Xenusiid

Xenusiids Temporal range: Early Cambrian to Carboniferous PreЄ Є O S D C P T J K Pg N
File:Hallucigenia sparsa.JPG
Hallucigenia sparsa
Scientific classification
Kingdom:	Animalia
Superphylum:	Ecdysozoa
Phylum:	†"Lobopodia"
Class:	†Xenusia Dzik & Krumbiegel, 1989
Orders
See text.

Class Xenusia, the Xenusiids, represents the subset of lobopodian worms that fall in the stem-lineage of Onychophora. Their type genus is Xenusion. They have relatively large, annulated, cylindrical body. Their lobopod legs have tubercles at their bases. Some have large frontal appendages, although these may represent taphonomic artefacts. Their mouth is terminal or subterminal, and they are marine. They probably represent a grade (paraphyletic group) rather than a clade (monophyletic group).

Systematics

Xenusia includes the following orders and families:

Order Archonychophora

• Archonychophora Hou & Bergstrom, 1995 – undifferentiated appendages; each segment the same as each other.
  • Luolishaniidae Hou & Bergstrom, 1995 – three small rounded sclerites per segment – these are thorn-shaped spines.
    • Luolishania Hou & Chen 1989
    • Miraluolishania Liu & Shu 2004
  • Paucipodiidae Hou et al., 2004 – with no dorsal sclerites, two claws, fine annulation and few segments.
    • Paucipodia Hou et al. 2004

These taxa are only known from the Chengjiang (Cambrian Stage 2 Series 3).

Order Protonychophora

• Protonychophora Hutchinson, 1930 – spiny legs, reduced tail.
  • Aysheaiidae Walcott, 1911 – many claws on each leg. Anterior grasping appendages with long spines.
    • Aysheaia Walcott 1911
  • Xenusiidae Dzik & Krumbiegel, 1989 – >20 leg-bearing segments; paired, rounded sclerites on each segment; spiny legs.
    • Xenusion Pompeckj, 1927
    • Jianshanopodia Liu et al – from Chengjiang; two rows of tubercles but no obvious sclerites.
    • Hadranax Budd & Peel 1998 – from the Sirius Passet. Lacks obvious dorsal armature, but bears four 'nodes' per row.

Order Scleronychophora

• Scleronychophora Hou & Bergstrom, 1995 – paired sclerites; elongated head sclerites.
  • Eoconchariidae Hou & Shu, 1987 – ~10 leg-bearing segments, small head, sieve-like sclerites, varying in shape along body; curved claws on annulated legs; terminal mouth and anus.
    • Microdictyon Bengtson et al
    • Quadratapora Hao and Shu, 1987
    • Fusuconcharium Hao and Shu, 1987
  • Hallucigeniidae Conway Morris, 1977 – ~10 leg-bearing segments; large sclerites covering head; sclerites on each segment are long spines.
    • Hallucigenia Conway Morris 1977 – from the Chengjiang, Kaili and Burgess Shale.
  • Cardiodictyidae Hou & Bergstrom, 1995 – many segments (~23); large sclerites cover head; hexagonal sclerite on each body segment.
    • Cardiodictyon Hou et al 1991 – known from the Chengjiang.

Order Paronychophora

• Paronychophora Hou & Bergstrom, 1995 – short, downwards facing head; papillae on body and legs, some arranged in rows; shield-like sclerites on head; dorsal armature of spines; claw-like jaws; annulated legs [Note: diagnosis modified in ].
  • Onychodictyidae Hou & Bergstrom, 1995
    • Onychodictyon Hou et al 1991

Order unassigned

• Orstenotubulus Maas et al 2007 – from the Furongian Orsten deposits – with retractable dorsal spines.
• Carbotubulus Haug et al 2012 – from the Mazon creek. Dorwal armature uncertain. Few segments, long limbs.
• Mureropodia from the Stage 2 Murero lagerstatten, Spain.

'Phylum' Onychophora

Onychophora are distinguished by their terrestrial habit, their ventral mouth; their antennae, jaws and oral papillae; they seem to be most closely related to the Paronychophora. Their first fossils are Carboniferous (Helenodora), although they may have had a cryptic earlier history.