Redescription and distributional range extension of a poorly known anchovy Stolephorus nelsoni (Actinopterygii: Clupeiformes: Engraulidae)

Abstract

Background. The poorly known anchovy Stolephorus nelsoni Wongratana, 1987 (Engraulidae), previously known only from the type specimens from Australia, is redescribed and its validity confirmed, on the basis of the holotype, paratype, and 15 additional specimens from Indonesia and Australia. Similar to Stolephorus brachycephalus Wongratana, 1983 in sharing the maxilla reaching more or less to the posterior border of opercle, a predorsal-fin scute absent and the preopercle rounded, the specific distinctiveness of S. nelsoni and differences between the two species have remained unclear. This study sought to confirm the validities of the two species and the distributional range of S. nelsoni. Materials and methods. Seventeen and 9 specimens of S. nelsoni and S. brachycephalus, respectively, including the holotype of each, were examined morphologically, counts and proportional measurements following Hata and Motomura (2017). Results. Comparisons of S. nelsoni with S. brachycephalus revealed the former to have 12–14 (mode 13) branchiostegal rays [vs. 10–11 (11)], 15–17 branched anal fin rays [vs. 20–22 (20)] and relatively fewer gill rakers [37–43 (39, 40) on the first gill arch vs. 35–37 (35)]. Stolephorus nelsoni also differed from S. brachycephalus in body depth [21.7%–23.7% (mean 22.6%) of standard length vs. 18.2%–20.3% (19.1%)], anal-fin base length [16.1%–19.3% (17.6%) vs. 21.6%–24.4% (23.2%)], caudal-peduncle length [15.7%–21.7% (18.8%) vs. 12.6%–15.2% (14.1%)] and snout length [4.5%–5.5% (5.1%) vs. 3.6%–4.3% (4.0%)]. Conclusion. The validities of both species were confirmed, Indonesian examples of S. nelsoni being the first known records of the species outside Australian waters.

Keywords

• taxonomy
• validity
• morphology
• distribution
• Stol