Stolephorus acinaces, a new anchovy from northern Borneo, and redescription of Stolephorus andhraensis Babu Rao, 1966 (Clupeiformes: Engraulidae)

Stolephorus acinaces sp. nov. is described from 14 specimens from the northern coast of Borneo, Malaysia. The new species is closely related to Stolephorus andhraensis Babu Rao, 1966, which is redescribed, both species having a long upper jaw with the posterior tip beyond the posterior margin of the preopercle, no predorsal scutes, the posterior preopercular margin indented and concave, the posterior tip of the depressed pelvic fin not reaching to a vertical through the dorsal-fin origin, no dark lines on the dorsum, and no black spots below the eye. However, the former is distinguished from S. andhraensis in having higher gill raker counts on the first and second gill arches (14–16 + 21–23 = 36–38 and 9–11 + 18–20 = 27–31, respectively vs. 14–16 + 19–21 = 33–37 and 8–11 + 16–19 = 26–29, respectively in S. andhraensis), a longer caudal peduncle (19.7–21.9% SL vs. 16.9–19.9%), longer pectoral fin (14.3–15.2% SL vs. 12.8–14.4%), and shorter pelvic fin (6.7–7.6% SL vs. 7.4–8.9%). A molecular analysis showed that S. acinaces sp. nov. is the sister group of the clade (S. andhraensis, Stolephorus tamilensis Gangan, Pavan-Kumar, Jahageerdar & Jaiswar, 2020, and S. acinaces sp. nov. has about 7% mean p-distance divergence in the mitochondrial cytochrome oxidase I (COI) gene with each of the two species of this clade.