Pycnogonida

Austrodecus glaciale, copyright Claudia P. Arango.

Belongs within: Euarthropoda.
Contains: Ammotheidae.

The Pycnogonida, sea-spiders, are a group of highly distinctive marine arthropods with a tubular body bearing four to six pairs of walking legs. Feeding is via a tubular proboscis at the front of the cephalosoma, which also bears up to four pairs of appendages (the chelifores, palpi, ovigers and the first pair of walking legs) though the first three may each be absent. The upper Cambrian fossil larva Cambropycnogon klausmuelleri may represent the earliest record of Pycnogonida, sharing with crown-group sea-spiders the larval characters of massive chelicerae plus two post-cheliceral limbs not divided into podomeres, a weakly defined head shield, and mouth on a distinct forehead region (Waloszek & Dunlop 2002).

The Pantopoda is the clade containing crown-group sea-spiders. Members of this group have the trunk reduced to a single segment; other possible synapomorphies include the absence of excretory organs, the presence of gonopore openings on the second limb podomere, cement glands in the larval chelicerae, and egg-carrying by the males (Waloszek & Dunlop 2002).

<==Pycnogonida
    |  i. s.: Pentapantopus vogteliGD14
    |         Phoxichilus spinosusH64
    |         AmmothoaH64
    |           |--A. brevipes Hodge 1864H64
    |           `--A. longipes Hodge 1864H64
    |         Pasithoe vesiculosaH64
    |--Cambropycnogon Waloszek & Dunlop 2002WD02
    |    `--*C. klausmuelleri Waloszek & Dunlop 2002WD02
    `--Eupycnogonida [Palaeopycnogonida, Pantopoda, Podosomata]WD02
         |  i. s.: PalleneA99
         |           |--P. brevirostrisA99
         |           |--P. circularisH64
         |           `--P. pygmaea Hodge 1864H64
         |--Palaeoisopus Broili 1928SS04, B95 [Palaeoisopida, Palaeoisopodidae, Palaeoisopodina]
         |    `--P. problematicus Broili 1928WD02
         `--+--Flagellopantopus blockiLSE13, CVR07
            |--AustrodecidaeS94
            |    |--Pantopipetta Stock 1963S94
            |    |    |--P. bilobata Arnaud & Child 1988S94
            |    |    `--P. clavata Stock 1994S94
            |    `--Austrodecus Hodgson 1907SS04, S94
            |         |--A. glacialeSS04
            |         |--A. gordonaeSS04
            |         |--A. goughense Stock 1957S94
            |         |--A. stocki Child 1988S94
            |         `--A. tubiferum Stock 1957S94
            `--+--+--Palaeopantopus Broili 1928SS04, B95 [Palaeopantopoda, Palaeopantopodidae, Palaeopantopodina]
               |  |    `--P. maucheri Broili 1929WD02
               |  `--Haliestes Siveter, Sutton et al. 2004SS04
               |       `--*H. dasos Siveter, Sutton et al. 2004SS04
               `--+--AmmotheidaeS86
                  `--ColossendeidaeMG-H11
                       |--Hedgpethia calva Arango 2009MG-H11
                       |--Colossopantopus Charbonnier, Vannier & Riou 2007CVR07
                       |    `--*C. boissinensis Charbonnier, Vannier & Riou 2007CVR07
                       |--Rhopalorhynchus Wood-Mason 1873S94
                       |    |--R. filipes Stock 1991S94
                       |    |--R. sibogae Stock 1959MG-H11
                       |    `--R. tenuissimumSS04
                       `--Colossendeis Jarzynsky 1870RS10, S94
                            |--C. angusta Sars 1877 [incl. C. gracilis Hoek 1891]S94
                            |--C. colossea Wilson 1881MG-H11
                            |--C. macerrima Wilson 1881S94
                            |--C. megalonixGV09
                            |--C. melancholicus Stock 1975S86
                            |--C. minuta Hoek 1881S94
                            `--C. stramentiGV09

*Type species of generic name indicated

References

[A99] Ax, P. 1999. Das System der Metazoa II. Ein Lehrbuch der phylogenetischen Systematik. Gustav Fisher Verlag: Stuttgart (translated: 2000. Multicellular Animals: The phylogenetic system of the Metazoa vol. 2. Springer).

[B95] Bousfield, E. L. 1995. A contribution to the natural classification of Lower and Middle Cambrian arthropods: food-gathering and feeding mechanisms. Amphipacifica 2: 3–34.

[CVR07] Charbonnier, S., J. Vannier & B. Riou. 2007. New sea spiders from the Jurassic La Voulte-sur-Rhône Lagerstätte. Proceedings of the Royal Society of London Series B—Biological Sciences 274: 2685–2691.

[GD14] Garwood, R. J., & J. Dunlop. 2014. Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders. PeerJ 2: e641.

[GV09] Giribet, G., L. Vogt, A. Pérez González, P. Sharma & A. B. Kury. 2009. A multilocus approach to harvestman (Arachnida: Opiliones) phylogeny with emphasis on biogeography and the systematics of Laniatores. Cladistics 25: 1–30.

[H64] Hodge, G. 1864. List of the British Pycnogonoidea, with descriptions of several new species. Report of the British Association for the Advancement of Science 33 (Notices and Abstracts): 102–104.

[LSE13] Legg, D. A., M. D. Sutton & G. D. Edgecombe. 2013. Arthropod fossil data increase congruence of morphological and molecular phylogenies. Nature Communications 4: 2485.

[MG-H11] McEnnulty, F. R., K. L. Gowlett-Holmes, A. Williams, F. Althaus, J. Fromont, G. C. B. Poore, T. D. O’Hara, L. Marsh, P. Kott, S. Slack-Smith, P. Alderslade & M. V. Kitahara. 2011. The deepwater megabenthic invertebrates on the western continental margin of Australia (100–1100 m depths): composition, distribution and novelty. Records of the Western Australian Museum Supplement 80: 1–191.

[RS10] Regier, J. C., J. W. Shultz, A. Zwick, A. Hussey, B. Ball, R. Wetzer, J. W. Martin & C. W. Cunningham. 2010. Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences. Nature 463: 1079–1083.

[SS04] Siveter, D. J., M. D. Sutton, D. E. G. Briggs & D. J. Siveter. 2004. A Silurian sea spider. Nature 431: 978–980.

[S86] Stock, J. H. 1986. Pycnogonida (=Pantopoda). In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) pp. 698–700. E. J. Brill/Dr W. Backhuys: Leiden.

[S94] Stock, J. H. 1994. Indo-West Pacific Pycnogonida collected by some major oceanographic expeditions. Beaufortia 44 (3): 17–77.

[WD02] Waloszek, D., & J. A. Dunlop. 2002. A larval sea spider (Arthropoda: Pycnogonida) from the Upper Cambrian ‘Orsten’ of Sweden, and the phylogenetic position of pycnogonids. Palaeontology 45 (3): 421–446.

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