Abstract
This is the first known report on the skeletal and muscular systems, and the skin histology, of the pectoral fin of the rare planktivorous megamouth shark Megachasma pelagios. The pectoral fin is characterized by three features: 1) a large number of segments in the radial cartilages; 2) highly elastic pectoral fin skin; and 3) a vertically-rotated hinge joint at the pectoral fin base. These features suggest that the pectoral fin of the megamouth shark is remarkably flexible and mobile, and that this flexibility and mobility enhance dynamic lift control, thus allowing for stable swimming at slow speeds. The flexibility and mobility of the megamouth shark pectoral fin contrasts with that of fast-swimming sharks, such as Isurus oxyrhinchus and Lamna ditropis, in which the pectoral fin is stiff and relatively immobile.
Highlights
The first specimen of a megamouth shark (Megachasma pelagios) was captured off Hawaii in 1976
The present study reports on the gross anatomy of the pectoral fin of the megamouth shark, and the histological features of the pectoral fin skin
The sections were stained with hematoxylin and eosin (HE) for general histological examination, or using the Elastica van Gieson (EVG) staining protocol to examine the extracellular matrixes of the fibrillar connective tissue
Summary
The first specimen of a megamouth shark (Megachasma pelagios) was captured off Hawaii in 1976 It was described as a new genus and species in its own family within the order Lamniformes, and it became the third known planktivorous shark, along with basking and whale sharks [1]. The skeletal and muscular systems of pectoral fins have been used for taxonomic investigations in some shark lineages [6,7,8,9]. The anatomy of the pectoral fin has only been examined in 5 out of 15 species of extant lamniforms: Carcharodon carcharias, Carcharias taurus, Lamna nasus, Mitsukurina owstoni, and Pseudocarcharias kamoharai [10,11,12,13,14]
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