Palaeoisopus is a monotypicgenus of fossilpycnogonid (sea spider), known only by one species, Palaeoisopus problematicus, discovered from the Lower DevonianHunsrück 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]
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]
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.
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]
Paleoecologyedit
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]
Phylogenyedit
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]
Referencesedit
^ abcdefghijklBergström, Jan; Stürmer, Wilhelm; Winter, Gerhard (1980-06-01). "Palaeoisopus, Palaeopantopus and Palaeothea, pycnogonid arthropods from the Lower Devonian Hunsrück Slate, West Germany". Paläontologische Zeitschrift. 54 (1–2): 7–54. doi:10.1007/BF02985882. S2CID 86746066.
^Dunlop, Jason A.; Lamsdell, James C. (2017). "Segmentation and tagmosis in Chelicerata". Arthropod Structure & Development. 46 (3): 395–418. doi:10.1016/j.asd.2016.05.002. PMID 27240897.
^Brenneis, Georg; Arango, Claudia P. (December 2019). "First description of epimorphic development in Antarctic Pallenopsidae (Arthropoda, Pycnogonida) with insights into the evolution of the four-articled sea spider cheliphore". Zoological Letters. 5 (1): 4. doi:10.1186/s40851-018-0118-7. PMC6330760. PMID 30656062.
^Bain, Bonnie A.; Govedich, Fredric R. (December 2004). "Courtship and mating behavior in the Pycnogonida (Chelicerata: Class Pycnogonida): a summary". Invertebrate Reproduction & Development. 46 (1): 63–79. doi:10.1080/07924259.2004.9652607. S2CID 84993360.
^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 (2020-02-02). "Phylogenomic resolution of sea spider diversification through integration of multiple data classes". bioRxiv. 38 (2): 686–701. doi:10.1101/2020.01.31.929612. PMC7826184. PMID 32915961. S2CID 213417127.
^Arango, Claudia P.; Wheeler, Ward C. (June 2007). "Phylogeny of the sea spiders (Arthropoda, Pycnogonida) based on direct optimization of six loci and morphology". Cladistics. 23 (3): 255–293. doi:10.1111/j.1096-0031.2007.00143.x. PMID 34905863. S2CID 84031914.
^Siveter, Derek J.; Sutton, Mark D.; Briggs, Derek E. G.; Siveter, David J. (October 2004). "A Silurian sea spider". Nature. 431 (7011): 978–980. doi:10.1038/nature02928. PMID 15496921. S2CID 4420863.
^Poschmann, Markus; Dunlop, Jason A. (2006). "A new sea spider (Arthropoda: Pycnogonida) with a flagelliform telson from the Lower Devonian Hunsrück Slate, Germany". Palaeontology. 49 (5): 983–989. doi:10.1111/j.1475-4983.2006.00583.x.
^Kühl, Gabriele; Poschmann, Markus; Rust, Jes (May 2013). "A ten-legged sea spider (Arthropoda: Pycnogonida) from the Lower Devonian Hunsrück Slate (Germany)". Geological Magazine. 150 (3): 556–564. doi:10.1017/S0016756812001033. S2CID 129801458.
January 01, 1970
palaeoisopus, monotypic, genus, fossil, pycnogonid, spider, known, only, species, problematicus, discovered, from, lower, devonian, hunsrück, slate, germany, have, several, characters, unusual, pycnogonid, such, swimming, legs, with, alternating, size, mediall. Palaeoisopus is a monotypic genus of fossil pycnogonid sea spider known only by one species Palaeoisopus problematicus discovered from the Lower Devonian Hunsruck 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 PalaeoisopusTemporal range Lower Devonian PreꞒ Ꞓ O S D C P T J K Pg N Fossil Reconstruction Scientific classification Kingdom Animalia Phylum Arthropoda Subphylum Chelicerata Class Pycnogonida Order Palaeoisopoda Family PalaeoisopodidaeDubinin 1957 Genus PalaeoisopusBroili 1928 Species P problematicus Binomial name Palaeoisopus problematicusBroili 1928 Contents 1 Morphology 2 Paleoecology 3 Phylogeny 4 ReferencesMorphology editPalaeoisopus 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 nbsp Fossil of Palaeoisopus showing the long fully extended 1st leg pair nbsp Ventral fossil showing full set of appendages nbsp Fossil compose of 3 individuals showing dorsal morphology 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 editThe 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 editWhile 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 edit a b c d e f g h i j k l Bergstrom Jan Sturmer Wilhelm Winter Gerhard 1980 06 01 Palaeoisopus Palaeopantopus and Palaeothea pycnogonid arthropods from the Lower Devonian Hunsruck Slate West Germany Palaontologische Zeitschrift 54 1 2 7 54 doi 10 1007 BF02985882 S2CID 86746066 Dunlop Jason A Lamsdell James C 2017 Segmentation and tagmosis in Chelicerata Arthropod Structure amp Development 46 3 395 418 doi 10 1016 j asd 2016 05 002 PMID 27240897 Brenneis Georg Arango Claudia P December 2019 First description of epimorphic development in Antarctic Pallenopsidae Arthropoda Pycnogonida with insights into the evolution of the four articled sea spider cheliphore Zoological Letters 5 1 4 doi 10 1186 s40851 018 0118 7 PMC 6330760 PMID 30656062 Bain Bonnie A Govedich Fredric R December 2004 Courtship and mating behavior in the Pycnogonida Chelicerata Class Pycnogonida a summary Invertebrate Reproduction amp Development 46 1 63 79 doi 10 1080 07924259 2004 9652607 S2CID 84993360 Ballesteros Jesus A Setton Emily V W Lopez Carlos E Santibanez Arango Claudia P Brenneis Georg Brix Saskia Cano Sanchez Esperanza Dandouch Merai Dilly Geoffrey F Eleaume Marc P Gainett Guilherme 2020 02 02 Phylogenomic resolution of sea spider diversification through integration of multiple data classes bioRxiv 38 2 686 701 doi 10 1101 2020 01 31 929612 PMC 7826184 PMID 32915961 S2CID 213417127 Arango Claudia P Wheeler Ward C June 2007 Phylogeny of the sea spiders Arthropoda Pycnogonida based on direct optimization of six loci and morphology Cladistics 23 3 255 293 doi 10 1111 j 1096 0031 2007 00143 x PMID 34905863 S2CID 84031914 Siveter Derek J Sutton Mark D Briggs Derek E G Siveter David J October 2004 A Silurian sea spider Nature 431 7011 978 980 doi 10 1038 nature02928 PMID 15496921 S2CID 4420863 Poschmann Markus Dunlop Jason A 2006 A new sea spider Arthropoda Pycnogonida with a flagelliform telson from the Lower Devonian Hunsruck Slate Germany Palaeontology 49 5 983 989 doi 10 1111 j 1475 4983 2006 00583 x Kuhl Gabriele Poschmann Markus Rust Jes May 2013 A ten legged sea spider Arthropoda Pycnogonida from the Lower Devonian Hunsruck Slate Germany Geological Magazine 150 3 556 564 doi 10 1017 S0016756812001033 S2CID 129801458 Retrieved from https en wikipedia org w index php title Palaeoisopus amp oldid 1188379184, wikipedia, wiki, book, books, library,
