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| Fredius ibiapaba
Santos, Tavares, Silva, Cervini, Pinheiro & Santana, 2020
DOI: 10.7717/peerj.9370
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Abstract
A new species of freshwater crab, Fredius ibiapaba, 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 Fredius ibiapaba n. sp. revealed that it is the sister taxon of F. reflexifrons, a species which occurs allopatrically in the Amazon and Atlantic basin’s lowlands (<100 m). Fredius ibiapaba n. sp. and F. reflexifrons 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. Fredius reflexifrons evolved and spread in a lowland, humid river basin (Amazon and Atlantic basins), whilst F. ibiapaba 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
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| Figure 3: Fredius ibiapaba n. sp., male cl 36 mm, cw 53 mm (MZUSP 39710). (A–B) Habitus, dorso and ventral views, respectively. (C) Cephalothorax, frontal view. (D–E) Right and left chelipeds in lateral view, respectively. Scales: A–E, 10 mm. |
Family Pseudothelphusidae Ortmann, 1893
Genus Fredius Pretzmann, 1967
Fredius ibiapaba n. sp.
Fredius reflexifrons – Magalhães et al., 2005: 94, fig 1 –Santos et al., 2020: 3.
Diagnosis. G1 robust, proximal half remarkably swollen, sloping abruptly downwards anteriorly to a nearly right-angular shoulder (Figs. 4B, 4C); mesial lobe much smaller than cephalic spine (Figs. 4B, 4C; 5C, 5D; 7A, 7C, 7E); cephalic lobe somewhat broad, rounded apically (Fig. 4A); auxiliary lobe lip, delimiting field of apical spines, protruded all the way to distal margin of auxiliary lobe (Figs. 4A, 4B; 6B; 7D).
Distribution. Currently known from Ipú, Ibiapaba plateau, Ceará, northeastern Brazil, in mid-altitude forests between 665 to 798 m.
Etymology. The specific epithet is a noun in apposition taken from the Tupi language word for plateau, “yby’ababa”, ibiapaba.
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| Figure 1: Sítio Caranguejo, Ipú, Ceará, 729 m high, type locality of Fredius ibiapaba n. sp. (A–E) Mid-altitude, naturally isolated, humid forested patch nested within the vast semiarid Caatinga domain. Note in (E) burrow (arrow) of Fredius ibiapaba n. sp. among the leaf litter. (E–F) Lowland, surrounding semiarid Caatinga forest. (E) View from above from Ipú. (F) Detail of a dry-stream channel. |
Livanio C. Santos, Marcos Tavares, José R.F. Silva, Marcelo Cervini, Allysson P. Pinheiro and William Santana. 2020. A New Species of Freshwater Crab Genus Fredius Pretzmann, 1967 (Crustacea: Brachyura: Pseudothelphusidae) from A Naturally Isolated Orographic Forest Enclave within the Semiarid Caatinga in Ceará, northeastern Brazil. PeerJ. 8:e9370. DOI: 10.7717/peerj.9370
