Pycnogonida

Austrodecus glaciale, copyright Claudia P. Arango.

Belongs within: Cheliceriformes.
Contains: Pantopoda.

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).

<==Pycnogonida
    |--Cambropycnogon Waloszek & Dunlop 2002 WD02
    |    `--*C. klausmuelleri Waloszek & Dunlop 2002 WD02
    `--Eupycnogonida [Palaeopycnogonida] WD02
         |--Palaeoisopus Broili 1928 SS04, B95 [Palaeoisopida, Palaeoisopodina]
         |    `--P. problematicus Broili 1928 WD02
         `--+--Austrodecus SS04
            |    |--A. glaciale SS04
            |    `--A. gordonae SS04
            |--Flagellopantopus blocki LSE13, CVR07
            `--+--Pantopoda SS04
               `--+--Palaeopantopus Broili 1928 SS04, B95 [Palaeopantopoda, Palaeopantopodina]
                  |    `--P. maucheri Broili 1929 WD02
                  `--Haliestes Siveter, Sutton et al. 2004 SS04
                       `--*H. dasos Siveter, Sutton et al. 2004 SS04

*Type species of generic name indicated

REFERENCES

[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.

[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): 1–7.

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

[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.