Pretzmann, 1967 (Crustacea: Brachyura: Pseudothelphusidae)の淡水ガニ属の新種

A new species of freshwater crab genus Pretzmann, 1967 (Crustacea: Brachyura: Pseudothelphusidae) from a naturally isolated orographic forest enclave within the semiarid Caatinga in Ceará, northeastern Brazil.

• Livanio C Santos
• Marcos Tavares
• José R F Silva
• Marcelo Cervini
• Allysson P Pinheiro
• William Santana

抄録

ブラジル北東部セアラー州イプー（Ipú）の標高635～782mの中緯度の森林地帯から、新種の淡水ガニが報告され、図示されている。本種は最初の産卵節の形態から近縁種と区別できる。近位半分は著しく膨らんでおり、遠位に向かって急に下向きに傾斜し、ほぼ直角に近い肩部になる。この種はアマゾンや大西洋流域の低地(<100m)に同所的に生息している。第三紀と第四紀のいくつかの乾燥期に湿った森林が縮小したことで、先祖代々の湿った地域が分断され、先祖代々のカニの個体数が減少した可能性が高い。2つの種は現在、半乾燥のCaatingaによって占められている広大な介在領域によって分離されています。

A new species of freshwater crab, , is described and illustrated from a mid-altitude forested patch in Ipú (Ibiapaba plateau, Ceará, northeastern Brazil), between 635 to 782 m. The new species can be separated from its congeners by the morphology of its first gonopod: proximal half remarkably swollen, sloping abruptly downwards distally to a nearly right-angular shoulder; mesial lobe much smaller than cephalic spine; cephalic lobe moderately developed; auxiliary lobe lip, delimiting field of apical spines, protruded all the way to distal margin of auxiliary lobe. Comparative 16S rDNA sequencing used to infer the phylogenetic placement of n. sp. revealed that it is the sister taxon of , a species which occurs allopatrically in the Amazon and Atlantic basin's lowlands (<100 m). n. sp. and are highly dependent upon humidity and most probably were once part of an ancestral population living in a wide humid territory. Shrinking humid forests during several dry periods of the Tertiary and Quaternary likely have resulted in the fragmentation of the ancestral humid area and hence of the ancestral crab population. evolved and spread in a lowland, humid river basin (Amazon and Atlantic basins), whilst n. sp. evolved isolated on the top of a humid plateau. The two species are now separated by a vast intervening area occupied by the semiarid Caatinga.

©2020 Santos et al.