•The new species possesses a median antenna and large palps on the prostomium
•Neuropodial chaetae are present on the mouth-bearing peristomium
•A chaetigerous origin for the peristomial portion of the annelid head is proposed
Summary
Annelida is one of the most speciose (∼17,000 species) and ecologically successful phyla. Key to this success is their flexible body plan with metameric trunk segments and bipartite heads consisting of a prostomium bearing sensory structures and a peristomium containing the mouth. The flexibility of this body plan has traditionally proven problematic for reconstructing the evolutionary relationships within the Annelida. Although recent phylogenies have focused on resolving the interrelationships of the crown group, many questions remain regarding the early evolution of the annelid body plan itself, including the origin of the head. Here we describe an abundant and exceptionally well-preserved polychaete with traces of putative neural and vascular tissues for the first time in a fossilized annelid. Up to three centimeters in length,Kootenayscolexbarbarensis gen. et sp. nov. is described based on more than 500 specimens from Marble Canyon and several specimens from the original Burgess Shale site (both in British Columbia, Canada). K. barbarensis possesses biramous parapodia along the trunk, bearing similar elongate and thin notochaetae and neurochaetae. A pair of large palps and one median antenna project from the anteriormost dorsal margin of the prostomium. The mouth-bearing peristomium bears neuropodial chaetae, a condition that is also inferred in Canadia and Burgessochaeta from the Burgess Shale, suggesting a chaetigorous origin for the peristomial portion of the head and a secondary loss of peristomial parapodia and chaetae in modern polychaetes.
Keywords: Annelida, polychaete, Burgess Shale, Cambrian Explosion, body plan, prostomium, peristomium, annelid head evolution, Marble Canyon
Life reconstruction of Kootenayscolex barbarensis.
Illustration: Danielle Dufault/Royal Ontario Museum
Kootenayscolex barbarensis is part of a group of animals called annelids (or the 'ringed worms'). It had a pair of long sensory structures called palps on its head, with a small medial antenna between them (right). Its body was covered in fleshy appendages called parapodia which bear bristles called chaetae. These structures are used for movement.
photo: Jean-Bernard Caron/Royal Ontario Museum
Karma Nanglu and Jean-Bernard Caron. 2018. A New Burgess Shale Polychaete and the Origin of the Annelid Head Revisited. Current Biology. 28(2); p319–326.e1. DOI: 10.1016/j.cub.2017.12.019
New 508-million-year-old bristle worm species from British Columbia's Burgess Shale wiggles into evolutionary history phy.so/435841146 via @physorg_com
Half Billion-Year-Old Fossil Clue to How Worms Evolved on.natgeo.com/2n58ibF via @NatGeo
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شاهد قناة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على اليوتيوب لمزيد من الشرح من هنا
رابط مدونة منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات في أي وقت حــــتى لو تم حذفها من هنا شاهد صفحة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على الفيس بوك لمزيد من الشرح من هنا
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ملاحظة هامة: كل عمليات تنزيل، رفع، وتعديل المواضيع الجاهزة تتم بطريقة آلية، ونعتذر عن اي موضوع مخالف او مخل بالحياء مرفوع بالمدونات الجاهزة بآلاف المواضيع والمشاركات، ولكم ان تقوموا بحذف هذه المواضيع والمشاركات والطريقة بسيطة وسهلة. ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــسلامـ.
Chelicerata represents a vast clade of mostly predatory arthropods united by a distinctive body plan throughout the Phanerozoic. Their origins, however, with respect to both their ancestral morphological features and their related ecologies, are still poorly understood. In particular, it remains unclear whether their major diagnostic characters were acquired early on, and their anatomical organization rapidly constrained, or if they emerged from a stem lineage encompassing an array of structural variations, based on a more labile “panchelicerate” body plan.
Results
In this study, we reinvestigated the problematic middle Cambrian arthropod Habelia optata Walcott from the Burgess Shale, and found that it was a close relative of Sanctacaris uncata Briggs and Collins (in Habeliida, ord. nov.), both retrieved in our Bayesian phylogeny as stem chelicerates. Habelia possesses an exoskeleton covered in numerous spines and a bipartite telson as long as the rest of the body. Segments are arranged into three tagmata. The prosoma includes a reduced appendage possibly precursor to the chelicera, raptorial endopods connected to five pairs of outstandingly large and overlapping gnathobasic basipods, antennule-like exopods seemingly dissociated from the main limb axis, and, posteriorly, a pair of appendages morphologically similar to thoracic ones. While the head configuration of habeliidans anchors a seven-segmented prosoma as the chelicerate ground pattern, the peculiar size and arrangement of gnathobases and the presence of sensory/tactile appendages also point to an early convergence with the masticatory head of mandibulates.
Conclusions
Although habeliidans illustrate the early appearance of some diagnostic chelicerate features in the evolution of euarthropods, the unique convergence of their cephalons with mandibulate anatomies suggests that these traits retained an unusual variability in these taxa. The common involvement of strong gnathal appendages across non-megacheirans Cambrian taxa also illustrates that the specialization of the head as the dedicated food-processing tagma was critical to the emergence of both lineages of extant euarthropods—Chelicerata and Mandibulata—and implies that this diversification was facilitated by the expansion of durophagous niches.
Diagnosis (emended from Størmer, 1944). Euarthropods with the following characters: Cephalic shield encompassing at least four pairs of appendages with well-developed endopods; originally, presence along body of at least one pair of appendages with basipod differentiated into a well-sclerotized gnathal sclerite bearing setae or teeth (“gnathobasic appendage”); third gnathobasic cephalic appendage also part of groundplan; post-cephalic endopods terminating in a trident of claws with various arrangements.
Order Habeliida, ord. nov. Aria and Caron
Type family. Habeliidae Simonetta and Delle Cave, 1975.
Other included taxa. Sanctacarididae Legg and Pates, 2016.
Diagnosis. Arachnomorph arthropods with the following characters: Cephalic shield with sub-triangular, sub-horizontal pleural expansions and with antero-lateral notches accommodating pair of lateral compound eyes with no peduncle; cephalic shield with large mesio-dorsal bulge accommodating stomach; five pairs of anterior, slender and segmented antennule-like exopods likely inserted below the eyes and dorsally to other head appendages; on ventral side of head, reduced pair of appendages inserted anteriormost (presumed in Sanctacarididae), followed by five pairs of appendages composed of gnathobasic basipods increasing in size posteriad and bearing seven-segmented spinose/setose enditic endopods projecting anteriad; trunk bearing paddle-like exopods fringed with thin lamellae.
Remarks. We maintain the family Sanctacarididae erected by Legg and Pates [33], since 10 trunk segments and a spatulate telson remain diagnostic of Sanctacaris uncata, Utahcaris orion [33] and Wisangocaris barbarahardyae [35]. The affinity of Messorocaris magna [34] is less clear, but the peculiar shape of its trunk pleurae may place it in its own family.
Habelia had previously been assigned to the orders Aglaspina by Walcott and Emeraldellia by Størmer [36]. Given the lack of cladistic support for these taxa, which would be para- or polyphyletically nested within Arachnomorpha, the lack of redescription for Molaria, and the fact that their diagnoses should be extensively revised in light of the new data gathered on aglaspidids and Emeraldella, we have not reused Aglaspina or Emeraldellia herein.
Family Habeliidae Simonetta and Delle Cave, 1975. Type genus.Habelia Walcott, 1912.
Diagnosis. Habeliidan euarthropods with the following characters: Body elongate, 19-segmented, divided into three distinct tagmata: cephalon (or “prosoma”) of seven segments (or eight somites) and trunk (12 segments) composed of a five-segmented thorax (or “mesosoma”) and eight-segmented post-thorax (or “metasoma”); trunk tagmatization based on discrete limb differentiation between thorax and post-thorax; posteriormost cephalic appendage (7th) similar to thoracic appendages, all characterized by a cheiromorph morphology: large undifferentiated basipods, well-developed seven-segmented endopods without endites, and paddle-like exopods fringed with oblanceolate lamellae; telson elongate.
Remarks. We hereby establish a diagnosis for the family Habeliidae, as the original publication of the taxon was not associated with one [39]; we also formalize diagnoses and descriptions for Habelia optata hereafter. The genus Thelxiope was also included in Habeliidae by Simonetta and Delle Cave; however, the presence of eight post-cephalic tergites and a pygidium would rather seem to indicate a relationship with Mollisonia [54, 55]. Thelxiope is therefore removed from Habeliidae.
Genus Habelia Walcott, 1912.
Type species.Habelia optata Walcott, 1912.
Diagnosis. Habeliid arthropod with the following characters: Post-ocular lateral and postero-lateral cephalic margins as well as pleural margins of trunk segments adorned with triangular spines; cuticular surface of cephalon and posterior portion of trunk segments richly adorned with small blunt spines/tubercles; cephalic gnathobases with elongate proximal “arm”; gnathobasic teeth differentiated antero-posteriorly (slender and long to short and stout); cephalic endopods with setal brush on podomeres 5 and 6; five-segmented thorax bearing strong biramous appendages with robust, clawed endopods and long basipods; very long (subequal to slightly greater than head and trunk length) bipartite telson, with a long, dentate proximal portion adorned with lateral spines, and a short distal portion about 1/3rd as long as proximal portion.
Cédric Aria and Jean-Bernard Caron. 2017. Mandibulate Convergence in An Armoured Cambrian Stem Chelicerate. BMC Evolutionary Biology. 17:261. DOI: 10.1186/s12862-017-1088-7
A 508-million-year-old sea predator with a 'jackknife' head phy.so/433048787@physorg_com
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رابط مدونة منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات في أي وقت حــــتى لو تم حذفها من هنا شاهد صفحة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على الفيس بوك لمزيد من الشرح من هنا
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ملاحظة هامة: كل عمليات تنزيل، رفع، وتعديل المواضيع الجاهزة تتم بطريقة آلية، ونعتذر عن اي موضوع مخالف او مخل بالحياء مرفوع بالمدونات الجاهزة بآلاف المواضيع والمشاركات، ولكم ان تقوموا بحذف هذه المواضيع والمشاركات والطريقة بسيطة وسهلة. ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــسلامـ.
Symbiotic relationships are widespread in terrestrial and aquatic animals today, but evidence of symbiosis in the fossil record between soft-bodied bilaterians where the symbiont is intimately associated with the integument of the host is extremely rare. The radiation of metazoan life apparent in the Ediacaran (~635–541 million years ago) and Cambrian (~541–488 million years ago) periods is increasingly accepted to represent ecological diversification resulting from earlier key genetic developmental events and other innovations that occurred in the late Tonian and Cryogenian periods (~850–635 million years ago). The Cambrian has representative animals in each major ecospace category, the early Cambrian in particular having witnessed the earliest known complex animal communities and trophic structures, including symbiotic relationships. Here we report on newly discovered Cricocosmia and Mafangscolex worms that are hosts to aggregates of a new species of tiny worm in the lower Cambrian (Series 2, Stage 3) Chengjiang Lagerstätte of Yunnan Province, southwest China. The worm associations suggest the earliest known record of aggregate infestation of the integument of a soft-bodied bilaterian, host specificity and host shift.
Fig. 1: Cluster of Inquicus fellatus attached to Cricocosmia jinningensis. a, C. jinningensis (YKLP 13226a) with a minimum of 12 attached I. fellatus (YKLP 13235–13246) on the ventral side. Scale bar: 3 mm.
Clade Bilateria
Clade Protostomia
Inquicus fellatus gen. et sp. nov.
Etymology. Genus name from inquilinus (Latin) meaning a ‘lodger’ or ‘dweller in another’s house’, plus priscus ‘ancient’. Species from fellator ‘a sucker’ and atus ‘provided with’, alluding to its lifestyle.
Holotype. YKLP 13235 (part and counterpart). A complete speci-men, 3.3 mm long, attached to a Cricocosmia jinningensis specimen, YKLP 13226. Eleven other specimens of I. fellatus (YKLP 13236–13246) are attached to this host.
Horizon. Yu’anshan Member, Chiungchussu Formation, Eoredlichia–Wutingaspis trilobite biozone, Nangaoan Stage of Chinese regional usage, Cambrian Series 2; Stage 3 (ref. 1).
Diagnosis for genus (monotypic) and species. Small, ‘bowling-pin’-shaped worm with a sub-circular-shaped attachment disc at the posterior end of the body and a through gut that is funnel-shaped anteriorly. At the end of the gut near the attachment disc, there is a tiny sub-circular structure, interpreted as the urogenital opening or anus.
Artist's reconstruction of the worm-like animal Inquicus fellatus, infesting Cricocosmia jinningensis, a marine worm that lived in seafloor sediments more than 500 million years ago.
Peiyun Cong, Xiaoya Ma, Mark Williams, David J. Siveter, Derek J. Siveter, Sarah E. Gabbott, Dayou Zhai, Tomasz Goral, Gregory D. Edgecombe and Xianguang Hou. 2017. Host-Specific Infestation in early Cambrian Worms. Nature Ecology & Evolution. DOI: 10.1038/s41559-017-0278-4
One of the earliest examples of a symbiotic relationship between invertebrates has been found in 520-million-year-old fossils from China.
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شاهد قناة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على اليوتيوب لمزيد من الشرح من هنا
رابط مدونة منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات في أي وقت حــــتى لو تم حذفها من هنا شاهد صفحة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على الفيس بوك لمزيد من الشرح من هنا
تعرف على ترتيب مواضيع منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات (حتى لا تختلط عليك الامور) من هنا
ملاحظة هامة: كل عمليات تنزيل، رفع، وتعديل المواضيع الجاهزة تتم بطريقة آلية، ونعتذر عن اي موضوع مخالف او مخل بالحياء مرفوع بالمدونات الجاهزة بآلاف المواضيع والمشاركات، ولكم ان تقوموا بحذف هذه المواضيع والمشاركات والطريقة بسيطة وسهلة. ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــسلامـ.
• Multiple specimens of a new Cambrian chaetognath preserve evidence of soft tissues
• At ∼10 cm long, it is one of the largest chaetognaths known, living or fossil
• The grasping apparatus is unique in bearing as many as 25 spines in each half
• Chaetognaths may have been benthic before becoming important planktonic predators
Summary
Chaetognaths (arrow worms) are a separate phylum (Chaetognatha) of small carnivorous animals, dominantly pelagic, and a major component of today’s plankton. The position of Chaetognatha among metazoan phyla remains equivocal—neither morphological nor molecular data provide definitive evidence. Originating early in the Cambrian period, if not earlier, chaetognaths quickly became important members of marine metazoan communities. Chaetognath grasping spines, originally reported as conodonts, occur worldwide in many Cambrian marine sediments. Fossilized chaetognath bodies, in contrast, are very rare: only two unequivocal specimens have been reported, both from the early Cambrian of China. Here we describeCapinatator praetermissus, a new genus and species, based on ∼50 specimens from several middle Cambrian Burgess Shale localities in British Columbia, many of which preserve evidence of soft tissues. Capinatator praetermissus reached body lengths of nearly 10 cm exclusive of fins, a much larger size than that of most living forms. Clusters of specimens preserving the body indicate that they were rapidly buried, providing indirect evidence that they swam near the seabed. The feeding apparatus comprises up to ∼25 spines in each half, almost double the maximum number in living chaetognaths. Early chaetognaths apparently occupied ecological niches associated with predatory euarthropods. The large body size and high number of grasping spines in C. praetermissus may indicate that miniaturization and migration to a planktonic lifestyle were secondary.
Of the specimens studied, many preserve the feeding apparatus attached to the head, with some showing evidence of the rest of the body. Forty-eight specimens are held by the Royal Ontario Museum and one, with an isolated set of grasping appendages, is from the Smithsonian National Museum of Natural History. Specimen from the Collins Quarry, Mount Stephen (Yoho National Park, BC). (Photo by J.B. Caron/Royal Ontario Museum)
Figure 4. Life Reconstruction of Capinatator praetermissus,The location, size, and shape of the fins are speculative.
Drawing by Marianne Collins/Royal Ontario Museum.
The generic name is derived from capio, to grasp and natator, swimmer, reflecting its predatory habit. The species name praetermissus, overlooked, refers to the long gestation between discovery and description: a few specimens were found more than 30 years ago by the Royal Ontario Museum (ROM) during early exploration for new Burgess Shale sites in the Canadian Rockies.
Derek E.G. Briggs and Jean-Bernard Caron. 2017. A Large Cambrian Chaetognath with Supernumerary Grasping Spines. Current Biology. in press. DOI: 10.1016/j.cub.2017.07.003
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شاهد قناة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على اليوتيوب لمزيد من الشرح من هنا
رابط مدونة منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات في أي وقت حــــتى لو تم حذفها من هنا شاهد صفحة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على الفيس بوك لمزيد من الشرح من هنا
تعرف على ترتيب مواضيع منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات (حتى لا تختلط عليك الامور) من هنا
ملاحظة هامة: كل عمليات تنزيل، رفع، وتعديل المواضيع الجاهزة تتم بطريقة آلية، ونعتذر عن اي موضوع مخالف او مخل بالحياء مرفوع بالمدونات الجاهزة بآلاف المواضيع والمشاركات، ولكم ان تقوموا بحذف هذه المواضيع والمشاركات والطريقة بسيطة وسهلة. ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــسلامـ.
We describe the exceptionally well‐preserved non‐trilobite artiopodanZhiwenia coronata gen. et sp. nov. from the Cambrian Stage 3 Xiaoshiba Lagerstätte in Yunnan, China. The exoskeleton consists of a cephalic shield with dorsal sutures expressed as lateral notches that accommodate stalked lateral eyes, an elongate trunk composed of 20 tergites—the first of which is reduced—and a short tailspine with marginal spines. Appendicular data include a pair of multi‐segmented antennae, and homonomous biramous trunk limbs consisting of an endopod with at least seven podomeres and a flattened exopod with lamellae. Although the presence of cephalic notches and a reduced first trunk tergite invites comparisons with the petalopleurans Xandarella, Luohiniella and Cindarella, the proportions and exoskeletal tagmosis of Zhiwenia do not closely resemble those of any major group within Trilobitomorpha. Parsimony and Bayesian phylogenetic analyses consistently support Zhiwenia as sister‐taxon to the Emu Bay Shale artiopodan Australimicola spriggi, and both of them as closely related to Acanthomeridion from the Chengjiang. This new monophyletic clade, Protosutura nov., occupies a basal phylogenetic position within Artiopoda as sister‐group to Trilobitomorpha and Vicissicaudata, illuminates the ancestral organization of these successful euarthropods, and leads to a re‐evaluation of the evolution of ecdysial dorsal sutures within the group.
Fig. 2. Completely articulated specimen ofZhiwenia coronata gen. et sp. nov. from the Cambrian Stage 3 Xiaoshiba Lagerst€atte. (a) YKLP 12370 Holotype, dorsal view of a complete individual. (b) Interpretative diagram.
Fig. 5. Morphological reconstruction of Zhiwenia coronata gen. et sp. nov. from the Xiaoshiba Lagerst€atte.
Euarthropoda Lankester, 1904 (see discussion in Ortega-Hernandez, 2016)
Artiopoda Hou and Bergstrom, 1997 (see also Stein € and Selden, 2012).
Protosutura nov.
Diagnosis. Non-biomineralized artiopodan euarthropods characterized by a short semicircular cephalic shield with simple dorsal ecdysial sutures located on either side of the head (secondarily lost in some representatives). Trunk elongate and with homonomous construction, consisting exclusively of freely articulating tergites of subequal length that convey a subrectangular to suboval exoskeletal outline. Posterior trunk tergites strongly curved. Tailspine spinose and short—less than half the trunk length—occasionally bearing marginal spines of variable number and size.
Etymology. Derived from the Greek prefix proto (first, primitive), and the Latin root sutura, referencing the presence of dorsal ecdysial sutures on the head shield.
Included taxa. Acanthomeridion serratum Hou et al., 1989; Acanthomeridion anacanthus Hou et al., 2017; Australimicola spriggi Paterson et al., 2012; Zhiwenia coronata gen. et. sp. nov.
Zhiwenia coronatagen. et. sp. nov.
Type species, locality and stratigraphy.Zhiwenia coronata gen. et. sp. nov. from the Xiaoshiba section (Fig. 1), Kunming, Yunnan; Cambrian Stage 3 Hongjingshao Formation, Yunnanocephalus– Chengjiangaspis–Hongshiyanaspis Biozone (Yang et al., 2013, 2014, 2015, 2016a, b, 2018).
Etymology. The new genus is named in memory of Professor Zhi-Wen Jiang for his contributions to microfossils and biostratigraphy of Yunnan Province; coron (Latin), crown, referring to the shape of the two-notch bearing cephalic shield.
Fig. 6. Results of parsimony and Bayesian phylogenetic analyses. All trees depict a strict consensus. Asterisks indicate presence of dorsal ecdysial sutures on cephalic shield. (c) Implied weight parsimony, k = 5, 10 (1 MPT, CI = 0.41, RI = 0.73).
Kun‐Sheng Du, Javier Ortega‐Hernández, Jie Yang and Xi‐Guang Zhang. 2018. A Soft‐bodied Euarthropod from the early Cambrian Xiaoshiba Lagerstätte of China supports A New Clade of Basal Artiopodans with Dorsal Ecdysial Sutures. Cladistics. DOI: 10.1111/cla.12344
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شاهد قناة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على اليوتيوب لمزيد من الشرح من هنا
رابط مدونة منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات في أي وقت حــــتى لو تم حذفها من هنا شاهد صفحة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على الفيس بوك لمزيد من الشرح من هنا
تعرف على ترتيب مواضيع منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات (حتى لا تختلط عليك الامور) من هنا
ملاحظة هامة: كل عمليات تنزيل، رفع، وتعديل المواضيع الجاهزة تتم بطريقة آلية، ونعتذر عن اي موضوع مخالف او مخل بالحياء مرفوع بالمدونات الجاهزة بآلاف المواضيع والمشاركات، ولكم ان تقوموا بحذف هذه المواضيع والمشاركات والطريقة بسيطة وسهلة. ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــسلامـ.
•The new species possesses a median antenna and large palps on the prostomium
•Neuropodial chaetae are present on the mouth-bearing peristomium
•A chaetigerous origin for the peristomial portion of the annelid head is proposed
Summary
Annelida is one of the most speciose (∼17,000 species) and ecologically successful phyla. Key to this success is their flexible body plan with metameric trunk segments and bipartite heads consisting of a prostomium bearing sensory structures and a peristomium containing the mouth. The flexibility of this body plan has traditionally proven problematic for reconstructing the evolutionary relationships within the Annelida. Although recent phylogenies have focused on resolving the interrelationships of the crown group, many questions remain regarding the early evolution of the annelid body plan itself, including the origin of the head. Here we describe an abundant and exceptionally well-preserved polychaete with traces of putative neural and vascular tissues for the first time in a fossilized annelid. Up to three centimeters in length,Kootenayscolexbarbarensis gen. et sp. nov. is described based on more than 500 specimens from Marble Canyon and several specimens from the original Burgess Shale site (both in British Columbia, Canada). K. barbarensis possesses biramous parapodia along the trunk, bearing similar elongate and thin notochaetae and neurochaetae. A pair of large palps and one median antenna project from the anteriormost dorsal margin of the prostomium. The mouth-bearing peristomium bears neuropodial chaetae, a condition that is also inferred in Canadia and Burgessochaeta from the Burgess Shale, suggesting a chaetigorous origin for the peristomial portion of the head and a secondary loss of peristomial parapodia and chaetae in modern polychaetes.
Keywords: Annelida, polychaete, Burgess Shale, Cambrian Explosion, body plan, prostomium, peristomium, annelid head evolution, Marble Canyon
Life reconstruction of Kootenayscolex barbarensis.
Illustration: Danielle Dufault/Royal Ontario Museum
Kootenayscolex barbarensis is part of a group of animals called annelids (or the 'ringed worms'). It had a pair of long sensory structures called palps on its head, with a small medial antenna between them (right). Its body was covered in fleshy appendages called parapodia which bear bristles called chaetae. These structures are used for movement.
photo: Jean-Bernard Caron/Royal Ontario Museum
Karma Nanglu and Jean-Bernard Caron. 2018. A New Burgess Shale Polychaete and the Origin of the Annelid Head Revisited. Current Biology. 28(2); p319–326.e1. DOI: 10.1016/j.cub.2017.12.019
New 508-million-year-old bristle worm species from British Columbia's Burgess Shale wiggles into evolutionary history phy.so/435841146 via @physorg_com
Half Billion-Year-Old Fossil Clue to How Worms Evolved on.natgeo.com/2n58ibF via @NatGeo
كيف تحصل على مدونة جاهزة بآلاف المواضيع والمشاركات من هنا
شاهد قناة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على اليوتيوب لمزيد من الشرح من هنا
رابط مدونة منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات في أي وقت حــــتى لو تم حذفها من هنا شاهد صفحة منتدى مدونات بلوجر جاهزة بألاف المواضيع والمشاركات على الفيس بوك لمزيد من الشرح من هنا
تعرف على ترتيب مواضيع منتدى مدونات بلوجر جاهزة بآلاف المواضيع والمشاركات (حتى لا تختلط عليك الامور) من هنا
ملاحظة هامة: كل عمليات تنزيل، رفع، وتعديل المواضيع الجاهزة تتم بطريقة آلية، ونعتذر عن اي موضوع مخالف او مخل بالحياء مرفوع بالمدونات الجاهزة بآلاف المواضيع والمشاركات، ولكم ان تقوموا بحذف هذه المواضيع والمشاركات والطريقة بسيطة وسهلة. ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــسلامـ.
