Figure 1.
Schematic of the endoskeletal structure of the shark pectoral fin.
The radial number and segment number of this pectoral fin are 13 and 4, respectively (see the text for details). ms, mesopterygium; mt, metapterygium; pt, protopterygium; rd, radial.
Figure 2.
Pectoral fin of the megamouth shark, Megachasma pelagios (OCA-P 20110301).
(A) External morphology of the ventral (left) and dorsal (right) surfaces of the pectoral fin. White boxes represent the sites used for sampling of skin tissues for histological studies. (B) Skeletal structure of the ventral side of the pectoral fin (left) and the dorsal side of the basal cartilages (right). ms, mesopterygium; mt, metapterygium; pt, protopterygium; rd, radial.
Figure 3.
Naked-line networks around the pectoral fin base of the megamouth shark, Megachasma pelagios (OCA-P 20111217).
Table 1.
Pectoral fin measurements of the megamouth shark (OCA-P 20110301; TL = 3.7 m).
Figure 4.
Articulation between the pectoral fin base and the pectoral girdle in the megamouth shark.
(A) Pectoral girdle: lateral view of the right pectoral girdle (left), and close-up view of the articulation surface for the pectoral fin (right). (B) Close-up view of the articulation between the pectoral girdle and the pectoral fin. The pectoral fin base twists approximately 90°. co, coracoid; ms, mesopterygium; mt, metapterygium; pt, protopterygium.
Figure 5.
Schematic diagrams of the articulation between the pectoral girdle and the pectoral fin in most sharks (above) and in the megamouth shark (below).
In the megamouth shark, the girdle and fin articulate to form a hinge joint in which the rotation axis of the joint is nearly vertical to the plane of the fin.
Figure 6.
Pectoral muscles of the megamouth shark.
(A) Lateral view (above) and medial view (below) images. (B) Schematic of the pectoral fin muscle systems. co, coracoid; dpe 1, anterior component of the depressor pectoralis; dpe 2, posterior component of the depressor pectoralis; lpe, levator pectoralis; ms, mesopterygium; mt, metapterygium; pt, protopterygium.
Table 2.
Radial number and radial segment number of lamniform sharks.
Figure 7.
Transverse sections of skin from the dorsal side of the pectoral fin of the megamouth shark.
Locations of skin samples (p1, p2, and p3) are shown in Figure 2A. (A) Cross-section at site p1 with HE staining. (B) Longitudinal section at site p1, with EVG staining. (C) Enlarged view of a cross-section of the exterior dermis at site p1, with EVG staining. (D) Cross-section at site p2 with HE staining. (E) Cross-section at site p3 with EVG staining. (F) Enlarged view of a longitudinal section of collagen fiber bundles from site p1 with EVG staining. Scale bars in A, B, D, and E = 0.2 mm, and in C and F = 0.05 mm; ce, ceratotrichia; cfb, collagen fiber bundles; dd, dermal denticles; ed, epidermis; EF, elastic fibers; mp, melanophores; pl, papillary layer; rle, exterior reticular layer; rli, interior reticular layer; rlm, middle reticular layer; rc, radial cartilage; *, artificial spaces produced by the cutting procedure.
Figure 8.
Transverse sections of skin from the dorsal side of the pectoral fin of Isurus oxyrhinchus and Lamna ditropis.
(A) Semi-longitudinal section at site p1 of I. oxyrhinchus with HE staining. (B) Cross-section at site p3 of I. oxyrhinchus with EVG staining. (C) Enlarged view of a semi-longitudinal section of the exterior dermis at site p1 of I. oxyrhinchus with EVG staining. (D) Cross-section from site p1 of L. ditropis with HE staining. (E) Cross-section at site p2 of L. ditropis with EVG staining. (F) Cross-section at site p3 of L. ditropis with HE staining. Scale bar in C = 0.1 mm, and for all others = 0.2 mm.