Editing Naraoiidae

{{Short description|Family of arthropods (fossil)}}
{{Automatic taxobox
| name = Naraoiidae
| image = Naraoia_spinosa.jpg
| image_caption = ''Naraoia spinosa''
| fossil_range = {{fossilrange|526|416}}[[Atdabanian|Late Atdabanian]]-[[Silurian|Pridoli]]
| taxon = Naraoiidae
| authority = [[Charles Doolittle Walcott|Walcott]], 1912
| subdivision_ranks = Genera
| subdivision =
* ''[[Misszhouia]]''
* ''[[Naraoia]]''
*?''[[Pseudonaraoia]]''<ref name="BUDIL">{{cite journal|last=Budil |first=Peter |author2=Oldřich Fatka |author3=Jana Brutansová|title=Trilobite fauna of the Šárka Formation at Praha – Červený vrch Hill (Ordovician, Barrandian area, Czech Republic)|journal=Bulletin of Geosciences|year=2003|volume=78|issue= 2|pages=113–117|url=http://www.geology.cz/bulletin/fulltext/05-budil.pdf}}</ref>
}}

'''Naraoiidae''' is a [[family (biology)|family]], of extinct, soft-shelled [[trilobite]]-like [[arthropod]]s, that belongs to the [[order (biology)|order]] [[Nektaspida]]. Species included in the Naraoiidae are known from the second half of the [[Lower Cambrian]] to the end of the [[Silurian|Upper Silurian]]. The total number of collection sites is limited and distributed over a vast period of time: [[Maotianshan Shale]] and [[Balang Formation]] (China), [[Burgess Shale]] and Bertie Formation (Canada), the Šárka Formation (Czech Republic),<ref name="BUDIL" /> [[Emu Bay Shale]] (Australia), Idaho and Utah (USA). This is probably due to the rare occurrence of the right circumstances for [[Burgess Shale type preservation#Preservational regime|soft tissue preservation]], needed for these non-calcified [[exoskeletons]].

== Ecology ==
Naraoiids probably were [[deposit feeder]]s (''Naraoia'' and ''[[Pseudonaraoia]]''), [[predator]]s or [[scavenger]]s (''Misszhouia''), living on the sea floor.

== Description ==
[[File:Naraoia compacta fossil.jpg|left|thumb|Fossils of ''[[Naraoia|Naraoia compacta]]'']]
The species of the family ''Naraoiidae'' are almost flat (dorso-ventrally). The upper (or dorsal) side of the body consists of a non-calcified transversely oval or semi-circular headshield ([[Cephalon (arthropod head)|cephalon]]), and a circular to long oval tailshield ([[Trilobite#Pygidium|pygidium]]) equal to or longer than the cephalon, without any body segments in between. The body is narrowed at the articulation between cephalon and pygidium. The antennas are long and many-segmented. There are no eyes. The 17 to 25 pairs of legs have two branches on a common basis, like trilobites. The outer (dorsal) branches of the limbs (exopods) have flattened side branches (setae) on the shaft (probably acting as [[gills]]). The inner branches (or endopods are composed of 6 or 7 segments (or podomeres).<ref name="Chen">Chen, J.-Y., G.D. Edgecombe and L. Ramskjöld (1997). Morphological and ecological disparity in naraoiids (Arthropoda) from the Early Cambrian Chengjiang Fauna, China. Records of the Australian Museum 49(1), pp. 1–24.[http://australianmuseum.net.au/Uploads/Journals/17838/249_complete.pdf]</ref>

=== Differences with other Nectaspida ===
Naraoiidae lack thoracic segments (or tergites), while the species of the sister family [[Liwiidae]] have between 3 and 6 tergites.

== Taxonomic history ==
The taxonomic placement of the Naraoiidae has long been debated until detailed appendages were uncovered, that showed that ''N. compacta'' shares biramous legs of very comparable anatomy with [[Trilobita|trilobites]]. Some debate is still going on if the parent [[taxon]] ''Nektaspida'' should be included in the Trilobita, or is better placed as a sister group.<ref>{{cite book |author=E. Bonino & C. Kier |year=2010 |title=The Back to the Past Museum Guide to Trilobites}}</ref>

== Key to the genera ==
{|
|- valign="top"  align="left"
! scope="row" width="3%" | '''1''' 
| width="97%" | Pygidium less than {{frac|1|1|2}}× as long (along the axis) as the cephalon; If the digestive system is visual, gut more than {{frac|1|8}} of the width of the body, with branched diverticula filling most of the cephalon; Antennas implanted laterally. Margin of cephalon and/or pygidium spined or entire. 17 to 19 pairs of biramous legs.<ref name="Ramskold">L. Ramskold, J.-Y. Chen, G.D.  Edgecombe, and G.-Q. Zhou ( 1996). Preservational folds simulating tergite junctions in tegopeltid and naraoiid arthropods. Lethaia 29:15-20.
{{ISSN|0024-1164}}.[http://www.nhm.ac.uk/resources-rx/files/ramskold-et-al-1996-preservational-folds-94162.pdf]</ref> → '''''[[Naraoia]]'''''
|- valign="top" align="left"
! scope="row" width="3%" | '''-''' 
| width="97%" | Pygidium more than {{frac|1|3|4}}× as long as the cephalon; If the digestive system is visual, gut less than {{frac|1|8}} of the width of the body, with four pairs of small bifurcating sacs of equal size reaching at most {{frac|1|3}} of the width of the cephalon; Antennas implanted anteriorly. Margins of cephalon and pygidium entire. 25 pairs of biramous legs. Up to 6&nbsp;cm in length.<ref name="Ramskold" /><br />→ '''''[[Misszhouia| Misszhouia longicaudata]]''''' (Zhang & Hou 1985), jr. syn. ''Naraoia longicaudata''
|}

== References ==
{{Reflist}}

== External links ==
* [http://www.trilobites.info/naraoia.htm Are Naraoids trilobites?] Photographs of specimens and discussion of classification controversy

{{Artiopoda}}
{{Taxonbar|from=Q150727}}

[[Category:Nektaspida]]
[[Category:Terreneuvian first appearances]]
[[Category:Silurian extinctions]]
[[Category:Prehistoric arthropod families]]