Belongs within: Rhynchonellata.
Contains: Koninckinidae, Retzioidea, Athyrisinidae, Meristellinae, Athyrididae, Meristidae.
The Athyridida are a lineage of largely smooth, impunctate brachiopods known from the Upper Ordovician to the Jurassic (Boucot et al. 1965).
Characters (Boucot et al. 1965): Smooth or pauciplicate, impunctate, with narrow hinge line; pedicle-valve interarea obsolete or lacking; beak commonly truncated by circular foramen. Spiralia directed laterally or ventrally; crura project parallel to median plane; primary lamellae invariably united by more or less elaborate jugum; accessory lamellae arising from jugum commonly present.
<==Athyridida [Athyrididina, Rostrospiracea]
| i. s.: PachyplaxWBM97
| |--P. elongataWBM97
| `--P. gyraleaWBM97
| Kellerella Nikitin et al. 1996HC04
| `--K. ditissimaHC04
| Nikolaispira rasilisHC04
| Weibeia Fu 1982HC04
|--KoninckinidinaWCB00
| |--KoninckinidaeHB93
| `--Cadomella Oehlert in Fischer 1887M-WW65 [Cadomellacea, Cadomellidae, Cadomellinae, CadomelloideaHB93]
| |--*C. moorei (Davidson 1876)M-WW65, HB93 [=Leptaena mooreiM-WW65]
| `--C. davidsoni (Eudes Deslongchamps 1854)HB93
|--RetziidinaWCB00
| |--RetzioideaBJ65
| |--MongolospiroideaWCB00
| |--AthyrisinoideaHB93
| | |--AthyrisinidaeBJ65
| | `--MetathryrisinidaeHB93
| | |--Metathyrisina merita Rong & Yang 1981HB93
| | `--Molongia Mitchell 1921HB93, BJ65
| | `--*M. elegans Mitchell 1921BJ65
| `--Rhynchospirinidae [Rhynchospirinae, Rhynchospirinoidea]WCB00
| |--HomoeospirellaHB93
| |--Homoeospira Hall & Clarke 1893BJ65
| | `--*H. evax (Hall 1863) [=Rhynchospira evax]BJ65
| `--Rhynchospirina Schuchert & LeVene 1929 [=Rhynchospira Hall 1859 non Ehrenberg 1845, Rhyncospira (l. c.)]BJ65
| |--*R. formosa (Hall 1857) [=Waldheimia formosa, *Rhynchospira formosa]BJ65
| |--R. haidingeri Barrande 1879HB93
| `--R. maxwelliBJ65
`--AthyrididinaWCB00
|--Retziella Nikiforova 1937BJ65 [RetzielloideaWCB00]
| `--*R. weberi Nikiforova 1937BJ65
|--Nucleospiridae [Nucleospiroidea]WCB00
| |--Amphitomella Bittner 1890HB93, BJ65
| | `--*A. hemisphaeroidica (Klipstein 1843) [=Terebratula hemisphaeroidica]BJ65
| `--Nucleospira Hall 1859MM02
| |--*N. ventricosa (Hall 1857) [=Spirifer ventricosa]MM02
| |--N. carlukensisWBM97
| |--N. cunctata Cooper & Grant 1976HB93
| |--N. pisiformis Hall 1859HB93
| |--N. pisum (Sowerby 1839) [=Spirifer pisum]MM02
| `--N. robustaMM02
|--Meristellidae [Meristelloidea]WCB00
| |--MeristellinaeBJ65
| `--HindellinaeBJ65
| |--Hindella Davidson 1882BJ65
| | `--*H. umbonata (Billings 1862) [=Athyris umbonata]BJ65
| |--Whitfieldella Hall & Clarke 1893BJ65
| | |--*W. nitida (Hall 1843) [=Atrypa nitida]BJ65
| | `--W. upsilonBJ65
| `--Hyattidina Schuchert 1913 [=Hyattella Hall & Clarke 1893 non Lendenfeld 1889]BJ65
| |--*H. congesta (Conrad 1842) [=Atrypa congesta, *Hyattella congesta]BJ65
| |--H. junea (Billings 1866)M03
| |--H. remota Modzalevskaya 2003M03
| `--H. sulcata Williams 1962HB93
`--Athyridoidea [Athyracea, Athyridacea]BJ65
|--AthyrididaeCSZ03
|--Xenosaria [Xenosariidae]HB93
| `--X. exotica Cooper & Grant 1976HB93
|--Diplospirellidae [Diplospirellinae, Diplospirinae]HB93
| |--Sprigerellina pygmaea Dagis 1974HB93
| |--Oxycolpella oxycolps (Emmrich 1855)HB93
| |--Diplospirella Bittner 1890BJ65
| | `--*D. wissmanni (Münster 1841) [=Terebratula wissmanni]BJ65
| |--Anisactinella Bittner 1890BJ65
| | `--*A. quadriplecta (Münster 1841) [=Terebratula quadriplecta]BJ65
| |--Euractinella Bittner 1890BJ65
| | `--*E. contraplecta (Münster 1841) [=Terebratula constraplecta]BJ65
| `--Pexidella Bittner 1890BJ65
| `--*P. strohmayeri [=Spirifer strohmayeri]BJ65
`--MeristidaeSM04