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South Brisbane, Australia

Brenneis G.,Humboldt University of Berlin | Arango C.P.,Biodiversity Program | Scholtz G.,Humboldt University of Berlin
Development Genes and Evolution | Year: 2011

Embryonic development of Pycnogonida (sea spiders) is poorly understood in comparison to other euarthropod lineages with well-established model organisms. However, given that pycnogonids potentially represent the sister group to chelicerates or even to all other euarthropods, their development might yield important data for the reconstruction of arthropod evolution. Using scanning electron microscopy, fluorescent nucleic staining and immunohistochemistry, the general course of embryonic morphogenesis in Pseudopallene sp. (Callipallenidae), a pycnogonid with prolonged embryonic development, is described. A staging system comprising ten stages is presented, which can be used in future studies addressing specific developmental processes. The initially slit-like stomodeum anlage forms at the anterior end of an eight-shaped germ band and predates proboscis outgrowth. The latter process is characterized by the protrusion of three cell populations that are subsequently involved in pharynx formation. In later stages, the proboscis assumes distally a horseshoe-like shape. At no time, a structure corresponding to the euarthropod labrum is detectable. Based on the complete lack of palpal and ovigeral embryonic limbs and the early differentiation of walking leg segments 1 and 2, the existence of an embryonized protonymphon stage during callipallenid development is rejected. The evolution of pycnogonid hatching stages, especially within Callipallenidae and Nymphonidae, is re-evaluated in the light of recent phylogenetic analyses. Specifically, the re-emergence of the ancestral protonymphon larva (including re-development of palpal and ovigeral larval limbs) and a possible re-appearance of adult palps in the nymphonid lineage are discussed. This challenges the perception of pycnogonid head appendage evolution as being driven by reduction events alone. © 2011 Springer-Verlag. Source

Brenneis G.,Humboldt University of Berlin | Arango C.P.,Biodiversity Program | Scholtz G.,Humboldt University of Berlin
Development Genes and Evolution | Year: 2011

Pycnogonida (sea spiders) are bizarre marine arthropods that are nowadays most frequently considered as being the sister group to all other chelicerates. The majority of pycnogonid species develops via a protonymphon larva with only three pairs of limbs affiliated with the future head region. Deviating from this, the hatching stage of some representatives shows already an advanced degree of trunk differentiation. Using scanning electron microscopy, fluorescent nucleic staining, and bright-field stereomicroscopy, postembryonic development of Pseudopallene sp. (Callipallenidae), a pycnogonid with an advanced hatching stage, is described. Based on external morphology, six postembryonic stages plus a sub-adult stage are distinguished. The hatching larva is lecithotrophic and bears the chelifores as only functional appendage pair and unarticulated limb buds of walking leg pairs 1 and 2. Palpal and ovigeral larval limbs are absent. Differentiation of walking leg pairs 3 and 4 is sequential. Apart from the first pair, each walking leg goes through a characteristic sequence of three externally distinct stages with two intermittent molts (limb bud-seven podomeres-nine podomeres). First external signs of oviger development are detectable in postembryonic stage 3 bearing three articulated walking leg pairs. Following three more molts, the oviger has attained adult podomere composition. The advanced hatching stages of different callipallenids are compared and the inclusive term "walking leg-bearing larva" is suggested, as opposed to the behavior-based name "attaching larva". Data on temporal and structural patterns of walking leg differentiation in other pycnogonids are reviewed and discussed. To facilitate comparisons of walking leg differentiation patterns across many species, we propose a concise notation in matrix fashion. Due to deviating structural patterns of oviger differentiation in another callipallenid species as well as within other pycnogonid taxa, evolutionary conservation of characteristic stages of oviger development is not apparent even in closely related species. © 2011 Springer-Verlag. Source

Miller T.L.,Biodiversity Program | Bray R.A.,Natural History Museum in London | Cribb T.H.,University of Queensland
Parasitology | Year: 2011

The taxonomy of trematodes of Great Barrier Reef (GBR) fishes has been studied in some detail for over 20 years. Understanding of the fauna has been informed iteratively by approaches to sampling, understanding of morphology, the advent of molecular methodology and a feed-back loop from the emergent understanding of host specificity. Here we analyse 658 host-parasite combinations for 290 trematode species, 152 genera and 28 families from GBR fishes. These are reported from 8 orders, 38 families, 117 genera and 243 species of fishes. Of the 290 species, only 4 (14%) have been reported from more than one order of fishes and just 23 (79%) infect more than one family; 779% of species are known from only one genus, and 60% from only one species of fish. Molecular studies have revealed several complexes of cryptic species and others are suspected; we conclude that no euryxenous host distribution should be accepted on the basis of morphology only. The occurrence of individual trematode species in potential hosts is patchy and difficult to predict reliably a priori or explain convincingly a posteriori. These observations point to the need for a vigorous iterative interaction between the accretion of host specificity data and its interpretation. Copyright © Cambridge University Press 2011. Source

The Polyrhachis xiphias species-group of the subgenus Campomyrma Wheeler is reviewed. Descriptions of the previously-undescribed worker of P. xiphias and queen of P. shixingensis are given. A key to workers of the group is provided. Workers of all species and queens of P. shixingensis and P. xiphias are illustrated. © Rudolf J. Kohout. Source

Polyrhachis (Myrmothrinax) nepenthicola, a new species of the thrinax species-group, is described from Sarawak, Borneo. The characters distinguishing it from similar species of the thrinax-group are provided and the species is illustrated. A preliminary note on its unusual nesting habit is included. Source

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