Reconstruction of Medfrazyga clauticae (Palaeozygopleuridae, late Early Devonian) from Frýda & Blodgett (2004).

Falls within: Ptenoglossa.

The Loxonematoidea is a superfamily of gastropods with extremely tall, narrow spires. Gastropods ranging in age from the Silurian to the present day (the deep-sea families Provannidae and Abyssochrysidae) have been assigned to the Loxonematoidea by various authors. However, the Silurian and Devonian loxonematoids of the families Loxonematidae and Palaeozygopleuridae differ in their protoconch morphology from later taxa and it has been suggested that the later families are not closely related to the true loxonematoids but are convergent forms. The phylogenetic position of the Loxonematoidea is similarly debatable: features of the more recent families suggest relationships with the Caenogastropoda, but the simple protoconch of the earlier 'true' loxonematoids may indicate a more basal position outside the caenogastropod-heterobranch-neritimorph clade (Frýda & Blodgett 2004).

The Loxonematidae are mostly relatively large gastropods known from the Middle Ordovician to Lower Carboniferous, with a median sinus in the labrum and mostly collabral ornamentation. The Palaeozygopleuridae are smaller gastropods from the Devonian and Lower Carboniferous, with the labral sinus shallow or absent (Knight et al. 1960).

Characteristics (from Frýda & Blodgett 2004, for Loxonematidae and Palaeozygopleuridae only): Slender, high-spired shells. Large protoconch with less than one whorl, lacking a true larval shell.

Loxonematoidea [Stylogastropoda]
    |  i. s.: Spiromphalus PE02
    |         Nodoloxonema Blodgett, Frýda & Racheboeuf 1999 FB04
    |           `--*N. plusquelleci Blodgett, Frýda & Racheboeuf 1999 FB04
    |--Spirostylus Kittl 1894 [Spirostylidae, Spirostylinidae] TE01
    |    |--*S. subcolumnaris (Münster 1841) [=Melania subcolumnaris] TE01
    |    `--S. linctus (Böhm 1895) [=Omphaloptycha lincta; incl. O. porrecta Böhm 1895] TE01
    |--Polygyrina Koken 1892 KC60 [Polygyrinidae BR05]
    |    |--*P. lommelii (Münster 1841) [=Turritella lommelii] KC60
    |    |--P. depressa Wang in Wang & Xi 1980 NE02
    |    |--P. gracilior (Schauroth 1855) NE02
    |    |--P. sichuanensis Pan 1982 NE02
    |    `--P. venusta Yu & Wang in Wang & Xi 1980 NE02
    |--Palaeozygopleuridae [Palaeozygopleurinae] BR05
    |    |--Pragozyga Frýda 1999 FB04
    |    |    `--*P. costata Frýda 1999 FB04
    |    |--Medfrazyga Frýda & Blodgett 2004 FB04
    |    |    `--*M. clauticae Frýda & Blodgett 2004 FB04
    |    |--Devonozyga Horny 1955 KC60
    |    |    `--*D. perneri Horny 1955 KC60
    |    `--Palaeozygopleura Horný 1955 BR05
    |         |  i. s.: P. chlupaci Frýda 1993 FB04
    |         |--*P. (Palaeozygopleura) alinae (Perner 1907) [=Zygopleura alinae] FB04
    |         |--P. (Bohemozyga Frýda & Bandel 1997) FB04
    |         |--P. (Bojozyga Horný 1955) FB04
    |         |--P. (Palaeozyga Horný 1955) FB04
    |         |    `--P. (*P.) bohemica FB04
    |         `--P. (Rhenozyga Frýda 2000) FB04
    |              |--P. (*R.) retrostriatum (Kirchner 1915) [=Loxonema retrostriatum] FB04
    |              |--P. (R.) machenryi Cook 1997 FB04
    |              `--P. (R.) reifenstuhli Frýda & Blodgett 2004 FB04
    `--Loxonematidae [Loxonematinae, Omospiridae, Omospirinae] BR05
         |--Holopella M’Coy 1851 [Holopellidae] BR05
         |--Katoptychia Perner 1907 FB04 [=Cataptychia Cossmann 1909 KC60]
         |    `--*K. alba Perner 1907 KC60
         |--Stylonema Perner 1907 FB04
         |    `--*S. potens (Perner 1907) [=Loxonema (*Stylonema) potens] KC60
         |--Omospira Ulrich in Ulrich & Scofield 1897 BR05
         |    `--*O. laticincta Ulrich in Ulrich & Scofield 1897 KC60
         |--Hypselentoma Weller 1929 KC60
         |    `--*H. perhumerosa (Meek 1872) [=Pleurotomaria perhumerosa] KC60
         |--Sisenna Koken 1896 KC60
         |    `--*S. turbinata (Hörnes 1855) [=Pleurotomaria turbinata] KC60
         |--Girvania Longstaff 1924 KC60
         |    `--*G. excavata Longstaff 1924 KC60
         |--Spiroecus Longstaff 1924 KC60
         |    `--*S. girvanensis Longstaff 1924 KC60
         |--Aulacostrepsis Perner 1907 KC60
         |    `--*A. simplex Perner 1907 KC60
         `--Loxonema Phillips 1841 BR05 [incl. Rhabdostropha Donald 1905 KC60]
              |--*L. sinuosum (Sowerby 1839) [=Terebra sinuosa] KC60
              |--L. anglicum F71
              |--L. babbindoonensis Etheridge 1907 F71
              `--L. lamellosum F71

*Type species of generic name indicated


[BR05] Bouchet, P., J.-P. Rocroi, J. Frýda, B. Hausdorf, W. Ponder, Á. Valdés & A. Warén. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1-2): 1-397.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1-167.

[FB04] Frýda, J., & R. B. Blodgett. 2004. New Emsian (Late Early Devonian) gastropods from Limestone Mountain, Medfra B-4 quadrangle, west-central Alaska (Farewell Terrane), and their paleobiogeographic affinities and evolutionary significance. Journal of Paleontology 78 (1): 111-132.

[KC60] Knight, J. B., L. R. Cox, A. M. Keen, R. L. Batten, E. L. Yochelson & R. Robertson. 1960. Gastropoda: systematic descriptions. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—General Features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—General Features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia, pp. I169-I331. Geological Society of America, and University of Kansas Press.

[NE01] Nützel, A. & D. H. Erwin. 2002. Battenizyga, a new Early Triassic gastropod genus with a discussion of the caenogastropod evolution at the Permian/Triassic boundary. Paläontologische Zeitschrift 76 (1): 21-27.

[PE02] Pan, H.-Z., & D. H. Erwin. 2002. Gastropods from the Permian of Guangxi and Yunnan Provinces, south China. Journal of Paleontology 76 (Memoir 56): 1-49.

[TE01] Tong, J., & D. H. Erwin. 2001. Triassic gastropods of the southern Qinling Mountains, China. Smithsonian Contributions to Paleobiology 92: 1-47.

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