Diversity and distribution of Collembola (Arthropoda: Hexapoda) of Brazil

Objectives of this study are to summarize the current state of knowledge of the diversity and distribution of Collembola in Brazil; to identify areas of most importance, interest, and need of additional research; and to enable development of experimental hypotheses for future research on Collembola in this region. The total number of collembolan species currently known from Brazil is 199, distributed among 19 families and 80 genera. The greatest numbers of species have been recorded from the states of Rio de Janeiro and Amazonas (with 69 and 56 species, respectively). Few or no species are known from most Brazilian states. Most of the species for which specific Brazilian environmental habitat information is available (93, 66%) are known only from forest environments. Most of the species (127, 64%) are known only from Brazil (most likely being endemic); 33 species (17%) are known only from Brazil and other neotropical areas; and 39 species (20%) have a distribution beyond the neotropical region. Results of this study indicate that much remains to be learned about the Brazilian collembolan fauna. This is especially true for areas of the northeastern, central-western, and southern regions. Studies to determine the species composition of collembolan communities in specific environments in Brazil are needed. The great diversity of Collembola species in Brazil is largely unknown and there are many opportunities for additional research on these environmentally important organisms in this area. Such additional research on the Collembola in Brazil is also essential for a better understanding of the neotropical (and world) collembolan fauna.     

The basic body plan of arthropods: insights from evolutionary morphology and developmental biology

Phylogenetic, morphological, and developmental data concerning the Arthropoda are reviewed and discussed with the aim of reconstructing the ancestral body plan of the mandibulate arthropods (Myriapoda, Hexapoda, Crustacea). Comparative morphology as well as embryology of malacostracans and hexapods (cell-lineages, patterns of mitotic domains, patterns of en-stripe formation, expression zones of pair-rule, homeotic, and gap-like genes) suggest that (a) the basic boundary subdividing the mandibulate body into the primary embryonic regions, anterior protocephalon and posterior protocorm, runs anteriorly to parasegment PS1 (=within the mandibular segment); (b) protocephalon (pregnathal region) probably is not a unitary body region; (c) maxillary segments are closely related to the postgnathal trunk segments; (d) the “typical” mandibulate head (pregnathal-mandibular-maxillary) is not developed in all Mandibulata and has evolved several times in parallel; and (e) postcephalic tagmosis is much less conserved, and probably more recent, than tagmosis of more anterior areas. The arachnomorphan anterior tagma, the prosoma, is compared with the hypothesized ancestral mandibulate head.     

Embryonic development of a collembolan,Tomocerus cuspidatus Börner, 1909: With special reference to the development and developmental potential of serosa (Hexapoda: Collembola,Tomoceridae)

The embryogenesis of a collembolan, Tomocerus cuspidatus, was examined and described, with special reference to the development of serosa and its developmental potential. As a result of cleavage, which starts with holoblastic cleavage and changes to the superficial type, the blastoderm forms. At the center of the dorsal side of the egg, the primary dorsal organ develops. The mesoderm is segregated beneath the entire blastoderm, excluding the primary dorsal organ. The mesoderm then migrates to the presumptive embryonic area, and the embryonic and extra-embryonic areas differentiate. The area lined with mesoderm is the embryo, and that devoid of it is the serosa. Owing to blastokinesis completion, the extra-embryonic area or the serosa is highly stretched, and the serosal cells are often found to undergo mitosis. The serosa possesses the ability to differentiate into the body wall. It was confirmed, in contrast to the previous understanding, that the serosal cells do not degenerate, but participate in the formation of the body wall or definitive dorsal closure. Integrating this newly obtained information and other embryological evidence, the basal splitting of Hexapoda was phylogenetically discussed and reconstructed, and a phylogeny formulated as “Ellipura (= Protura + Collembola) + Cercophora (= Diplura and Ectognatha)” was proposed.