Priapozoa

Selkirkia columbia, from Smith et al. (2015).

Belongs within: Cycloneuralia.
Contains: Priapulida.

Worm buttons
Published 22 January 2008
Palaeoscolecid dermal sclerite, from here.

The Palaeoscolecida were actually known as entire animals long before their dermal armation was described. However, confusion resulted when said armation was described as isolated problematic fossils before a connection was made between the animal and its armour (Ivantsov & Wrona, 2004). The photo above shows one of the isolated sclerites, originally described under the name Hadimopanella. Palaeoscolecid sclerites are round and button-like, with a central array of nodules that vary in different species from low and rounded to higher and pointed. Opinions on the nature of these microfossils (to appreciate how small they are, the scale bar on the photo above represents 0.03 mm) varied from some sort of dermal armour to the remains of reproductive cysts (Repetski, 1981). The dermal armour theory, of course, won out when the connection was made between the isolated sclerites and ornamentation on the compressed body fossils almost simultaneously by different authors in 1989 (Ivantsov & Wrona, 2004).

Tabelliscolex hexagonus, from Han et al. (2007).

Palaeoscolecidans were a successful group of burrowing worms in the early Palaeozoic, when they were probably even more significant than the annelids. Originally interpreted as annelids, their segmented appearance is apparently only superficial and results from alternating bands of larger and smaller plates (Ivantsov & Wrona, 2004). Well-preserved specimens from the Chengjiang Fauna possess an anterior spiny proboscis like that of the modern priapulids, and palaeoscolecidans have most often been regarded as priapozoans*. Other authors have suggested relationships with the modern nematomorphs, or as stem-panarthropods (Han et al., 2007). At the very least, a position within the Ecdysozoa, the clade uniting these three groups, seems well-established.

*Bring on the nomenclatorial quibble. Most authors supporting this affinity have simply referred to palaeoscolecidans as “priapulids”. The modern priapulids are a small, well-defined group of worms, while the various Palaeozoic taxa regarded as stem-priapulids show a much higher diversity of body plans (many of them, for instance, were far more elongate than any living priapulid, while no living priapulid possesses a dermal armour like that of palaeoscolecidans). Personally, I’d prefer to only refer to the crown group as priapulids, and use the name Priapozoa to cover the larger group including the stem forms.

Systematics of Priapozoa
<==Priapozoa [Ottoidae, Ottoiidae]C-S98
    |--LoriciferaDD04
    |    |--SiriloricaEL11
    |    |--Pliciloricus enigmaticusMS98
    |    `--Nanaloricus Kristensen 1983 [Nanaloricidae]K86
    |         |--*N. mysticus Kristensen 1983K86
    |         `--N. khaitatus Todaro & Kristensen 1998TK98
    `--+--PriapulidaOH17
       `--+--Selkirkia Walcott 1911DD04, H62 [Selkirkiidae]
          |    |--*S. major (Walcott 1908)H62 (see below for synonymy)
          |    |--S. columbia Conway Morris 1977SHB15
          |    |--S. elongata Luo & Hu 1999SHB15
          |    |--S. spencei Resser 1939SHB15
          |    `--S. willoughby Conway Morris & Robison 1988SHB15
          `--+--+--Ottoia Walcott 1911DD04, H62
             |  |    |--*O. prolifica Walcott 1911H62
             |  |    `--O. tricuspida Smith, Harvey & Butterfield 2015SHB15
             |  `--+--Scolecofurca rara Conway Morris 1977DD04, SHB15
             |     `--Miskoiidae [Miskoidae]W93b
             |          |--Miskoia Walcott 1911H62
             |          |    `--*M. preciosa Walcott 1911H62
             |          `--Louisella Walcott 1911DD04, H62
             |               `--*L. pedunculata Walcott 1911H62
             `--+--Maotianshania cylindrica Sun & Hou 1987DD04, SHB15
                `--+--Cricosomia jinningensis Hou & Sun 1988DD04, W93b
                   `--Palaeoscolecidae [Palaeoscolecida]H62
                        |--Palaeoscoleca sinensis Hou & Sun 1988W93a
                        |--HadimopanellaD94
                        |    |--H. knappologica (Bengtson 1977)D94
                        |    `--H. silurica Wang 1990WS93
                        `--Palaeoscolex Whittard 1953DD04, H62
                             |--*P. piscatorum Whittard 1953H62
                             |--P. ratcliffei Robison 1969H75
                             `--P. ruedmanni Roy & Croneis 1931W93a
Priapozoa incertae sedis:
  MilaculumSHC01
  ‘Ceratophyton’ dumufuntumSHB15
  ‘Ceratophyton’ spinuconumSHB15
  Acosmia maotiania Chen & Zhou 1997SHB15
  Eopriapulites sphinx Liu et al. 2014SHB15
  Eximipriapulus globocaudatus Ma et al. 2014SHB15
  Laojieella thecata Han et al. 2006SHB15
  Omnidens amplus Hou et al. 2006SHB15
  Paraselkirkia sinica (Luo & Hu 1999) [=Selkirkia sinica; incl. P. jinningensis Huo et al. 1999]SHB15
  Paratubiluchus bicaudatus Han et al. 2004SHB15
  Sicyophorus rara Luo & Hu 1999 [=Protopriapulites haikouensis Hou et al. 1999]SHB15
  Xiaoheiqingella peculiaris [incl. Yunnanpriapulus halteroformis Huang et al. 2004]SHB15
  Lagenula striolata Luo & Hu 1999 (n. d.)SHB15
  Oligonodus specialis Luo & Hu 1999 (n. d.)SHB15
  Sandaokania latinodosa Luo & Hu 1999 (n. d.)SHB15
  Lecythioscopa simplex Walcott 1931W93b
Nomen nudum: Ottoia inopinata Conway Morris 1977SHB15

*Selkirkia major (Walcott 1908)H62 [=Orthotheca majorH62, Cambrorhytium majorSHB15; incl. Selkirkia gracilis Walcott 1911SHB15]

*Type species of generic name indicated

References

[C-S98] Cavalier-Smith, T. 1998. A revised six-kingdom system of life. Biological Reviews 73: 203–266.

[DD04] Dong, X-P., P. C. J. Donoghue, H. Cheng & J.-B. Liu. 2004. Fossil embryos from the Middle and Late Cambrian period of Hunan, south China. Nature 427: 237–240.

[D94] Dzik, J. 1994. Evolution of ‘small shelly fossils’ assemblages of the early Paleozoic. Acta Palaeontologica Polonica 39 (3): 247–313.

[EL11] Erwin, D. H., M. Laflamme, S. M. Tweedt, E. A. Sperling, D. Pisani & K. J. Peterson. 2011. The Cambrian conundrum: early divergence and later ecological success in the early history of animals. Science 334: 1091–1097.

Han, J., J. Liu, Z. Zhang, X. Zhang & D. Shu. 2007. Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China. Acta Palaeontologica Polonica 52 (2): 423–431.

[H75] Häntzschel, W. 1975. Treatise on Invertebrate Paleontology pt W. Miscellanea Suppl. 1. Trace Fossils and Problematica 2nd ed. The Geological Society of America: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[H62] Howell, B. F. 1962. Worms. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt W. Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica pp. W144–W177. Geological Society of America, and University of Kansas Press.

Ivantsov, A. Y., & R. Wrona. 2004. Articulated palaeoscolecid sclerite arrays from the Lower Cambrian of eastern Siberia. Acta Geologica Polonica 54 (1): 1–22.

[K86] Kristensen, R. M. 1986. Loricifera. In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) pp. 119–121. E. J. Brill/Dr W. Backhuys: Leiden.

[MS98] Margulis, L., & K. V. Schwartz. 1998. Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth 3rd ed. W. H. Freeman and Company: New York.

[OH17] Ou, Q., J. Han, Z. Zhang, D. Shu, G. Sun & G. Mayer. 2017. Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity. Proceedings of the National Academy of Sciences of the USA 114 (33): 8835–8840.

Repetski, J. E. 1981. An Ordovician occurrence of Utahphospha Müller & Miller. Journal of Paleontology 55 (2): 395–400.

[SHB15] Smith, M. R., T. H. P. Harvey & N. J. Butterfield. 2015. The macro- and microfossil record of the Cambrian priapulid Ottoia. Palaeontology 58 (4): 705–721.

[SHC01] Sutton, M. D., L E. Holmer & L Cherns. 2001. Small problematic phosphatic sclerites from the Ordovician of Iapetus. Journal of Paleontology 75 (1): 1–8.

[TK98] Todaro, M. A., & R. M. Kristensen. 1998. A new species and first report of the genus Nanaloricus (Loricifera, Nanaloricida, Nanaloricidae) from the Mediterranean Sea. Italian Journal of Zoology 65: 219–226.

[W93a] Wills, M. A. 1993a. Annelida. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 271–278. Chapman & Hall: London.

[W93b] Wills, M. A. 1993b. Miscellania. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 555–560. Chapman & Hall: London.

[WS93] Wills, M. A., & J. J. Sepkoski Jr. 1993. Problematica. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 543–554. Chapman & Hall: London.

Leave a comment

Your email address will not be published. Required fields are marked *