In many Opiliones (notably the Laniatores) the five most anterior opisthosomal tergites are fused with the carapace forming the so called dorsal scutum (DS) (Latreille 1804; Simon 1879; Hadži 1942) with a highly variable shape arising from multiple factors, such as differential development of musculature (especially of coxa IV), internal organs and influence of appendages (Loman 1903; Winkler 1957). The different degrees of fusion of the tergites were first studied by Hadži (1942), who proposed a terminology for them. This terminology was adopted and enhanced by Kratochvíl (1958) and Martens (1978). A shield formed by the fusion of the carapace with abdominal tergites I to V is called scutum magnum (Hadži 1942). The shield formed by the fusion of carapace with abdominal tergites I to VII is called scutum complexum (Kratochvíl 1958) and occurs in the males of Heteropachylinae Kury, 1994 (Kury 1994) and Paralolidae Kratochvíl, 1958 (Kratochvíl 1958). Finally, the scutum completum (Hadži 1942) is formed by the complete fusion of the carapace and abdominal scutum, formed by tergites I to VIII, and occurs in the Sandokanidae (Martens 1978). In this paper we focus on the different forms of the scutum magnum.

The genus Eulibitia was described by Roewer including three species from Colombia and Ecuador: Eulibitia maculata Roewer, 1912, E. annulipes Roewer, 1912 and E. sexpunctata Roewer, 1914. Herein, the genus is revisited and only the type species, Eulibitia maculata Roewer, 1912 is maintained from the previous configuration. Eulibitia sexpunctata is transferred to Ambatoiella Mello- Leitão, 1943 and E. annulipes is considered as Cosmetinae incertae sedis. Acromares lateralis Goodnight & Goodnight, 1943 and Paramessa castanea (Sørensen, 1932) are here considered junior subjective synonyms of Messatana scalaris (Sørensen, 1932) and Eulibitia maculata, respectively. Brachylibitia Mello-Leitão, 1941, currently a junior synonym of Platymessa, is regarded as a synonym of Eulibitia. Platymessa Mello-Leitão, 1941, with two species, and the monotypic genera Messatana Strand, 1942 and Paramessa Mello-Leitão, 1933, are synonymized with Eulibitia Roewer, 1912, yielding the following new combinations: Eulibitia ectroxantha (for Brachylibitia ectroxantha Mello-Leitão, 1941), E. h-inscriptum (for Platymessa h-inscripta Mello-Leitão, 1941) and E. scalaris (for Libitia (Messa) scalaris Sørensen, 1932). Eulibitia is re-diagnosed and five new species are described: E. castor sp. nov., E. pollux sp. nov., E. clytemnestra sp. nov., E. leda sp. nov. and E. helena sp. nov. A key to the nine Eulibitia species is presented; the morphology of Eulibitia is compared with that of Libitia, Libitiella and Ambatoiella.

The genus Platymessa was originally described by Mello-Leitão and diagnosed following the Roewerian system. It originally included two species from the Colombian Andes. Subsequently, a third species was described: Platymessa transversalis Roewer, 1963, which is herein transferred to the genus Chusgonobius Roewer, 1952, forming the new combination Chusgonobius transversalis. Herein, an emended diagnosis is given to Platymessa, the type species, Platymessa h-inscriptum Mello-Leitão, 1941, is redescribed and P. nigrolimbata Mello-Leitão, 1941 is considered its junior subjective synonym. Brachylibitia Mello-Leitão, 1941, is herein considered a junior subjective synonym of Platymessa and its type species, Brachylibitia ectroxantha Mello-Leitão, 1941, considered a species inquirenda, forming the new combination Platymessa ectroxantha. Genital morphology of Platymessa h-inscriptum is described and some characters are discussed regarding their importance in cosmetid taxonomy. Novel forms of sexual dimorphism are described in coxa IV.

The generic name Paecilaema C.L. Koch, 1839 is anchored to the nomen dubium Cosmetus u-flavum Perty, 1833, and the fixation of the latter is proposed by designating a neotype. The choice was made on a potential topotype, being a common species in metropolitan Rio de Janeiro city, SE Brazil, which has been described as new five times and is currently best known as Metavononoides bellus (Mello-Leitão, 1932). Cosmetus u-flavum has been originally included in Paecilaema along with Paecilaema limbatum Kollar in C.L. Koch, 1839, the latter here synonymized with the former. Therefore, our choice of this species is adequate in conveying Koch’s original concept of Paecilaema. The most striking diagnostic feature of the species of Paecilaema is the presence of a lyra, a unique shape of blots in layers of shades of white to pale yellow on the dorsal scutum. Other patterns of scutal white blots are hereby defined and named. Paecilaema is here considered most closely related to Metavononoides Roewer, 1928. Comments are made on the diagnostic characters and the terminology of parts of the lyra is expanded with the introduction of new terms. Comments are made on the formation of the generic name Paecilaema. Taxonomic adjustments are made in the closest relatives of Paecilaema u-flavum, and the following nomenclatural acts are proposed: (1) MNRJ 3433 is designated as male neotype of Cosmetus u-flavum, type species of Paecilaema. (2) Proposed new synonymies: Poecilaema soerenseni Henriksen, 1932 = Paecilaemula bella Mello-Leitão, 1932 = Eucynorta brasiliensis Mello-Leitão, 1923 = Paecilaema limbatum Kollar in C.L. Koch, 1839 = Cosmetus u-flavum Perty, 1833. (3) Nine species originally described elsewhere but currently placed in Metavononoides are transferred to Paecilaema, either as new or as restored combinations: Paecilaemula albisecta Mello-Leitão, 1942, Poecilaemula albosigillata Mello-Leitão, 1941, Paecilaema lyra Sørensen, 1932, Metavononoides melanacanthus Ferreira, Pedroso & Kury, 2005, Paecilaema muticum Sørensen, 1932, Paecilaema ornatissimum Mello-Leitão 1942, Poecilaemula peculiare Roewer, 1917, Paecilaemula preciosa Roewer 1928 and Metavononoides renneri Ferreira, Pedroso & Kury, 2007. (4) The following genera, currently in the synonymy of Paecilaema, are all revalidated and given emended diagnoses: Meterginoides Roewer, 1912, Meterginulus Roewer, 1912, Paecilaemella Roewer, 1925, Pararhauculus Roewer, 1933, Soaresella Goodnight & Goodnight 1947. (5) Their respective type species, currently combined under Paecilaema, are transferred back to their revalidated genera: Paecilaema rastelliferum Pickard-Cambridge 1905 to Meterginulus; Meterginus inermis Banks, 1909 to Meterginoides; Pararhauculus lineatus Roewer, 1933 to Pararhauculus; Paecilaemella festae Roewer, 1925 to Paecilaemella and Soaresella gracilis Goodnight & Goodnight, 1947 to Soaresella.

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