Early Cambrian arthropods—new insights into arthropod head and structural evolution

Waloszek, Dieter; Chen, Jun-Yuan; Maas, Andreas; Wang, Xiuqiang

doi:10.1016/j.asd.2005.01.005

Cited by 156 publications

(174 citation statements)

References 33 publications

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“…Recent study of fossil arthropods has led to a surprising suggestion that the tripartite brain is not ancient at all. The brain in the first arthropods (known as proarthropods) comprises only two divisions (Waloszek et al, 2005) corresponding to protocerebrum and deuterocerebrum, respectively (Chen, in press). The tritocerebrum brain is a derived character and did not arise until the euarthropod evolutionary stage.…”

Section: Tripartite Brain With Telencephalon Is Not An Ancestral Strumentioning

confidence: 99%

Early crest animals and the insight they provide into the evolutionary origin of craniates

Chen

2008

Genesis

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Summary: The Cristozoa (also known as crest animals) are established as representing the animals containing neural crest and its derivatives, constituting all known craniates and their immediate precraniate precursors. The precraniate crest animals all are extinct and preserved only in Early Cambrian strata of Yunnan (southwestern China). Fine anatomical details of Haikouella and the slightly more advanced species Yunnanozoon exhibit many characters unique to vertebrates, but they lack a skull and most other elaborated placodal and neural crest derivations, throwing novel light onto the previously missing history at the very beginning of cristozoan evolution. Comparative study with the cephalochordate amphioxus suggests that precraniate evolution is marked by a series of innovations including: muscular ventilation with gill-bearing and jointed brachial arches, paired head sensorial organs including paired eyes and nostrils, relatively large, slightly differentiated brain, protovertebrae, and some derivatives of neural crest cells. But, they lack ears, a clear telencephalon, and a skull. Furthermore, comparison of the brains of amphioxus and craniates suggests that the tripartite brain with telencephalon was not an older structure but a novelty of the craniates. genesis 46:623-639,

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Section: Tripartite Brain With Telencephalon Is Not An Ancestral Strumentioning

confidence: 99%

Early crest animals and the insight they provide into the evolutionary origin of craniates

Chen

2008

Genesis

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“…This division between cephalic and locomotory appendage-bearing segments is observed in such iconic Palaeozoic linages as trilobites and 'great-appendage' arthropods (e.g. Anomalocaris), as well as Onychophora, the sister group of Arthropoda [3,4].…”

Section: Introductionmentioning

confidence: 99%

A conserved genetic mechanism specifies deutocerebral appendage identity in insects and arachnids

et al. 2015

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The segmental architecture of the arthropod head is one of the most controversial topics in the evolutionary developmental biology of arthropods. The deutocerebral (second) segment of the head is putatively homologous across Arthropoda, as inferred from the segmental distribution of the tripartite brain and the absence of Hox gene expression of this anterior-most, appendage-bearing segment. While this homology statement implies a putative common mechanism for differentiation of deutocerebral appendages across arthropods, experimental data for deutocerebral appendage fate specification are limited to winged insects. Mandibulates (hexapods, crustaceans and myriapods) bear a characteristic pair of antennae on the deutocerebral segment, whereas chelicerates (e.g. spiders, scorpions, harvestmen) bear the eponymous chelicerae. In such hexapods as the fruit fly, Drosophila melanogaster, and the cricket, Gryllus bimaculatus, cephalic appendages are differentiated from the thoracic appendages (legs) by the activity of the appendage patterning gene homothorax (hth). Here we show that embryonic RNA interference against hth in the harvestman Phalangium opilio results in homeonotic chelicera-to-leg transformations, and also in some cases pedipalp-to-leg transformations. In more strongly affected embryos, adjacent appendages undergo fusion and/ or truncation, and legs display proximal defects, suggesting conservation of additional functions of hth in patterning the antero-posterior and proximodistal appendage axes. Expression signal of anterior Hox genes labial, proboscipedia and Deformed is diminished, but not absent, in hth RNAi embryos, consistent with results previously obtained with the insect G. bimaculatus. Our results substantiate a deep homology across arthropods of the mechanism whereby cephalic appendages are differentiated from locomotory appendages.

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“…Compound eyes exhibiting the ground pattern of the Arthropoda s. str. were most likely stalked (Waloszek et al 2005), a condition also present today in many extant taxa (Fig. 1A, B).…”

mentioning

confidence: 99%

“…Waloszek et al (2005) suggested that anterolateral, possibly compound eyes were likely to be present in the stem species of the Arthropoda s. str. (facets have not yet been found), a taxon including euarthropods, i.e.…”

mentioning

confidence: 99%

Description and interpretation of the internal structure of a Cambrian crustacean compound eye

Schoenemann¹,

Clarkson²,

Castellani³

et al. 2014

Bull. Geosci.

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The exceptionally good preservation of phosphatised, three dimensionally preserved "Orsten" arthropods permits insight into the internal morphology of ancient compound eyes. Analysis, presented here, of the stalked eyes of a Cambrian "Orsten" crustacean reveals structures such as a cornea, a crystalline cone, rhabdomers belonging to possibly five or six sensory cells and an absence of a gap (known as the clear-zone) between dioptric structures and the retina. All these features collectively suggest that this compound eye is of the apposition type. Thus, the principle of mosaic vision likely dates back to Cambrian times, more than half a billion years ago. Using well-established methods this eye can be characterised as dim-light adapted and is likely to have belonged to a benthic organism like many others known from fossils of the Cambrian Alum Shale of Sweden. This seems to be one of the oldest known apposition eyes, and the structural differences between it and eyes more closely conforming to the tetraconate system are likely to be related to the small size of the eye and the photic environment in which it had to operate. Differences from typical compound eye organisation, such as for instance a smaller number of retinula cells than the more typical eight found in most tetraconate arthropods, suggest that either the tetraconate system is not basal and universal, as is often assumed, or that modifications to the system enabling the eye to improve photon capture had already occurred during the Cambrian. •

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Early Cambrian arthropods—new insights into arthropod head and structural evolution

Cited by 156 publications

References 33 publications

Early crest animals and the insight they provide into the evolutionary origin of craniates

Early crest animals and the insight they provide into the evolutionary origin of craniates

A conserved genetic mechanism specifies deutocerebral appendage identity in insects and arachnids

Description and interpretation of the internal structure of a Cambrian crustacean compound eye

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