Abstract

The Zebra Shark, in recent years known as Stegostoma fasciatum (Hermann, 1783), is well known for its dramatic ontogenetic change of color pattern, from striped (“zebra”) juveniles to spotted (“leopard”) adults. Nevertheless, many aspects of the species' biology, ecology, and morphology are still unknown or inadequately described, and its nomenclature is contentious. This study introduces a hitherto undescribed color morph of the Zebra Shark and provides an updated diagnosis and redescription of the species. Firstly, we establish that the Zebra Shark remains a single species based on genetic data from mitochondrial COI and ND4 markers. Secondly, through morphological analyses, we conclude that there are two morphs of the species, the known, zebra striped morph and a new, sandy colored morph. Both morphs were studied morphometrically to expose any ontogenetic changes, such as a decrease in the relative length of the tail with increasing total length (TL). The external coloration pattern clearly differentiates the two morphs, and both morphs can be further divided into three stages based on color pattern and size: juveniles (255–562 mm TL), transitionals (562–1395 mm TL), and adults (>1300 mm TL). The transitional sandy morph is dorsally covered by a swirly pattern of thin, dark brown bands edged with freckle-like brown spots. The adults are a uniform sandy beige, partially covered with brown freckles. A mature male of the zebra morph displayed a yet unknown feature of the claspers: a small, triangular spike extruding from the dorsal terminal of the clasper glands. Finally, we reviewed the nomenclature of the species and suggest that the original name Stegostoma tigrinumForster, 1781 should be used as the senior synonym for the species.

Highlights

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  • Coloration Zebra morph of Stegostoma tigrinum.—The juvenile coloration consists of a dark brown background on the dorsal side and lateral flanks, with 18–25 cream white to yellowish bands stretching from flank to flank, only interrupted by large round or elongated dots of the same color (Fig. 5A)

  • Stegostoma tigrinum has been used at least 21 times from 1903 (Kishinouye and Zashi, 1903) to 2016 (Feldheim et al, 2016)

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Summary

MATERIALS AND METHODS

Molecular work.—Total genomic DNA was extracted from tissue samples (fin clips) from four different sandy color morph specimens (ZMUC P6268, ZMUC P2395374–75, ZMUC P2395470) and two zebra morph specimens (ZMUC P2395372–73). Fifty-two morphometric features were compared and tested for statistically significant differences among juveniles (n 1⁄4 14 specimens, none live), transitionals (n 1⁄4 33, 32 live), and adults (n 1⁄4 5, none live) of the zebra morph; between transitionals (n 1⁄4 4, all live) and adults (n 1⁄4 2, 1 live) of the sandy morph; and between the two morphs. The latter comparison was done with all individuals of the same morph treated as a single group. He used two different common names for the two descriptions; Le requin barbu

Valvular turns
Oral teeth
Dermal denticles
Size and sexual maturity
DISCUSSION
MATERIAL EXAMINED
Findings
LITERATURE CITED
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