使用者:Lureplant/沙盒
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 復原圖
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| †Palaeoisopus problematicus Broili, 1928 |
古等足蛛 Palaeoisopus is a monotypic genus of fossil pycnogonid (sea spider), known only by one species, Palaeoisopus problematicus, discovered from the Lower Devonian Hunsrück Slate of Germany.[1] It have several characters unusual for a pycnogonid, such as swimming legs with alternating size, medially-arranged eyes, and most significantly, a long, segmented abdomen, which were highly reduced in modern counterparts.[1]
Morphology
編輯Palaeoisopus is a large sea spider, with a body length (excluding proboscis and chelifores) of at least 12.5 cm and leg spans of about 32 cm, comparable to those of a modern Colossendeis (giant sea spider).[1] The margins of each of its body parts were covered by tubercles, the cephalon (head section that bore eyes, proboscis, chelifores, palps, ovigers and 1st leg pair) and 3 trunk somites (section that bore the remaining leg pairs) are well-defined by ring-like segmentation. The abdomen apparently compose of 4 abdominal somites and a styliform telson,[2] but based on the medial position of anus (which, in telson-bearing chelicerates, always located at the ventral boundary of abdomen and telson), the latter was also suggest to be a fusion of 5th abdominal somite and the original telson.[1]
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Fossil of Palaeoisopus, showing the long, fully-extended 1st leg pair. -
Ventral fossil, showing full set of appendages. -
Fossil compose of 3 individuals, showing dorsal morphology.
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Medial to the anterodorsal margin of cephalon was an eye-bearing ocular tubercle. Unlike the paired 4-eyed arrangement of most pycnogonids, it compose of a pair of large eyes and 2 smaller eyes that arranged anteroposteriorly in a midline.[1] The anteriormost appendages were a pair of robust, pincer-like chelifores, which compose of 5 podomeres (3 for scape and 2 for pincer) instead of 3 or 4 (1 or 2 for scape and 2 for pincer) like those of the other pycnogonids.[3] Below the chelifores was a cylinderal proboscis that always tucked underneath the cephalon, making it almost invisible in dorsal view.[1] The palps and ovigers have similar morphology, the former terminated with a subchelate structures and the latter was apparently absent in some specimens, which may represent sexual dimorphism as seen in some modern pycnogonid taxa[1] such as Pycnogonidae and Phoxichilidiidae (female lacking ovigers).[4][5] Each of the leg base was surrounded by flexible, ring-like structure.[1] Among the 4 leg pairs the first one is significantly elongated, and its detail morphology slightly differ from the posterior counterparts as well (e.g. shorter basal segments, different setae arrangement, 4 flatten distal podomeres instead of 5).[1]
Paleoecology
編輯The large eyes, robust chelifores and oar-like legs suggest that Paleoisopus was a nektonic (swimming) visual predators, with associated stalked crinoid (sea lily) as a possible prey item.[1]
Phylogeny
編輯While some analysis placing Palaeoisopus within a derived position,[6] most studies suggest that Paleosiopus is a basal sea spider,[1][7][8] as the well-developed abdomen most likely represent a plesiomorphic condition of total-group Pycnogonida.[1][9]
References
編輯- ^ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Bergström, Jan; Stürmer, Wilhelm; Winter, Gerhard. Palaeoisopus, Palaeopantopus and Palaeothea, pycnogonid arthropods from the Lower Devonian Hunsrück Slate, West Germany. Paläontologische Zeitschrift. 1980-06-01, 54 (1–2): 7–54. S2CID 86746066. doi:10.1007/BF02985882 （英語）.
- ^ Dunlop, Jason A.; Lamsdell, James C. Segmentation and tagmosis in Chelicerata. Arthropod Structure & Development. 2017, 46 (3): 395–418. PMID 27240897. doi:10.1016/j.asd.2016.05.002 （英語）.
- ^ Brenneis, Georg; Arango, Claudia P. First description of epimorphic development in Antarctic Pallenopsidae (Arthropoda, Pycnogonida) with insights into the evolution of the four-articled sea spider cheliphore. Zoological Letters. December 2019, 5 (1): 4. PMC 6330760
. PMID 30656062. doi:10.1186/s40851-018-0118-7 （英語）.
- ^ Bain, Bonnie A.; Govedich, Fredric R. Courtship and mating behavior in the Pycnogonida (Chelicerata: Class Pycnogonida): a summary. Invertebrate Reproduction & Development. December 2004, 46 (1): 63–79. S2CID 84993360. doi:10.1080/07924259.2004.9652607 （英語）.
- ^ Ballesteros, Jesús A.; Setton, Emily V. W.; López, Carlos E. Santibáñez; Arango, Claudia P.; Brenneis, Georg; Brix, Saskia; Cano-Sánchez, Esperanza; Dandouch, Merai; Dilly, Geoffrey F.; Eleaume, Marc P.; Gainett, Guilherme. Phylogenomic resolution of sea spider diversification through integration of multiple data classes. bioRxiv. 2020-02-02, 38 (2): 686–701. PMC 7826184 . PMID 32915961. S2CID 213417127. doi:10.1101/2020.01.31.929612 （英語）.
- ^ Arango, Claudia P.; Wheeler, Ward C. Phylogeny of the sea spiders (Arthropoda, Pycnogonida) based on direct optimization of six loci and morphology. Cladistics. June 2007, 23 (3): 255–293. PMID 34905863. S2CID 84031914. doi:10.1111/j.1096-0031.2007.00143.x （英語）.
- ^ Siveter, Derek J.; Sutton, Mark D.; Briggs, Derek E. G.; Siveter, David J. A Silurian sea spider. Nature. October 2004, 431 (7011): 978–980. PMID 15496921. S2CID 4420863. doi:10.1038/nature02928 （英語）.
- ^ Poschmann, Markus; Dunlop, Jason A. A new sea spider (Arthropoda: Pycnogonida) with a flagelliform telson from the Lower Devonian Hunsrück Slate, Germany. Palaeontology. 2006, 49 (5): 983–989. doi:10.1111/j.1475-4983.2006.00583.x （英語）.
- ^ Kühl, Gabriele; Poschmann, Markus; Rust, Jes. A ten-legged sea spider (Arthropoda: Pycnogonida) from the Lower Devonian Hunsrück Slate (Germany). Geological Magazine. May 2013, 150 (3): 556–564. S2CID 129801458. doi:10.1017/S0016756812001033 （英語）.
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