Apesar do crescente aporte de informações na sistemática das serpentes Neotropicais, impulsionado pelo desenvolvimento de técnicas moleculares, as relações evolutivas intra e intertribais da subfamília Xenodontinae ainda são incipientes, e o posicionamento de gêneros e espécies de várias de suas tribos é desconhecido. A tribo Tachymenini (Dipsadidae, Xenodontinae) abriga sete gêneros e 33 espécies válidas, amplamente distribuídas na América do Sul, e representadas por um complexo histórico taxonômico e uma diversidade subamostrada. O presente projeto visou estudar as relações evolutivas de Tachymenini, de modo a testar as hipóteses de relacionamento entre seus gêneros e espécies em um contexto integrativo, e assim validar mudanças taxonômicas. Todos os táxons válidos de Tachymenini foram examinados, sendo este o trabalho mais abrangente para a tribo. Foram realizadas análises filogenéticas de Máxima Parcimônia, Máxima Verossimilhança e Bayeasiana, a partir da codificação de 70 caracteres morfológicos e do sequenciamento de três genes mitocondriais e três nucleares. As análises filogenéticas recuperaram Tachymenini como monofilética e seus gêneros mais especiosos, Tachymenis, Thamnodynastes e Tomodon, polifiléticos. Dois novos gêneros e quatro novas espécies são propostas, três espécies são sinonimizadas e dois outros gêneros são revalidados, resultando em uma nova classificação com 10 gêneros e 35 espécies para a tribo. Ainda, três complexos de espécies crípticas foram recuperados, o que aumentaria a diversidade de Tachymenini em pelo menos quatro novas espécies. O uso de dados morfológicos e moleculares combinados foi fundamental para o melhor entendimento das relações entre os gêneros da tribo, e para o estabelecimento de seus caracteres diagnósticos. Outros tipos de abordagens, além de complementação de lacunas amostrais, tanto morfológicas quanto moleculares, são necessárias em estudos sistemáticos futuros de Tachymenini e outros grupos de xenodontíneos / In spite of the incoming flow of information regarding the systematics of Neotropical snakes, largely driven by the innovation of new techniques for molecular data, the evolutionary relations among members of the subfamily Xenodontinae are incipient, and the phylogenetic status of several genera and species are still unknown. The tribe Tachymenini (Dipsadidade, Xenodontinae) is composed by seven genera and 33 species widely distributed throughout South America, and characterized by a complex taxonomic history and a hidden diversity. This project aimed to study the phylogenetic relations of Tachymenini, testing the evolutionary hypotheses of relationships among its genera and species in an integrative approach, and to further validate taxonomic changes. All Tachymenini taxa were analyzed in the most comprehensive study of the tribe. Maximum Parsimony, Maximum Likelihood and Bayesian analysis were performed using 70 morphological characters, three mitochondrial and three nuclear genes. Phylogenetic analysis recovered Tachymenini as monophyletic, and its most specious genera, Tachymenis, Thamnodynastes and Tomodon, as polyphyletic. Two new genera and four new species are proposed, three species are synonymized, and two other genera are resurrected, resulting in a new composition of 10 genera and 35 species for the tribe. Nevertheless, three cryptic species complexes were recovered, which would increase the diversity for Tachymenini in at least four other species. The combined use of morphological and molecular data was fundamental for a better understanding of the genera relationships, and for the establishment of diagnostic characters for the taxa. Other approaches, along with the improvement of morphological and molecular data deficiencies, are necessary in future studies of Tachymenini and other Xenodontinae systematics

Student Number : 9613963J - PhD thesis - School of Animal, Plant and Environmental Sciences - Faculty of Science / Animals living in cold environments show physiological, morphological and behavioural adaptations to low temperatures. The African ice rat, Otomys sloggetti robertsi, which is endemic to the southern African Drakensberg and Maluti mountains above 2000m, is an interesting exception since, unlike most alpine small mammals, it does not hibernate or display torpor and is physiologically poorly adapted to low temperatures. It is a strict herbivore, feeding on a low quality diet. Ice rats do show some morphological (e.g. short tails) and behavioural (e.g. communal huddling; constructing underground burrows) adaptations, but little else is known about their biology, particularly how they maximise energy gain to meet thermoregulatory requirements, especially during cold periods. Since feeding represents the primary method of energy gain in endotherms, I studied aspects of the foraging biology of ice rats, including gut structure, foraging patterns and habitat choice. The gut structure of O. s. robertsi is well adapted for a high fibre, herbivorous diet and shows broad similarities with those of its mesic- and arid-occurring relatives. However, O. s. robertsi showed increased dimensions of several foregut organs which may be adaptations for increased energy uptake and/or poor diet quality in alpine environments. Furthermore, females had a larger stomach as well as a longer caecum, small and large intestine in summer than in winter but the gut of males was unaffected; such sexual asymmetry may be related to increased energy requirements of females during pregnancy and lactation. Environmental influences on the aboveground behaviour of O. s. robertsi were investigated by recording the duration of behaviours as well as sequential transitions among behaviours. Ice rats spent most of their day foraging and basking, and much time was spent in their underground burrows. Seasonal comparisons revealed that ice rats spent significantly more time acquiring energy through foraging in winter, whereas they remained below ground for longer periods of time during the middle of the day in summer to escape extreme heat and solar radiation. To understand how low temperatures and predation influenced foraging patterns, the behaviour of ice rats was studied in summer and winter in a population where predators were minimal and in another population which experienced higher levels of predation. Ice rats are central place foragers that travel short distances to forage and display significant seasonal variation in their foraging patterns. In the absence of predation risk, ice rats generally returned to a central place with forage, even though returning to a burrow after foraging in winter was energetically costly. However, these costs must be weighed against the benefits of avoiding exposure to low temperatures by feeding under cover as well as the loss of collected food and possible injury associated with aggressive interactions with conspecifics. Under moderate predation pressure in both seasons, ice rats followed a central place foraging strategy to minimise predation risk, always returning to a burrow entrance with forage collected elsewhere. However, when no perceivable threat was observed, ice rats displayed ‘optimal’ foraging patterns in summer similar to those recorded in the absence of predation pressure and only returned to a burrow with forage as distance from that burrow increased, suggesting that ice rats display facultative foraging decision making in response to multiple environmental cues. The distribution of occupied ice rat burrows was correlated against several environmental factors to determine microhabitat requirements. Ice rat burrows were situated in close proximity to herbaceous and wetland plants, but away from woody vegetation, suggesting that habitat choice is related to the presence of food plants and reduction of shade, facilitating short travel distances during foraging as well as promoting basking. Despite the physiological shortcomings of ice rats, the gut structure, foraging behaviour, and habitat choice of the taxon are adapted for life in cold alpine habitats, most likely by maximising energy intake. Similarities in foraging behaviour and habitat use between O. s. robertsi with its closely-related arid-occurring relative Parotomys spp. suggest phylogenetic influences, but it is possibly more a reflection of similar phenotypic responses to the extreme habitats inhabited by these otomyines.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2014. / Anteosaurs (Therapsida: Dinocephalia: Anteosauria) were the dominant terrestrial predators during the late Middle Permian period and became extinct at the close of the Tapinocephalus Assemblage Zone. Only two genera of anteosaurs, Australosyodon and Anteosaurus, are recognised from the Karoo rocks of South Africa. A newly discovered small anteosaurid skull from the Abrahamskraal Formation is fully described. Because of its relatively large orbits, the unfused nature of its sutures, and the lack of replacement teeth in the dental alveoli, the specimen is considered to be a juvenile Anteosaurus magnificus. A full computer-aided 3-D reconstruction of the skull enabled cranial measurements to be taken for an allometric analysis which included twenty-three measurements and eleven specimens. Positive allometry was found for four of the measurements suggesting fast growing in the temporal region, and a significant difference in the development of the postorbital bar and suborbital bar between juveniles and adults. Phylogenetic research shows that the Russian anteosaurids to be forerunners to Anteosaurus, and because the juvenile Anteosaurus (BP/1/7074) manifests many features of both Syodon and Titanophoneus, it is suggested that ontogenetic growth of Anteosaurus follows Haeckel’s Law.

Dans le cadre du développement de nouvelles technologies pour la protection environnementale, et tout particulièrement pour la dépollution de l’eau ou de l’air, le présent travail de thèse porte sur la mise en œuvre de matériaux semiconducteurs à morphologies contrôlées, susceptibles d’activités photocatalytiques permettant la dégradation ou la transformation de molécules en milieux aqueux. Plusieurs types de synthèses conduisant à des morphologies diversifiées ont été mises en œuvre. Chaque matériau a été caractérisé par diffraction de rayons X, microscopies électroniques à balayage et en transmission, et parspectroscopie Raman. La réflectance diffuse a été utilisée pour déterminer les énergies de bandes interdites des matériaux. Compte tenu des propriétés déjà connues pour les tungstates de type MWO4, notre choix s’est orienté vers trois matériaux : le trioxyde WO3, le tungstate SrWO4 et un nouveau tungstate NaCe(WO4)2 ou Na0,5Ce0,5WO4. L’oxyde WO3 a été choisi comme matériau de référence. Pour ce matériau, deux types de morphologies ont été obtenues : des nanoplaquettes et des nanosphères. Le tungstate SrWO4 de structure scheelite a été synthétisé sous deux formes microstructurales : des sphères et des navettes. Un nouveau matériau a été synthétisé et caractérisé : le tungstate double Na0,5Ce0,5WO4 de structure scheelite. Pour cette nouvelle phase, trois morphologies 3D hiérarchisées ont été élaborées en utilisant la méthode hydrothermale en présence d’EDTA. Pour chaque morphologie observée, un mécanisme de germination-croissance est proposé. Les performances photocatalytiques des différentes formes morphologiques ont été évaluées lors de la dégradation de la rhodamine B (RhB) et du bleu de méthylène (BM), sous rayonnements UV et visible. L’efficacité photocatalytique des différentes microstructures a été étudiée en fonction du pH du milieu réactionnel. À partir des résultats obtenus, nous avons pu montrer la forte corrélation entre largeur de bande interdite et réactivité photocatalytique, mais aussi entre morphologies, tailles et propriétés photocatalytiques. Il est apparu que la dégradation reposesur deux mécanismes complémentaires : l’adsorption des molécules due à la porosité des microstructures et à leur morphologie, et la réaction photocatalytique due aux radicaux actifs générés par les paires e-/h+ photogénérées. Ainsi, la RhB se décompose en présence de SrWO4 et WO3 sous UV-C (254 nm) et UV-Vis (365 nm) respectivement. Le bleu de méthylène se dégrade en présence de NaCe(WO4)2 sous rayonnement solaire UV-Vis. / In the framework of the development of new technologies for environmental protection, andmore specially for the depollution of water or air, this work deals with the implementation ofsemiconductor materials with controlled morphologies, likely photocatalytic activities andtheir enabling the degradation or transformation of organic molecules in aqueous media.Several types of syntheses leading to diversified morphologies have been implemented. Eachmaterial was characterized by X-ray diffraction, scanning and transmission electronmicroscopies, and Raman spectroscopy. Diffuse reflectance was used to determine the bandgap of the materials. Given the properties already known for MWO4 tungstates, we chosethree materials: WO3 trioxide, SrWO4 tungstate and a new tungstate NaCe(WO4)2 orNa0.5Ce0.5WO4. The oxide WO3 was chosen as the reference material. For this material, twotypes of morphologies were obtained: nanoplates and nanospheres. The tungstate SrWO4 withscheelite structure was synthesized in two microstructural forms: spindles and spheres. A newmaterial was synthesized and characterized: double tungstate of Na0.5Ce0.5WO4 with scheelitestructure. For this new phase, three hierarchical 3D morphologies were developed using thehydrothermal method in the presence of EDTA. For each observed morphology, agermination-growth mechanism is proposed. The photocatalytic performances of the differentmorphological forms were evaluated during the degradation of rhodamine B (RhB) andmethylene blue (MB), under UV and visible radiation. The photocatalytic efficiency of thedifferent microstructures was studied as a function of the pH of the reaction medium. Fromthe results obtained, we have been able to show the strong correlation between band gap andphotocatalytic reactivity, but also between morphologies, sizes and photocatalytic properties.It has been shown that the degradation is based on two complementary mechanisms: theadsorption of molecules due to the porosity of the microstructures and their morphology, andthe photocatalytic reaction due to the active radicals generated by the photogenerated e-/ h+pairs. Thus, RhB decomposes in the presence of SrWO4 and WO3 under UV-C (254 nm) andUV-Vis (365 nm) respectively. Methylene blue degrades in the presence of NaCe(WO4)2under UV-Vis solar radiation.

Gorgonocephalus eucnemis, Ophiothrix suensonii and Ophiothrix spiculata are aerobic Echinoderms. Previous observations on the anatomy of these two genera state five pairs of radial shields and genital plates are responsible for regulating the position of the roof of the body disc and the flushing of water in and out of the bursae. Rates of bursal ventilation increase by an average 60-64% when the ophiuroid is exposed to an increase in food or a decrease in dissolved oxygen in Gorgonocephalus. When exposed to hypoxic oxygen concentrations O. suensonii and O. spiculata increased bursal-ventilation rates by (means of) 35% and 28%. Measurements of DO from inside and outside the bursae show that DO is being absorbed during bursal-ventilations. These findings suggest bursal ventilation is a means of respiration and increased rates of bursal-ventilation may help meet increased oxygen demands during feeding and some periods of hypoxia. This dissertation includes unpublished, co-authored material.

The anterior cingulate cortex (ACC) can influence emotional and motivational states in primates by its dense connections with many neocortical and subcortical regions. Pyramidal neurons serve as the basic building blocks of these neocortical circuits, which have been extensively studied in other brain regions, but their morphological and electrophysiological properties in the primate ACC are not well understood. In this study, we used whole-cell patch clamp and high-resolution laser scanning confocal microscopy to reveal the general electrophysiological properties and detailed morphological features of layer 2 and 3 pyramidal neurons in ACC (area 24/32) of the rhesus monkey. Neurons from both layers had similar passive membrane properties and action potential properties. Morphologically, dendrites of layer 3 ACC neurons were more complex than those of layer 2 neurons, by having dendrites with longer total dendritic lengths, more branch points and dendritic segments, spanning larger convex hull volumes. This difference in total dendritic morphology was mainly due to the apical dendrites. In contrast, the basal dendrites displayed mostly similar features between the two groups of neurons. However, while apical dendrites extend to the same layer (layer 1), the basal dendrites of layer 3 extended into deeper layers than layer 2 because of the difference in soma-pia distance. Thus, basal dendrites of the two groups of neurons receive different laminar inputs. Analysis of spines showed that more spines were found in neurons of layer 3 apical dendritic arbors than layer 2 neurons. However, the apical spine densities were similar between neurons in the two layers. Thus, while higher spine number suggests that layer 3 neurons receive more excitatory input than layer 2 neurons, the similar spine density suggests similar spatial and temporal summation of these inputs. The combined effects of increased number of excitatory input and higher dendritic complexity in layer 3 than in layer 2 ACC neurons suggest the additional information received by layer 3 neurons, especially in the apical dendrites, might undergo more complex integration.

Les travaux portant sur l'amalgamation lexicale (ou « mot-valisation » pour reprendre une formulation de Fradin & al., 2009 : 36), ont permis d'établir une description assez précise du phénomène, tout en rendant compte des différentes structures morpho-phonologiques que peuvent revêtir les amalgames. Pourtant, aucune tentative d'élaboration de règles d'amalgamation n'a jusqu'alors été proposée en français. Cette thèse vise à évaluer la possibilité et les moyens d'élaborer un modèle de description systématique du procédé permettant la formulation de règles de construction des amalgames lexicaux en français. Cette approche recourt à la Théorie de l'optimalité pour envisager la production d'une grammaire des amalgames, à l'image des études précédemment conduites par Bat-El (1996), Piñeros (2004) ou Hong (2005). / Studies on lexical blending in French, have established a fairly accurate description of the phenomenon, while reflecting the different morpho-phonological structures of blends. However, no attempt at developing rules of blending has been proposed previously in French. This thesis aims at assessing the opportunity and the means to develop a model of systematic description of the process, in order to formulate rules for constructing lexical blends in French. Our approach uses Optimality Theory, among other theories, to identify a prototype of lexical blend and to consider the making of a grammar of blending, like previous studies conducted by Bat-El (1996), Piñeros (2004) and Hong (2005) have.

Nos travaux de thèse ont pour but d’étudier la manifestation de la néologie dans un dictionnaire de langue française. Nous avons choisi de travailler à partir de la version électronique du "Nouveau Petit Robert" parce qu’il incarne un dictionnaire de référence. Nous avons étudié les mots nouveaux attestés entre 1990 et 2012 dans le "Nouveau Petit Robert Électronique" 2012. Nous avons sélectionné une période d’attestation récente, nous voulions observer l’influence qu’avait eu le développement des nouvelles technologies sur le lexique. Le corpus dont nous disposons se compose de 477 mots nouveaux attestés entre 1990 et 2012. Dans notre travail, nous avons mis en évidence les modes de formations de ces mots nouveaux ainsi que les domaines d’expérience auxquels ils sont rattachés. Nous avons aussi consacré une partie à la lexicographie où nous avons mis en lumière les particularités lexicographiques du "Nouveau Petit Robert Électronique" 2012 en comparant quelques extraits des mots du corpus avec deux autres dictionnaires : "Le Petit Larousse Illustré" 2016 et le "Wiktionnaire". Les modes de formation les plus performants des mots du corpus sont ceux relevant de la matrice interne avec un total de 266 mots et ceux relevant de la matrice externe qui regroupe 186 mots. Les mots du corpus appartenant à la matrice interne sont les plus nombreux, cela montre que le lexique se renouvelle par lui-même. Nous avons observé qu’il y avait un déclin des sciences humaines au profit de sciences techniques. / The purpose of this PhD thesis is to study how neology manifests itself in a french language dictionary. I have chosen to work on the electronic version of the "Nouveau Petit Robert", since it is the epitome of a reference dictionary. I studied the new attested words that were added between 1990 and 2012 in the "Nouveau Petit Robert Électronique" 2012. This fairly recent attestation period was chosen in order to observe the influence of new technologies on the lexicon.To build up our corpus it was necessary to enter the period between 1990 and 2012 as a search criteria. In doing so, the corpus of this study is now composed of 477 new attested words added between 1990 and 2012.This work intends to bring out the formation modes of these new words as well as the experience areas to which they are linked. A portion of this study was also dedicated to lexicography. In this section the lexicographical particularities of the "Nouveau Petit Robert Électronique" 2012 are highlighted by comparing a few words extracted from its corpus with the same words in two other dictionaries : "Le Petit Larousse Illustré" 2016 and the "Wiktionnaire".The most efficient formation modes for the corpus’ words are those pertaining to the internal matrix with a total of 266 words, as well as those pertaining to the external matrix with a total of 186 words.The corpus’words belonging to the internal matrix are the most numerous, and it indicates that the lexicon renews itself on its own.There is a distinct decline of the social sciences in favor of technical sciences to be observed.

A seção Diabroticites Chapuis, 1875 (Chrysomelidae, Galerucinae, Luperini, Diabroticina), com 826 espécies descritas em 17 gêneros, registrada apenas para o continente americano, é uma das maiores assembleias taxonômicas de crisomelídeos. Composta essencialmente por espécies originalmente descritas no gênero Diabrotica Chevrolat, 1837 antes de 1947, é caracterizada pelas garras tarsais bífidas e machos com tíbias mesotorácicas simples, sem projeções. Os mais de 150 anos de história taxonômica da seção foram suportados primariamente por descrições morfológicas superficiais, baseadas em poucos exemplares (geralmente espécimes únicos) e a um número restrito de caracteres, relacionados apenas aos machos. Nunca houve uma revisão do grupo como um todo para investigar a posição sistemática dos Diabroticites como objetivo primário e ampliar o número de caracteres analisados nos dois sexos. O presente trabalho apresenta um estudo morfológico detalhado de vários representantes de Diabroticites visando testar a monofilia da seção, bem como elucidar o posicionamento filogenético dos gêneros que a compõem. Todos os gêneros e a maioria dos agrupamentos infragenéricos da seção foram amostrados no grupo-interno com, ao menos um terminal, num total de 49 terminais. O grupo-externo, incluiu sete terminais, representantes de Cerotomites (Luperini, Diabroticina), Phyllobroticites (Luperini, Luperina), Exosomites (Luperini, Luperina), além de uma espécie de Coelomerites (Galerucini), considerada a raiz. Uma análise de sensibilidade foi realizada, com buscas heurísticas com pesos iguais e pesagem diferencial. O resultado da análise demonstrou que a seção como definida, não forma um grupo monofilético, sendo necessária a inclusão de um ou mais terminais do grupo-externo para recuperar a sua monofilia. Os gêneros que incluíram mais de um terminal, em sua maioria não foram recuperados como clados e os caracteres diagnósticos tradicionalmente utilizados (incluindo diversos caracteres sexuais secundários), em grande parte não corresponderam a sinapomorfias. A única exceção foi Gynandrobrotica, encontrado como um subgrupo de Cerotoma. Caracteres relativos à genitália, utilizados pela primeira vez na elaboração de uma hipótese evolutiva para Diabroticites, tiveram valor significativo na definição das linhagens internas / Diabroticites Chapuis, 1875 (Chrysomelidae, Galerucinae, Luperini, Diabroticina) is one of the largest assemblies of chrysomelids, currently with 826 species in 17 genera, restricted to the American continent. It comprises essentially the species described in genus Diabrotica prior to 1947, characterized by the presence of bifid tarsal claws and males with simple mesothoracic tibiae. Despite having over 150 years of taxonomic history, the species in this group are mostly supported by superficial morphological treatment, frequently based in single specimens, and often relying on male characteristics. There is no general revisionary study for the section to this date, and the systematic position of Diabroticites has never been investigated as a primary objective. A cladistic analysis for the section is hereby presented, based on a detailed morphological study for several diabroticites, in order to test the group\'s monophyly and investigate the phylogenetic position of the genera that are comprised in it. All genera and most infrageneric groups were sampled in the ingroup with at least one terminal (in a total of 49 terminals). The outgroup comprises seven terminals representing section Cerotomites (Luperini, Diabroticina), Phyllobroticites (Luperini, Luperina), and Exosomites (Luperini, Luperina), plus one species of Coelomerites (Galerucini), regarded as the root. The sensitivity analysis included heuristic searches carried with equal and differential weighting. The results indicate that section Diabroticites as currently defined is not monophyletic. Its natural group status can be recovered with the addition of one or more members of the outgroup. Genera that included more than one terminal were, as a rule, not supported as clades, and the traditional diagnostic characters (along with secondary sexual characteristics) for the most part did not correspond to synapomorphies. The sole exception was Gynandrobrotica, found as a subgroup of Cerotoma. Genital characters, used for the first time to support an evolutionary hypothesis for section Diabroticites, were found to have significant value in the definition of internal lineages

O gênero Ischnoplax nunca foi alvo de revisões e é atualmente incluso em uma família com posição taxonômica incerta. O gênero é composto por três espécies distribuídas da Florida (EUA) até Rio Grande do Sul (Brasil), em que uma delas, Ischnoplax incurvata, tem sido alvo de discussão com relação a sua sinonimização como Ischnoplax pectinata. Frente a isso, o presente estudo pretendeu revisar taxonomicamente o gênero Ischnoplax tendo como base o uso das morfologias externa e interna para a composição de um cenário comparativo. Para a revisão do gênero Ischnoplax foram observadas quase todas as espécies tipo. Foram estudados 2.220 espécimes, sendo destes 430 em diferentes estágios de desenvolvimento. Das três espécies atualmente reconhecidas como válidas, I. incurvata e I. edwini são sinônimos da espécie tipo do gênero, I. pectinata, assim como, Lepidochitona montoucheti, Ischnochiton aidae, Ischnochiton lopesi e Callistochiton laticostatus foram igualmente sinonimizadas. Uma espécie nova foi identificada e sua descrição é indicada. Dentre todos os aspectos estudados, a coloração, escultura das valvas, revestimento do cinturão, morfologia das valvas em especial da anal, o número de filamentos branquiais, o estudo da morfologia através da anatomia e o dente radular lateral maior foram fundamentais para a organização taxonômica do gênero. Complementar aos estudos destinados à revisão taxonômica, foram aplicadas técnicas de analise comparativa da morfologia através da dissecção das diferentes espécies. Assim como a taxonomia, a biogeografia do gênero foi revisada e uma reformulação do conhecimento atual, assim como, uma nova ocorrência do grupo para o Uruguai é citada. As diferenças e semelhanças da morfologia observadas em quase todas as estruturas foram suficientes para auxiliar a organização do gênero, assim como a indicação de novos sinônimos e o comportamento das diferentes estruturas nos diferentes estágios de desenvolvimento. / The taxonomy of the genus Ischnoplax has never been revised and is included in a family of uncertain taxonomic position. It is currently composed of three species distributed from Florida (USA) to Rio Grande do Sul (Brazil) of which the synonymization of Ischnoplax incurvata with Ischnoplax pectinata has been widely discussed. The aim of the present study is to undertake a thorough taxonomic review of the genus Ischnoplax using the external and internal anatomy and create a comparative scenario. This involved the analysis of 2.200 specimens, with 430 at different ontogenetic stages and including almost all type specimens. We recognized three valid species. Ischnoplax incurvata and I. edwini were synonymized with Ischnoplax pectinata, for which Lepidochitona montoucheti, Ischnochiton aidae, Ischnochiton lopesi and Callistochiton laticostatus are also synonyms. A new species was identified and a description is given. Of all the characters studied, the color, sculpture of the valves, structures of the girdle, morphology of the valves (especially the tail valve), number of gill filaments, anatomy and the major lateral radular teeth were fundamental for to the taxonomic organization of the genus. Complementary to the taxonomic study we also undertook a comparative analysis of the morphology by means of dissections of different species. The geographical distribution of the genus was also revised and an up-to-date summary of the current knowledge along with a new occurrence from Uruguay are given. The differences and similarities of morphology observed in almost all structures were sufficient to aid in the taxonomic organization of the genus as well as to determine synonyms and the differences between structures at several stages of development.