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- Castellani, Christopher, et al.
(författare)
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First record of Cyanobacteria in Cambrian Orsten deposits of Sweden
- 2018
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Ingår i: Palaeontology. - : Wiley. - 0031-0239. ; 61:6, s. 855-880
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish Cambrian ‘Orsten’-type fossil sites have yielded diverse secondarily phosphatized three-dimensionally preserved microfossils, mainly of arthropod affinities. Similar material has also been recorded from Canada, the UK, Poland, Siberia, China and Australia. Only one other non-arthropod group, the Cycloneuralia, is commonly reported from any of these sites, leading to the general assumption that ‘Orsten’-type preservation is largely restricted to animals with a chitin-containing cuticle. We describe here secondarily phosphatized, originally unmineralized, thread-shaped fossils etched out of Cambrian ‘Orsten’-type deposits from the Agnostus pisiformis Biozone of the Alum Shale Formation in Sweden. These fossils strikingly resemble specimens previously described from Precambrian deposits, with at least two different morphotaxa identified (Siphonophycus kestron Schopf and Oscillatoriopsis longa Timofeev & Hermann) as well as the modern Oscillatoria. This leads us to interpret the new fossils as unbranched, uniseriate filamentous cyanobacteria. Our morphological investigations, combined with morphometrics, allow grouping the specimens assigned to O. longa into two size classes, suggesting an even higher diversity within the ‘Orsten’ assemblages. The lack of cyanobacterial material in any sample younger than the A. pisiformis Biozone indicates that rather drastic changes occurred in the environment, that is, substrate conditions on the Alum Shale seafloor. This coincided with a significant change in the composition of the trilobite communities and onset of the globally recognized Steptoean Positive Isotope Carbon Excursion (SPICE) in Scandinavia.
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| 3. |
- Nagler, Christina, et al.
(författare)
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Examination of functional morphology of dajiid isopods using Arthrophryxus sp. parasitising a mysid shrimp as an example
- 2020
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Ingår i: Acta Zoologica. - : Wiley. - 0001-7272 .- 1463-6395. ; 101:4, s. 339-352
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Tidskriftsartikel (refereegranskat)abstract
- Parasitic isopods have become specialised to many different host species and therefore show a wide variety of attachment and feeding specialisations. Often such structures are difficult to examine due to their small sizes which makes a more complete understanding of their functional morphology difficult. Here we present a new report and a first time high-resolution, non-SEM documentation of a parasitic epicaridean isopod, a female of the dajiid Arthrophryxus sp. from the Sea of Okhotsk. It was found during the SokhoBio 2015 on its host, a mysid shrimp (Holmsiella sp.). Arthrophryxus has only one formally described species, Arthrophryxus beringanus Richardson, 1908. With high-resolution documentation methods, we reveal new details of the morphological structures of mouthparts and thoracopods of this dajiid. Furthermore, we discuss the functional morphology of attachment to the host and feeding according to our new findings. We suggest that the thoracopods are involved in the attachment process even more than formerly assumed for different dajiids. The piercing-sucking mouthparts and the additional attachment mechanisms strongly indicate a permanent parasitism of the dajiid isopod. Permanent parasites affect the fitness of their hosts; therefore, deep-sea forms of dajiid isopods have direct impact on the deep-sea crustacean communities.
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| 4. |
- Stein, Martin, et al.
(författare)
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The stem crustacean Oelandocaris oelandica re-visited
- 2008
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Ingår i: Acta Palaeontologica Polonica. - 0567-7920 .- 1732-2421. ; 53:3, s. 461-484
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Tidskriftsartikel (refereegranskat)abstract
- The arthropod Oelandocaris oelandica from the upper Middle Cambrian “Orsten” of Sweden was recently recognized as a member of the early phase of crustacean evolution based on additional morphological detail from new specimens. Here we present a detailed investigation of all available material. It includes the description of a 400 μm long specimen probably representing an early developmental stage. Variation in size correlated with variation of trunk−segment numbers allowed recognition of different instars. The largest specimens do not exceed an estimated length of about 1 mm, indicating that our material may consist only of immature specimens. The characteristic, extremely long antennula of O. oelandica branches into three long rods. It may have served as the major structure to sweep in food, aided by the two subsequent appendages. These and the more posterior limbs were also responsible for locomotion. Minute pores on the outer edges of the posterior limbs and on the trunk tergites possibly contained sensilla originally, which may have served as water−current detectors. The presence of a minute proximal endite only on the third head appendage suggests a rather basal position of this species within Crustacea, because comparable developmental stages of other known stem crustaceans have such an endite on more of their appendages. Reconstruction of O. oelandica and its life attitudes (referred to the largest instar known) benefited from the application of 3D modelling. These helped, e.g., in identifying the combination of the plesiomorphic feeding function of the antennulae and the specialisation of the exopods of the next two appendages as a step toward the development of a sweep−net mode of feeding, one of the key novelties in the evolution of Crustacea. Such a mode of feeding coupled with locomotion of the three anterior appendages is still practiced in the naupliar and metanaupliar phases of many extant eucrustaceans, and even some adults.
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