Morphology of Anomalocaris canadensis from the Burgess Shale

2014 ◽  
Vol 88 (1) ◽  
pp. 68-91 ◽  
Author(s):  
Allison C. Daley ◽  
Gregory D. Edgecombe
Keyword(s):  
Close Association ◽  
Dorsal Surface ◽  
Ventral Surface ◽  
The Body ◽  
Body Region ◽  
Morphological Description ◽  
Burgess Shale ◽  
Oral Cone ◽  
Stem Lineage ◽  
Posterior Body Region

Recent description of the oral cone of Anomalocaris canadensis from the Burgess Shale (Cambrian Series 3, Stage 5) highlighted significant differences from published accounts of this iconic species, and prompts a new evaluation of its morphology as a whole. All known specimens of A. canadensis, including previously unpublished material, were examined with the aim of providing a cohesive morphological description of this stem lineage arthropod. In contrast to previous descriptions, the dorsal surface of the head is shown to be covered by a small, oval carapace in close association with paired stalked eyes, and the ventral surface bears only the triradial oral cone, with no evidence of a hypostome or an anterior sclerite. The frontal appendages reveal new details of the arthrodial membranes and a narrower cross-section in dorsal view than previously reconstructed. The posterior body region reveals a complex suite of digestive, respiratory, and locomotory characters that include a differentiated foregut and hindgut, a midgut with paired glands, gill-like setal blades, and evidence of muscle bundles and struts that presumably supported the swimming movement of the body flaps. The tail fan includes a central blade in addition to the previously described three pairs of lateral blades. Some of these structures have not been identified in other anomalocaridids, making Anomalocaris critical for understanding the functional morphology of the group as a whole and corroborating its arthropod affinities.

scholarly journals The ocellate river stingray (Potamotrygon motoro) exploits vortices of sediment to bury into the substrate

2019 ◽  
Author(s):  
S.G. Seamone ◽  
D.A. Syme
Keyword(s):  
Particle Image ◽  
Dorsal Surface ◽  
Ventral Surface ◽  
The Body ◽  
Effective Control ◽  
Posterior Portion ◽  
Dorsal Midline ◽  
Pectoral Fins ◽  
Image Velocimetry ◽  
Sediment Flow

ABSTRACTParticle image velocimetry and video analysis were employed to discern and describe the mechanism used by the stingray Potamotrygon motoro to bury into the substrate. P. motoro repeatedly and rapidly pumped the body up and down while folding the posterior portion of the pectoral fins up and over, drawing water in and suspending sediment beneath the pectoral disc. As the fins folded up and over, vortices of fluidized sediment travelled along the ventral surface of the fins toward the fin tips, and were then directed onto the dorsal surface of the fins and towards the dorsal midline of the fish, where they dissipated and the sediment settled over the dorsal surface of the ray. As displacement and speed of the body pumping and finbeat motions increased, the speed of the sediment translating across the dorsal surface increased, and accordingly, sediment coverage of the dorsal surface increased. Mean sediment coverage was 82.5% ± 3.0 S.E.M, and appeared to be selectively controlled, whereby the pectoral fins tended to bury more than the body, head and tail, and the body more than the head and the tail. In the most vigorous burying events, vortices of sediment shed from each fin collided at the midline and annihilated, reorienting the sediment flow and sending jets of sediment towards the head and the tail, covering these locations with sediment. Hence, this study demonstrates that the mechanism of burying employed by P. motoro permits effective control of sediment vortices and flows to modulate the extent of burying.

The reactions to carcinogens in the axolotl (Ambystoma mexicanum) in relation to the ‘regeneration field control’ hypothesis

Development ◽  
1971 ◽  
Vol 26 (3) ◽  
pp. 425-441
Author(s):  
Andrew J. Ingram
Keyword(s):  
Body Wall ◽  
Intradermal Injection ◽  
Ambystoma Mexicanum ◽  
The Body ◽  
Body Region ◽  
Initial Reaction ◽  
Wound Healing Response ◽  
Field Control ◽  
Control Hypothesis ◽  
Posterior Body Region

About 200 axolotls, between 5 and 21 months old, were treated in the body wall with carcinogens or control substances, by subcutaneous or intradermal injection, or by subcutaneous implantation. In response to an injection of dibenzanthracene in olive oil an initial reaction appeared within 13 days. This consisted of an epidermal proliferation and a subcutaneous infiltration of macrophages. The epidermis returned to normal after several weeks, but the subcutaneous response took 6 months to disappear. The initial reaction appeared to be, at least partially, a wound healing response; its regression could not have been due to regeneration field control as it occurred in the posterior body region. Following the disappearance of the initial reaction a secondary reaction of papilloma-like outgrowths arose between 7 and 20 months after injection. Of the axolotls surviving for a sufficient length of time, outgrowths arose in 14 out of 54 animals injected with dibenzanthracene and in 18 out of 57 sites injected with methylcholanthrene. These outgrowths had some features in common with the papillomata of mice, but none have yet progressed to carcinomata. In a group of axolotls injected in three different regions the frequency of outgrowths varied according to the sites; however, this was thought to be due to differences in the difficulty of injecting the three regions. Two tumours, a sarcoma and a hepatoma, arose in the course of these experiments, 3 and 2 years respectively after carcinogen treatment. From this it is suggested tentatively that tumour induction by polycyclic hydrocarbons in the axolotl may require a long latent period and involve a low tumour incidence; however, it is possible that at least one of the tumours was not induced by the treatment.

The Middle Cambrian metazoan Wiwaxia corrugata (Matthew) from the Burgess Shale and Ogygopsis Shale, British Columbia, Canada

1985 ◽  
Vol 307 (1134) ◽  
pp. 507-582 ◽  
Keyword(s):  
Ventral Surface ◽  
The Body ◽  
Feeding Apparatus ◽  
Burgess Shale ◽  
Significant Similarity ◽  
Middle Cambrian ◽  
Stages Of Growth ◽  
Sea Bed ◽  
Juvenile Specimen ◽  
Early Metazoan

A detailed redescription of the Middle Cambrian metazoan Wiwaxia corrugata (Matthew) is given with the aid of photographs, mostly taken under ultraviolet radiation, and explanatory camera lucida drawings. Wiwaxia is known only from the Stephen Formation with four localities within the Bathyuriscus-Elrathina Zone, the celebrated Burgess Shale (Phyllopod bed) and Ogygopsis Shale and two localities that appear to expose strata relatively high in the Formation, and a new locality in the underlying Glossopleura Zone. Specimens from the Ogygopsis Shale consist almost entirely of isolated sclerites, whereas in the Phyllopod bed the species is also known from entire specimens, semi-isolated assemblages and isolated soft-parts. T he description here is based almost entirely on Phyllopod bed m aterial. Wiwaxia was originally largely covered by sclerites. On the basis of shape and arrangement five distinct zones are recognizable: dorsal, upper lateral, lower lateral, anterior and ventro-lateral. In addition, there was a row of elongate dorso-lateral spinose sclerites running along either side of the body. Each sclerite was inserted separately via a root-like structure. Growth of the animal appears to have occurred by moulting of the sclerites; one unique juvenile specimen appears to be preserved in the act of moulting. The ventral surface was apparently an area of soft tissue devoid of sclerites. Little is known of the internal anatomy, although anteriorly there was a feeding apparatus consisting of two rows of posteriorly directed teeth. Most stages of growth are known varying from presumed juveniles, which at their smallest may have lacked spines, to adults over 50 mm long. Wiwaxia appears to have been an epifaunal deposit feeder that crawled across the sea-bed, although smaller juveniles may have been infaunal. The dorso-lateral spines may have provided protection against predators and the existence of broken spines suggests the successful deterrence of attack. The affinities of Wiwaxia do not appear to lie with the polychaetous annelids. While the possibilities of convergence cannot be eliminated, there appears to be a significant similarity between Wiwaxia and molluscs that suggests a related derivation from a turbellarian ancestor. Nevertheless, Wiwaxia has a distinctive bodyplan and as such cannot be accommodated in any known phylum. While Wiwaxia is unique to the Stephen Formation isolated sclerites from Lower Cambrian rocks appear to represent earlier wiwaxiids, although these sclerites show differences in their size and composition as com pared with Wiwaxia . Wiwaxia enhances knowledge of early metazoan evolution and ecology in the Cambrian. In particular, it gives fresh insights into the origin and relative success of certain metazoan bodyplans, the origin of trace fossils, and the importance of predation in Cambrian communities.

scholarly journals AN ANTS'-NEST COCCID FROM NEW MEXICO

1898 ◽  
Vol 30 (2) ◽  
pp. 47-48 ◽  
Author(s):  
J. B. Tinsley
Keyword(s):  
New Mexico ◽  
Dorsal Surface ◽  
Ventral Surface ◽  
The Body ◽  
Naked Eye ◽  
Average Size

Adult ♀.—Length, 5 mm.; width, 3 mm.; many are smaller than this, but this seems to be the average size of the adult containing eggs. Colour yellowish-gray, although they appear light gray, from the mealy secretion which covers the body.Shape, ellipsoidal, dorsal surface quite convex, ventral surface flat, extremities rather pointed. segmentation quite distinct to naked eye. Extremely short lateral appendages, little projections just visible; caudal appendages a little longer.

scholarly journals Myogenesis of Siboglinum Fiordicum Sheds Light on Body Regionalisation in Beard Worms (Siboglinidae, Annelida)

2021 ◽  
Author(s):  
Nadezhda Nikolaevna Rimskaya-Korsakova ◽  
Nadezda Karaseva ◽  
Timofei Pimenov ◽  
Hans Tore Rapp ◽  
Eve Southward ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
The Body ◽  
Body Region ◽  
Body Regions ◽  
Transmission Electron ◽  
Chaetopterus Variopedatus ◽  
Anterior Body ◽  
Longitudinal Muscles ◽  
Posterior Body Region

Abstract BackgroundMany annelids, including well-studied species such as Platynereis, show similar structured segments along their body axis (homonomous segmentation). However, numerous annelid species diverge from this pattern and exhibit specialised segments or body regions (heteronomous segmentation). Recent phylogenomic studies and paleontological findings suggest that a heteronomous body architecture may represent an ancestral condition in Annelida. To better understand the segmentation within heteronomous species we describe the myogenesis and mesodermal delineation of segments in Siboglinum fiordicum during development. ResultsEmploying confocal and transmission electron microscopy we show that the somatic circular musculature lies inside the longitudinal musculature and is predominantly developed at the anterior end of the larva. The longitudinal musculature consists of four separate strands at the ventral, dorsal, and ventrolateral body sides. Posteriorly, the longitudinal strands form a continuous layer. Our application of transmission electron microscopy allows us to describe the developmental order of the non-muscular septa. The first septum to form is supported by thick bundles of longitudinal muscles and separates the body into an anterior and a posterior region. The second group of septa to develop further divides the posterior body region (opisthosoma) and is supported by developing circular muscles. At the late larval stage, a septum reinforced by circular muscles divides the anterior body region into a forepart and a trunk segment. The remaining septa and their circular muscles form one by one at the very posterior end of the opisthosoma. Functionally, the prominent ventrolateral longitudinal muscles in the larva are proposed to drive the search movements of the head, while the anterior circular muscles and the posterior continuous layers of longitudinal muscles support the burrowing behaviour of the larva.ConclusionsThe heteronomous Siboglinum lacks the strict anterior to posterior sequence of segment formation as it is found in the most studied annelid species. Instead, the first septum divides the body into two body regions, before segments are layed down in first the posterior opisthosoma and then in the anterior body, respectively. Similar pattern of segment formation is described for the heteronomous chaetopterid Chaetopterus variopedatus and may represent an ancestral segmentation process in Annelida.

The Blood Vascular System of Nephtys (Annelida, Polychaeta)

1956 ◽  
Vol s3-97 (38) ◽  
pp. 235-249
Author(s):  
R. B. CLARK
Keyword(s):  
Body Wall ◽  
Vascular System ◽  
Close Association ◽  
Circulatory System ◽  
Ventral Surface ◽  
Blood Stream ◽  
Neurosecretory Cells ◽  
The Body ◽  
Dorsal Vessel ◽  
The Brain

The four longitudinal vessels of the circulatory system of Nephtys californiensis are dorsal, sub-intestinal, and neural, the latter being paired. There is a complete longitudinal circulation; the dorsal vessel communicates with the sub-intestinal by way of the proboscidial circulation and with the neural by way of the circum-oral vessels. In each middle and posterior segment segmental vessels from each of the longitudinal trunks carry blood to and from the parapodia and body-wall. The segmental circulation is completed by a circum-intestinal vessel connecting the dorsal and subintestinal vessels in each segment and an intersegmental branch connecting the dorsal and sub-intestinal segmental vessels. A trans-septal branch of the neural segmental vessel communicates with the sub-intestinal segmental vessel. This arrangement is modified in anterior segments which house the muscular, eversible pharynx, and no blood-vessels cross the coelom except by running through the body-wall. On anatomical grounds and by comparison with other polychaetes it seems likely that segmental is subordinate to longitudinal circulation. There are no endothelial capillaries such as have been described in some other polychaetes; instead there are numerous blindending vessels the walls of which are composed of the same three layers as other vessels and which are probably contractile. The dorsal vessel, where it is in contact with the ventral surface of the supra-oesophageal ganglion, forms a plexus in close association with a modified part of the brain capsule and a special axonal tract within the ganglion. It is thought that by way of this ‘cerebro-vascular complex’, hormones produced in the neurosecretory cells of the brain pass into the blood-stream.

Gross morphological studies on the sternum of crested serpent eagle (Spilornis cheela)

2019 ◽  
Author(s):  
O.P. Choudhary ◽  
P.C. Kalita ◽  
T.K. Rajkhowa ◽  
R.S. Arya ◽  
A. Kalita ◽  
...  
Keyword(s):  
Morphological Characteristics ◽  
Dorsal Surface ◽  
Ventral Surface ◽  
The Body ◽  
Median Line ◽  
Lateral Border ◽  
Lateral Process ◽  
Morphological Studies ◽  
Quadrilateral Plate ◽  
Flat Bone

The present study was designed to elucidate the morphological characteristics of sternum of crested serpent eagle. The sternum was a thin, flat bone with a body, rostrum and keel. The body was quadrilateral plate with concave dorsal and convex ventral surfaces and four borders. Numerous pneumatic foramina were present on the dorsal surface. The ventral surface presented a large, boat shaped keel along its median line. The cranial border was convex and thick and two pneumatic foramina were present behind the cranial border on the ventral surface of sternum. The facets for coracoid bones were located just below the cranial border. The lateral border on either side presented six articular facets for sternal ribs. The triangular pointed cranio-lateral process was observed at the junction of cranial and lateral border on either side. The caudal border was convex and caudo-lateral processes were absent. Two distinct oval foramina were seen near the caudal border. The rostrum or sternal spine was smaller and located just below the cranial border of the body of the sternum. The sternum presented a well-developed triangular keel located along the midline of the ventral surface of the body of sternum.

Ektaphelenchoides shiroodensis n. sp. (Rhabditida: Ektaphelenchinae) a new member of the genus

Nematology ◽  
2020 ◽  
Vol 22 (5) ◽  
pp. 493-503 ◽  
Author(s):  
Farzad Aliramaji ◽  
Ebrahim Pourjam ◽  
Majid Pedram
Keyword(s):  
New Species ◽  
Phylogenetic Analyses ◽  
Large Subunit ◽  
The Body ◽  
Body Region ◽  
Lsu Rdna ◽  
Similar Species ◽  
Mazandaran Province ◽  
Lateral Field ◽  
Posterior Body Region

Summary Ektaphelenchoides shiroodensis n. sp. is described and illustrated based upon morphological, morphometric and molecular data. It was recovered from the bark samples of a dead alder tree (Alnus sp.) from countryside around Shirood city, Mazandaran province, in the north of Iran. The new species is characterised by 768-985 μm long females, its lip region separated from the body contour by constriction, lateral field with three barely visible lines, forming two weak bands, 26-29 μm long stylet with wide lumen without conophore and basal swellings, excretory pore always at the level with median bulb, post-vulval uterine sac (PUS) 43-76 μm long, elongate conoid posterior body region ending to a long filiform part with pointed tip, males common with dorsally convex conical tail ending to a short narrower region with pointed tip, seven precloacal + cloacal + caudal papillae and arcuate spicules with wide condylus, blunt rostrum and simple end. Based upon the similar posterior body region (‘tail’) and comparable PUS length, the new species was compared to three known species, viz., E. attenuata, E. hunti and E. pini. Comparisons with the aforementioned species and similar species under the genus Seinura are discussed. The phylogenetic affinities of the new species, based upon two partial small and large subunit ribosomal DNA (SSU and LSU rDNA D2-D3) sequences, are discussed. Furthermore, several ektaphelenchid and seinurid species previously described from Iran were recovered in the present study, sequenced for their aforementioned genomic markers, and included in the phylogenetic analyses.

Re-discovery and novel contributions to morphology and multigene phylogeny of Myxophyllum steenstrupi (Ciliophora: Pleuronematida), an obligate symbiont of terrestrial pulmonates

2020 ◽  
Author(s):  
Tengyue Zhang ◽  
Peter Vďačný
Keyword(s):  
Phylogenetic Analyses ◽  
Mantle Cavity ◽  
The Body ◽  
Body Region ◽  
Multigene Phylogeny ◽  
Nuclear Markers ◽  
Free Living ◽  
Obligate Symbiont ◽  
First Time ◽  
Posterior Body Region

Abstract Myxophyllum steenstrupi is a symbiotic ciliate living in the body slime and mantle cavity of terrestrial pulmonates (Gastropoda: Pulmonata). In the present study, M. steenstrupi was re-discovered after almost 30 years and characterized using an integrative morpho-molecular approach for the first time. Myxophyllum is distinguished by a broadly ovate, about 140 × 115 μm-sized body, a nuclear apparatus typically composed of seven macronuclear nodules and a single micronucleus, a central contractile vacuole, a shallow oral cavity situated in the posterior body region and dense somatic ciliature with extensive thigmotactic field. According to the present phylogenetic analyses of two mitochondrial and five nuclear markers, M. steenstrupi is classified in the predominantly free-living order Pleuronematida (Oligohymenophorea: Scuticociliatia). This order also encompasses other taxa isolated from molluscs and traditionally classified along with Myxophyllum in the order Thigmotrichida. The proper classifications of Myxophyllum was hampered by the dramatic remodelling of its oral apparatus (reduction of the paroral membrane and adoral organelles, formation of vestibular kineties), a transformation that was likely induced by its firm association with terrestrial gastropods. The present study also documents that various ciliate lineages independently became commensals or parasites of various aquatic and terrestrial molluscs.

scholarly journals Scanning electron microscopy on Gotocotyla acanthura (Monogenea, Gotocotylidae) from Pomatomus saltatrix (Ostheichthyes, Pomatomidae) in Brazil

2011 ◽  
Vol 20 (4) ◽  
pp. 342-346 ◽  
Author(s):  
Maria Clara Pamplona-Basilio ◽  
Helene Santos Barbosa ◽  
Simone Chinicz Cohen
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Genital Atrium ◽  
Posterior Extremity ◽  
Dorsal Surface ◽  
Ventral Surface ◽  
The Body ◽  
Pomatomus Saltatrix ◽  
Muscular Structure ◽  
Scanning Electron

Gotocotyla acanthura (Parona & Perugia, 1896) Meserve, 1938 collected from the gills of Pomatomus saltatrix from the coast of the state of Rio de Janeiro state was analyzed using scanning electron microscopy (SEM). The study demonstrated the presence of a buccal cavity, a genital atrium on the ventral surface and a muscular structure on the dorsal surface at the level of the body constriction. An elongated haptor with 80 to 120 pedunculated clamps symmetrically distributed in two rows, with rib-like thickenings and a curved lappet bearing a pair of hooks at the posterior extremity of the body were also observed. The cirrus could be seen protruding from the genital atrium, armed with pectinate spines along its length and presenting up to eight pointed spines around the genital atrium.

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