Biology Department, Randolph-Macon College, Ashland, VA 23005, USA; Smithsonian Research Associate, National Museum of Natural History, Division of Fishes, Washington, DC 20560, USA.
Zootaxa. 2021 Apr 9;4952(2):zootaxa.4952.2.5. doi: 10.11646/zootaxa.4952.2.5.
Distichodus notospilus was described from the Ogooué River and is considered to occur throughout the Lower Guinea ichthyofaunal province and the western tributaries of the middle and lower Congo River. Recent expeditions in Equatorial Guinea collected D. notospilus specimens in the Mbini River drainage and the Mbia River; a small coastal river that is located between the Ntem and Mbini river drainages. Detailed morphological analyses and multilocus molecular analyses confirm that these two populations are distinct from one another. Topotypic populations of D. notospilus were included in the analyses and demonstrated that populations in the Mbini and Mbia rivers are distinct and these two new species are described herein. Distichodus microps sp. nov. is endemic to the Mbia River drainage and is distinguished from D. notospilus in having more scales along the lateral line (41, rarely 40 versus 37-39, rarely 40), a nearly inferior mouth versus subterminal in D. notospilus, a curved posterolateral margin of the opercle versus straight in D. notospilus, a smaller eye (56.7-80.4 versus 70.1-104.3 % of snout length), and a less prominent elongated spot at the base of the caudal fin. Distichodus mbiniensis sp. nov. is endemic to the upper Mbini River drainage and distinguished from D. notospilus in having more scales along the lateral line (41-42, rarely 40 versus 37-39, rarely 40), a much less prominent elongated dark spot at the base of the caudal fin, and a shorter dorsal fin (21.4-27.2 versus 22.7-34.2% standard length). Distichodus microps is distinguished from D. mbiniensis in having a shallower body (usually six scales from lateral line to the pelvic fin versus seven), fewer anal-fin rays (usually 12 total rays versus 13 or 14), a more inferior mouth, a deeper and longer caudal peduncle, a smaller eye, and differences in several features associated with the head. In addition to the two new species described this study also revealed potential undescribed diversity in the D. notospilus species complex in the Ntem River and Dja River (Congo R. basin) in Cameroon. The biogeography of these fishes in the rivers of Lower Guinea suggests that the Mbini River and smaller coastal rivers are overlooked areas of endemism. Studies of other reported widespread species will likely reveal additional diversity and further elucidate the processes promoting and maintaining freshwater diversity in Central Africa.
多须公鱼被描述于奥果韦河，并被认为存在于下几内亚鱼类区系省和中、下刚果河的西部支流。最近在赤道几内亚的考察队在姆比内河和姆比亚河收集到多须公鱼标本；姆比亚河是一条位于恩特姆河和姆比内河之间的小型沿海河流。详细的形态分析和多基因分子分析证实，这两个种群彼此不同。多须公鱼的模式种群被包括在分析中，并表明姆比内河和姆比亚河的种群是不同的，这两个新物种在这里被描述。多须公鱼微鳃亚种是姆比亚河流域的特有种，与多须公鱼不同，它的侧线上有更多的鳞片（41，很少有 40，而多须公鱼为 37-39，很少有 40），嘴近乎下口而非亚端位，瓣鳃盖的后外侧缘弯曲而非直线，眼睛较小（56.7-80.4 与 70.1-104.3%的吻长），尾鳍基部的拉长暗斑不那么明显。姆比内河多须公鱼是姆比内河上游的特有种，与多须公鱼不同，它的侧线上有更多的鳞片（41-42，很少有 40，而多须公鱼为 37-39，很少有 40），尾鳍基部的拉长暗斑不那么明显，背鳍较短（21.4-27.2 与 22.7-34.2%的标准长）。多须公鱼微鳃亚种与姆比内河多须公鱼的区别在于，前者体较浅（通常从侧线到臀鳍有 6 个鳞片，而后者有 7 个），臀鳍鳍条数较少（通常总鳍条数为 12 条，而后者为 13 或 14 条），口更下位，尾柄更深更长，眼睛更小，以及与头部相关的几个特征存在差异。除了本文描述的两个新种外，本研究还揭示了在喀麦隆的恩特姆河和德贾河（刚果河流域）的多须公鱼物种复合体中存在潜在的未描述的多样性。这些下几内亚河流中的鱼类的生物地理学表明，姆比内河和较小的沿海河流是被忽视的特有种地区。对其他报道的广泛分布物种的研究可能会揭示更多的多样性，并进一步阐明促进和维持中非淡水多样性的过程。
