Sistemática de Pycnogonida : levantamento taxonômico das coleções brasileiras e análise filogenética

Abstract

Class Pycnogonida contains more than 1,300 described species of exclusively marine chelicerates. Few studies are available for the group, particularly from tropical regions. In Brazil the study of Pycnogonida is concentrated between the decades of 1940 to 1970, with 38 new species having been described. Infortunately, records to most of the material on which these descriptions are based has not been found. The material may be lost or hidden among non-catalogued material in several Brazilian institutions. As a result of our search of the type-material, Chapter 1 provides information on Brazilian collections containing Pycnogonida. We describe these collections, and redescribe those few types that have been found. Twenty-seven institutions were contacted, seven of which made material available. In all, 1,800 specimens were analised, identified into 49 nominal species and two new species. The types of Pycnogonum gibberum and Anoplodactylus arescus were located. Neotypes of Achelia sawayai, Tanystylum isabellae and Ascorhynchus corderoi were designated, including new records for Brazil and Uruguay. With the data investigated it has been possible to map the representativity of the national collections, and to define priority areas in need of sampling, such as the Northern coast of Brazil. Such planning would enhance the importance of biological collections as sources of information for biodiversity studies. Presently 12 families and 81 genera of Pycnogonida are accepted. Relationships proposed on the base of morphology and molecules remain incongruent. Such incongruence may be the result of the low representativity of the studied groups. Only 30% of the genera have been analised phylogenetically. Furthermore, most species have been collected only once, and information on type material is largely lacking. Considering this panorama, Chapter 2 presents a qualitative/quantitative analysis of the class Pycnogonida on the basis of morphological information. The monophyly of presently accepted families is tested, and relationships among the genera are provided. For the quantitative analysis information was processed for 1,179 species (86.27% of the species presently considered valid), which are allocated to 80 genera. These species were analysed in the form of pictoric plates. For the quantitative analysis a matrix with 145 terminals and 112 characters was constructed and compared mutually and with selected outgroups. Only three families remained monophyletic in the quantitative analysis. Soma patterns of relationships were repeated in more than one analysis, mainly among the families Nymphonidae and Callipallenidae, Pycnogonidae, Rhynchothoracidae and Austrodecidae, and Ammotheidae, Pallenopsidae, Phoxichilidiidae and Endeidae. Several independent events of evolutionary loss of characters were observed, which produced high levels of homoplsy for the group. The obtained results demonstrate the importance of including broad representations of Pycnogonida in the analyses. Insights into the evolution of the group are thus obtained, and genera of uncertain position have been included herein for the first time. The analyses of pictorical plates is a viable tool for phylogenetic analyses. These plates summarizing morphological information provide access to all available published information, including information on rare groups. They also permit the production of more inclusive analyses. From pictorical plates it is possible to compare in detail the different character states appearing in the group. Hypothesis on character transformations are thus formulated, and character codings can be checked and continuously recoded as a function of new understandings on character evolution. Producing a character matrix is not a trivial process and requires time and patience for the obtention of better results.