Esox lucius, Linnaeus, 1758

Texereau, Megann, Germain, Damien & Meunier, François J., 2018, Comparative histology of caniniform teeth in some predatory ichthyophagous teleosts, Cybium 42 (1), pp. 75-81 : 78

Esox lucius , Lepidopus caudatus , Thyrsites atun and Sphyraena guachancho

The various sections obtained from Esox lucius ( Fig. 1 ), Lepidopus caudatus ( Fig. 2 ), Thyrsites atun ( Fig. 3 ) and in Sphyraena guachancho ( Fig. 4 ) mainly show common features. In these fishes, the dentine includes odontoblastic processes housed in canaliculi. These canaliculi tend to decrease in number from the base to the apical region of the tooth. In addition, they arborize in several branchings and sometimes emit a panache of highly fine processes that establish connections with each other ( Figs 1C , 2C , 3D , 4B, C ). The odontoblastic canaliculi follow a general direction parallel to the axis of the tooth except when they approach the external surface of the tooth where they arrange perpendicularly direction ( Figs 2C , 3D , 4C ). In addition to the odontoblastic canaliculi, a vascular system is also observed in the thickness of the teeth with numerous vascular canals, most of them being anastomosed ( Figs 1C , 2C , 3D , 4B, C ). Such an organization, with odontoblastic canaliculi and vascular canals present, characterizes a specific variety of dentine named osteodentine ( Lison, 1954). It is composed of simple units, the denteones ( Francillon-Vieillot et al., 1990), organized around a vascular canal ( Figs 1B , 2B, C , 3B, C ). They are separated from each other by bands of calcified fibrous tissue composed of collagen fibres.

Examination in polarized light might evidence nicely the spatial organization of these fibres. In Sphyraena guachancho , the observation of a cross section in polarized light revealed their presence in dentine matrix. In fact, these fibres surrounding the vascular canals, are highly birefringent and appear in bright tint. However, in longitudinal section, they do not polarize and appear in dark. These collagen fibres are aligned parallel to each other and are therefore following a trajectory parallel to the direction of vascular canals and to the long axis of the tooth ( Fig. 4B, C ).

The teeth of these four predators do not show dentin folds projecting into the base of the tooth, i.e. plicidentine is absent. The different sections show an enameloid layer around the teeth. This layer thickens gradually toward the apex of the tooth to the point that for some specimens, it forms a real cap of enameloid, the so-called cap acrodine ( Figs 1A , 2B , 3A , 4A ). A thick layer of enameloid is noticed on the cutting edge of the teeth in Thyrsites atun ( Fig. 3B, C ).

Figures

Figure 1. – Esox lucius (Esocidae). A: 3-D reconstruction of the premaxilla (pmx) with a virtual axial section of a caniniform tooth showing vascularized dentine (de) covered with a thin enameloid (en) layer; B: Virtual cross section of the tooth caniniform in A hav- ing many elementary units, denteone organized around the vascular canals; C: Detail of a longitudinal section (MNHN-Histos 2337 in natural transmitted light) showing many odontoblastic canaliculi (arrowhead) and vascular canals (vc). Scale bars:A = 5 mm; B = 2 mm; C = 50 μm.

Figure 2. – Lepidopus caudatus (Trichiuridae). A: 3-D reconstruc- tion of the premaxilla (pmx) with a virtual axial section of a caniniform tooth showing vascularized dentine (de) covered with a thin enameloid layer; B: Virtual cross section of the tooth caniniform in A having many denteones; C: Detail of a cross section (MNHN- Histos 2347 in natural transmitted light) showing the presence of denteones (asterisks) and anastomosed vascular canals (arrowheads). Odontoblastic canaliculi (oc) take an orientation perpendicular to the axis of the tooth as it approaches the outer surface of the tooth. Scale bars:A = 5 mm; B = 2 mm; C = 50 μm.

Figure 3. – Thyrsites atun (Gemplylidae). A: 3-D reconstruction of the premaxilla (pmx) with a virtual axial section of a caniniform tooth showing vascularized dentine (de) covered with a thin enameloid layer and a cap of enameloid (en); B: Virtual cross section of a caniniform tooth showing dentine folds (white arrows) and many denteones at the dentine; C: Cross section (MNHN-Histos 2340 in natural transmitted light) showing the presence of many denteones (arrowheads) and many branches of odontoblastic canaliculi (oc), some of these branches form highly visible plumes (arrows); D: Detail of the cross section in B (MNHN-Histos 2340 in natural transmitted light) showing the presence of denteones (asterisks), many ramified odontoblastic canaliculi (oc) (white arrowheads) and anastomosed vascular canals (vc). Scale bars: A = 5 mm; B, C = 2 mm; D = 20 μm.

Figure 4. – Sphyraena guachancho (Sphyraenidae). A: 3-D reconstruction of the premaxilla (pmx) with a virtual axial section of a canini- form tooth showing vascularized dentine (de) covered with a thin enameloid layer and a cap of enameloid (en); B: Longitudinal section (MNHN-Histos 2332 in polarized light) showing the spatial organization of collagen fibers that follow a trajectory parallel to the direction of the vascular canals and to the main axis of the tooth (black arrowheads); the tooth is covered with a thin enameloid (en) layer; C: Detail of the longitudinal section in B (MNHN-Histos 2332 in polarized light) showing the presence of odontoblastic canaliculi perpendicular to the tooth area (black arrowheads); the tooth is covered with a thin enameloid layer (en). Scale bars:A = 5 mm; B = 10 μm; C = 40 μm.