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

Sous-ordre des Terebratulidina 
Super-famille des Dyscolioidae 

Genus Dyscolia Fischer & Œlhlert, 1890
[Type species = Terebratulina wyvillei Davidson, 1878 (p. 436)]

Medium to very large, subtrigonal to elongate oval; ventribiconvex; surface smooth or with fine, zigzag capillae; beak short, suberect, often truncated or labiate; foramen large, epithyrid to submesothyrid; symphytium almost concealed; pedicle collar long, anteriorly excavated; cardinal process not developed, diductor muscles attached to apical pit; outer hinge plates very weakly developed; crural processes weak, blunt; loop small (less than 0.3 dorsal valve length), thin, with rounded, anterolateral extremities; lophophore small, modified schizolophe; spicules very abundant; four main mantle canals in each valve, branching pattern pinnate.

Pliocene - Present

Diagnosis from volume 5 of the
Treatise on Invertebrate Paleontology (2006)

Extant Species of Dyscolia
  • D. wyvillei (Davidson, 1878)
  • D. subquadrata (Jeffreys, 1878)
  • D. johannisdavisi (Alcock, 1894)
  • D. radiata Cooper, 1981
  • D. sp
  • Diagnosis

    D. wyvillei   (Davidson, 1878)

    Type locality: "dredged off Culebra Island, to the north-west of St. Thomas, in the West Indies, at a depth of 390 rathoms".
    Depth range: 73 - 1922 m.

    Terebratulina wyvilli Davidson, 1878, p. 436

    Diagnosis (Álvarez & Emig, 2005)

    Concha de tamaño grande (L máx. = 55 mm, A máx. = 45 mm), blanquecina, biconvexa a ventribiconvexa, subpentagonal, superficie externa con capilas radiales finas y líneas de crecimiento concéntricas regulares (A-F). Gancho ventral corto (A, C). Interior de la valva dorsal con un braquidio sencillo, corto, terebratuliforme (G, H); proceso cardinal poco desarrollado al que se le fija la terminación dorsal de los músculos diductores (G). Margen lateral interno de ambas valvas con pequeños tubérculos (G, H). Canales del manto ampliamente ramificados anterolateralmente (G, H).


    Facsimile of the Fig. 41 of Álvarez & Emig (2005). Views : A-dorsal ; B-ventral ; C-lateral ; D-anterior; E-postero-dorsal; F-posterior; G-H-open shell.
    Click on to enlarge

    Dyscolia radiata   Cooper, 1981

    Type locality: st. MD.08: 6, DC 47: 33°11.4'S, 44°00.4'E, Walters Bank, at 620-635 m.
    Depth range: 263 - 635 m.

    Diagnosis (Cooper, 1981)

    Subtriangular, loop narrow, crural processes obtuse, surface covered by fine irregular capillae.

    Copper (1981, p. 24) states: “Dyscolia? radiata most resembles Dyscolia ewingi Cooper from off South America in south Atlantic waters. There is also resemblance to Liothyrella? neozelanica.”

    Dyscolia sp.

    References and Depth: Foster (1974): 915-1153 m, 1887-1894 m; Foster (1989): 4118 m; Hiller (1994): 680-715; Zezina (1980): 580 m.

    See Antarctic - sub-Antarctic map

    Dyscolia johannisdavisi (Alcock, 1894)

    Type locality: "dredged in the Laccadive-Maldive basin, off the island Uliganu of the Northern Maldive atoll, at a depth of 719 fathoms, on a bottom of fine coral sand".
    Depth range: 735 - 1463 m.

    Terebratula johannis-davisi Alcock, 1894

    Diagnosis (Alcock, 1894)

    Shell pyriform, inequilateral, thin but strong, its surface smooth except for the concentric lines of growth, and microscopically punctate : in colour purple-brown. The shell is remarkable in being inequilateral, having a well-marked bulge to the left side (the shell being held ventral valve downwards and beak pointing backwards) : and this asymmetry is shown by the lines of growth to have existed from an early period of life.
    The dorsal valve is slightly more convex than the ventral ; and both valves have the margin simple, entire, and broadly turned over and bevelled all round.
    Internally, the dorsal valve has very prominent cardinal processes, and a small slender loop, the greatest convexity of which does not reach forward beyond the first fifth of the length of the shell.
    The ventral valve has a re-curved beak which conceals the small deltidium, the latter consisting of a single piece transversely striated, and the beak being truncated by a thick-edged foramen.

    Dyscolia subquadrata  (Jeffreys, 1878)

    Type locality: "Off the coast of Portugal, in 500-600 fathoms".
    Depth range: 117 - 4700 m.

    Terebratula subquadrata Jeffreys, 1878, p. 402.

    Diagnosis (Álvarez & Emig, 2005)

    Concha generalmente gruesa de tamaño, medio a grande, blanca, amarillenta o marrón claro, subtrigonal, biconvexa a ventribiconvexa. Superficie externa con líneas de crecimiento concéntricas, regulares, y una ornamentación radial fina, no siempre bien desarrollada (A, J, K). Gancho ventral corto, foramen grande, epitírido a submesotírido (A, B, D, E). Interior de la valva ventral con dientes en forma de gancho y pequeños (B); huellas musculares poco marcadas (B). Interior de la valva dorsal con un braquidio sencillo, que ocupa aproximadamente 1/3 de la longitud de la valva dorsal y 1/4 de su anchura (C, F, B).


    Facsimile of the Fig. 60 of Álvarez & Emig (2005). Views : A-dorsal ; B-internal ventral ; C-F-H-internal dorsal ; D-dorsal; E-postero-dorsal; G-anterior; I-lateral; J-K-details.
    Click on to enlarge