Sous-embranchement (subphylum) des Rhynchonelliformea  
Classe des Rhynchonellata 
Ordre des Terebratulida 

Sous-ordre des Terebratulidina 
Super-famille des Terebratuloidae 
Super-famille des Dyscolioidae 
Super-famille des Cancellothyroidea 

Genus Zygonaria Cooper, 1983
[Type species = Gryphus joloensis Dall, 1920, p. 313]

Small to medium, rounded oval; rectimarginate; beak short, erect; foramen medium, mesothyrid; pedicle collar well developed, teeth large; cardinal process large, semicircular; loop anteriorly rounded and narrowed.


Diagnosis from volume 5 of the
Treatise on Invertebrate Paleontology (2002)

Extant Species of Zygonaria
  • Z. joloensis (Dall, 1920)
  • Z. davidsoni (Adams, 1867)
  • Diagnosis

    Zygonaria joloensis   (Dall, 1920)

    Type locality: Jolo Light, off Jolo, Philippines, at 582 m (st. 512: 06°03'15"N, 120°35'30"E)
    Depth range: 192 - 582 m

    Gryphus joloensis Dall, 1920

    Original Diagnosis - Dall (1920, p. 313)

    Shell rounded triangular, widest at the anterior third, smooth except for concentric lines of giowth, not folded; beak high, incurved and conspicuous with a large entire foramen, the deltidial plates small and narrow, coalescent; hinge margin thickened, longer than the short stout teeth, anterior margin smooth, muscular impressions obscure; brachial valve less inflated, dental plates wide, the sockets faintly cross striated, the loop short, rather wide, the lower portion with a median deep sulcus behind and a corresponding projection in front, the crura short and blunt; the plates are separated to the apex where there is a prominent callosity serving as cardinal process ; the front edge of the valves is nearly straight.

    This species is considered by Cooper (1983) as type species, but according to the ICZN priority the correct species should be T. davidsoni Adams.

    Zygonaria davidsoni  (Adams, 1867)

    Type locality: Satanomosaki, Japan, at 100 m.
    Depth range: 101 - 188 m

    Terebratula davidsoni Adams, 1867, p. 314.
    Liothyris vitrea, var. davidsoni Adams: Davidson, 1886, p. 9, Pl. 1: 14-16.

    Original Diagnosis - Adams (1867, p. 314)

    T. testa ovato-globosa, lævi, albida, laminis incrementi distinctis, irregularibus, ad basin validioribus ; margine ventrali circulari ; rostro producto, recurvato ; foramine parvo, perfecto ; deltidio parvo, concavo ; apophysi simplici, 1/3 longitudinis testæ superante.