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      Comparative morphology and systematics of the cookiecutter sharks, genus Isistius Gill (1864) (Chondrichthyes: Squaliformes: Dalatiidae)

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          Abstract

          The dalatiid genus Isistius Gill (1864) has three valid species currently recognized in the literature: Isistius brasiliensis Quoy & Gaimard (1824), I. plutodus Garrick & Springer (1964), and I. labialis Meng, Zhu & Li (1985). The most common species, I. brasiliensis, has a wide geographic distribution and is found in subtemperate and tropical seas circumglobally. A comparative analysis of specimens from different localities throughout its range, however, had never been undertaken. In the present paper, the morphological variation of this species along its entire distribution has been thoroughly analyzed, corroborating that it represents a single widespread species and that I. labialis is its junior synonym. The other congeneric species, I. plutodus, is known from only a few specimens and is also distributed worldwide. A detailed comparative analysis of available material of I. plutodus was conducted verifying its validity as a single widespread species. The present study analyzed in detail the external morphology (coloration, dentition, dermal denticles), internal morphology (skeleton, musculature), lateral-line canals, and morphometric and meristic characters of species of Isistius in order to better define the genus and its included valid species.

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          Extinction risk and conservation of the world’s sharks and rays

          The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes—sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world’s ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery. DOI: http://dx.doi.org/10.7554/eLife.00590.001
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            Enzyme clearing of alcian blue stained whole small vertebrates for demonstration of cartilage.

            Preparation of small vertebrates cleared after alcian blue staining of cartilage is facilitated by trypsin digestion. Specimens are fixed in formation, washed, skinned, and eviscerated. After staining in a solution of alcian blue in acetic acid-alcohol for 24-48 hours, they are transferred to water through graded alcohols. Excess alcian blue is removed over a period of up to three weeks by changes every 2-3 days of 1% trypsin in approximately one-third-saturated sodium borate. Bony tissues may be stained after this in a solution of alizarin red S in 0.5% KOH. Specimens are bleached if necessary and dehydrated through graded KOH-glycerine mixtures for storage in glycerine. Since alcohol treatment in addition to formalin fixation does not affect results with this method, it should be useful to researchers who want to study the cartilage or cartilaginous skeletons in museum specimens, which are routinely fixed in formalin and stored in alcohol.
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              Phyletic Relationships of Living Sharks and Rays

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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: Funding acquisitionRole: InvestigationRole: MethodologyRole: Project administrationRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Formal analysisRole: Funding acquisitionRole: Project administrationRole: ResourcesRole: SupervisionRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                20 August 2018
                2018
                : 13
                : 8
                : e0201913
                Affiliations
                [1 ] Departamento de Botânica e Zoologia, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil
                [2 ] Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil
                [3 ] American Museum of Natural History, New York, NY, United States of America
                University of Michigan, UNITED STATES
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Author information
                http://orcid.org/0000-0002-9949-5116
                Article
                PONE-D-18-02439
                10.1371/journal.pone.0201913
                6101376
                30125292
                2059857a-e530-421b-906e-fb2eeb507b23
                © 2018 de Figueiredo Petean, R. de Carvalho

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 23 January 2018
                : 24 July 2018
                Page count
                Figures: 54, Tables: 6, Pages: 98
                Funding
                Funded by: funder-id http://dx.doi.org/10.13039/501100001807, Fundação de Amparo à Pesquisa do Estado de São Paulo;
                Award ID: 2012/07668-4
                Award Recipient :
                Funded by: Fundação de Amparo à Pesquisa do Estado de São Paulo (BR)
                Award ID: 2013/09270-0
                Award Recipient :
                Funded by: Conselho Nacional de Desenvolvimento Científico e Tecnológico (BR)
                Award ID: 133880/2012-5
                Award Recipient :
                Funded by: Fundação de Amparo à Pesquisa do Estado de São Paulo (BR)
                Award ID: 2012/05391-5
                Award Recipient :
                Funded by: Fundação de Amparo à Pesquisa do Estado de São Paulo (BR)
                Award ID: 2012/09877-0
                Award Recipient :
                Funded by: Fundação de Amparo à Pesquisa do Estado de São Paulo (BR)
                Award ID: 2012/02349-8
                Award Recipient :
                Funded by: Conselho Nacional de Desenvolvimento Científico e Tecnológico (BR)
                Award ID: 305271/2015-6
                Award Recipient :
                The work was supported by the following: Fundação de Amparo à Pesquisa do Estado de São Paulo (2012/07668-4, 2013/09270-0), FFP, http://www.fapesp.br/en/; Conselho Nacional de Desenvolvimento Cietífico e Tecnológico (133880/2012-5), FFP, http://cnpq.br/; Fundação de Amparo à Pesquisa do Estado de São Paulo (2012/05391-5, 2012/09877-0, 2012/02349-8), MRC, http://www.fapesp.br/en/; Conselho Nacional de Desenvolvimento Científico e Tecnológico (305271/2015-6), MRC, http://cnpq.br/. All funders had important roles in the study design, data collection and analysis, and decision to publish.
                Categories
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                Biology and Life Sciences
                Anatomy
                Biological Tissue
                Connective Tissue
                Cartilage
                Medicine and Health Sciences
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                Biological Tissue
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