Elasmo-Lab, Elasmobranch Research Laboratory, Hamburg, Germany.
Center of Natural History, University of Hamburg, Hamburg, Germany.
PLoS One. 2020 Mar 18;15(3):e0228791. doi: 10.1371/journal.pone.0228791. eCollection 2020.
Recent sampling efforts in Madagascar and Zanzibar, as well as examinations of six-gilled sawsharks in several museum collections provided evidence for a complex of species within Pliotrema warreni Regan. The present manuscript contains a redescription of P. warreni involving the syntypes and additional material, as well as formal descriptions of two new species of Pliotrema Regan. All specimens of both new species were found in the western Indian Ocean. Individuals of the first new species, hereafter referred to as P. kajae sp. nov., were identified originating from Madagascar and the Mascarene Ridge. Specimens of the second new species, hereafter referred to as P. annae sp. nov., were only found off Zanzibar. Pliotrema kajae sp. nov. appears to inhabit upper insular slopes and submarine ridges at depths of 214-320 m, P. annae sp. nov. so far is only known from shallow waters (20-35 m). Both new species differ from P. warreni in a number of characteristics including the known distribution range and fresh coloration. Taxonomical differences include barbels that are situated approximately half way from rostral tip to mouth, with prebarbel length equidistant from barbel origin to symphysis of the upper jaw in P. kajae sp. nov. and P. annae sp. nov. (vs. about two thirds way from rostral tip to mouth, with prebarbel length about twice the distance from barbel origin to symphysis of upper jaw in P. warreni) and rostra that are clearly and slightly constricted between barbel origin and nostrils, respectively (vs. rostrum not constricted). Pliotrema kajae sp. nov. differs from P. annae sp. nov. in a longer snout, more numerous large lateral rostral teeth and upper jaw tooth rows, jaw teeth with (vs. without) sharp basal folds, and coloration, particularly pale to light brown (vs. medium to dark brown) dorsal coloration with (vs. without) two indistinct yellowish stripes. A revised diagnosis of Pliotrema and a key to the species are provided.
马达加斯加和桑给巴尔最近的采样工作，以及对六个鳃锯鲨在几个博物馆藏品的检查，为六鳃锯鲨属中的一个种复合体提供了证据。本手稿包含了对 Pliotrema warreni Regan 的重新描述，涉及模式标本和其他材料，以及两个新种的正式描述。这两个新种的所有标本均发现于西印度洋。第一个新种的个体，以下简称 P. kajae sp. nov.，被确定来源于马达加斯加和马斯克林海脊。第二个新种的标本，以下简称 P. annae sp. nov.，仅在桑给巴尔附近发现。Pliotrema kajae sp. nov. 似乎栖息于 214-320 米深的近海岛屿斜坡和海底山脊，而 P. annae sp. nov. 迄今为止仅在浅水区（20-35 米）发现。这两个新种与 P. warreni 在许多特征上有所不同，包括已知的分布范围和新鲜的颜色。分类学上的差异包括触须位于吻部尖端到口部的大约一半位置，而在 P. kajae sp. nov. 和 P. annae sp. nov. 中，前触须的长度与触须起源到上颌骨联合处相等（而在 P. warreni 中，前触须的长度约为触须起源到上颌骨联合处的三分之二）；以及吻部在触须起源处到鼻孔之间明显且略微收缩（而在 P. warreni 中，吻部没有收缩）。Pliotrema kajae sp. nov. 与 P. annae sp. nov. 的区别在于更长的吻部、更多的大型侧吻部牙齿和上颌牙齿列、具有（而非没有）尖锐的基褶的牙齿，以及颜色，特别是浅到浅棕色（而非中到深棕色）的背部颜色，具有（而非没有）两条不明显的黄色条纹。提供了对 Pliotrema 的修订诊断和物种的关键特征。
