal apatite arrangement, labiolingual direction.

FIGURE 11. Hemiodus ternetzi (Myers, 1997) MCP 22074, 70.88 mm SL – A: Premaxilla, cross section (10x). B and C: Replacement teeth, 10x and 40x, respectively. In B, arrow points to the apical region. D: Functional teeth (40x); E: Premaxilla, cross section, showing that the tissue supports and fixes the functional teeth; arrows point to the connective tissues surrounding sets of replacement teeth(20x). AM=ameloblasts; DF=functional teeth; DN=dentin; DS=replacement teeth; ES=enamel; LP=periodontal ligament; OD=odontoblasts; PA=dental papilla; PO=pulp; PMX=premaxilla; TC=connective tissue; TE=epithelial tissue; TO=bone tissue.