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Argyrotheca

   
   

Sous-embranchement (subphylum) des Rhynchonelliformea
Classe des Rhynchonellata
Ordre des Terebratulida
Sous-Ordre des Terebratellidina
Super-famille des Megathyridoidea
Famille des Megathyrididae

 
 

 
 
 
 


Genus Argyrotheca Dall, 1900
 

[Type-species = Terebratula cuneata Risso, 1826, p. 388 ]

Small, com- monly transversely ovate with wide hinge line but outline variable; ventribiconvex, smooth to more commonly multiplicate; beak short, subtruncate; foramen large, commonly hypothyrid; deltidial plates narrow. Pedicle collar well developed, sup- ported by long, narrow, median septum. Cardinal process short, transversely elongate, buttressed by long, high, thick median septum; crura widely separate, short, prominent, pointed; loop long, formed of 2 slender, arcuate descending branches attached to base of crura, valve floor, and anterior end of median septum; short septal flanges present in adult stages; lophophore large, schizolophous, spicules not observed.

Upper Cretaceous (Maastrichtian) - Present

Diagnosis from volume 5 of the
Treatise on Invertebrate Paleontology

Occurrences: cosmopolitan.


Species of Argyrotheca
  • A. cuneata (Risso, 1826) - see photography below
  • A. cordata (Risso, 1826) - since 2008 considered as type-species of Joania
  • A. cistellula (Searles-Wood, 1841)
  • A. barrettiana (Davidson, 1866)
  • A. schrammi (Crosse & Fischer, 1866)
  • A. woodwardiana (Davidson, 1866)
  • A. lutea (Dall, 1871)
  • A. rubrotincta (Dall, 1871)
  • A. australis (Blochmann, 1910)
  • A. bermudana Dall, 1911
  • A. mayi Blochmann, 1914 - perhaps belonging to Joania
  • A. johnsoni Cooper, 1934
  • A. lowei Hertlein & Grant, 1944
  • A. jacksoni Cooper, 1973
  • A. somaliensis Cooper, 1973
  • A. thurmanni Cooper, 1973
  • A. crassa Cooper, 1977
  • A. hewatti Cooper, 1977
  • A. rubrocostata Cooper, 1977
  • A. grandicostata Logan, 1983
  • A. arguata Grant, 1983 - perhaps belonging to Joania
  • A. angulata Zezina, 1987
  • A. neocaledonensis  Bitner, 2010
  • A. furtiva Simon, 2010
  • A. cooperi Bitner et Logan, 2013

  • Only fossil species:

    • A. costulata (Seguenza, 1866)
    • A. dertomutinensis Sacco, 1902: Tortonian
    • A. dertotaurinensis Sacco, 1902: Tortonian
    • A. subcordata Boetger
    • A. sabaratensis Pajaud & Tambareau, 1970: Sparnacian
    • A. alavensis Pajaud & Plaziat, 1972
    • A. anomala Cooper, 1983: Late Eocene - perhaps belonging to Joania
    • A. laevis Cooper, 1988: Tertiary
    • A. macneili 
    • A. quadrata 
    • A. quadrata transversa 
    • A. semicostata 
    • A. ageriana Taddei Ruggiero, 1993: Pleistocene
    • to be completed
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    Argyrothec cuneata   (Risso, 1826)

     

    Argyrotheca cuneata: in about 15 m depth at Tarrafal, northwestern coast of Sao Tiago Island (Cape Verde Islands). Copyright © Peter Wirtz - identification by Alan Logan.

    Diagnosis from Risso (1826)

    T. Testa glabra, rotundata, superne truncata; valvis ambabus costis latis, depressis, divaricantibus, longitudinaliter striatis sculptis; lateribus rotundatis ; epidermide lutescente, radiis ruberrimis.
    Coq. lisse, arrondie, tronquée au sommet; à valves sculptées de larges côtes déprimées, divergentes, striées longitudinalement; à côtés arrondis; l'épiderme est jaunâtre, avec les rayons d'un rouge vif. Long. 0,003. Séj. Régions coralligènes. App. Toute l'année.


    Argyrotheca cuneata

    Argyrotheca jacksoni Cooper, 1973

    Type locality: a reef cave at Ras Muhammad, S Sinai peninsula, 10 m.
    Depth range: 5 - 90 m et 284-286 m

    Argyrotheca jacksoni Cooper, 1973 p. 17.
    Argyrotheca australis: Zezina (1987)
    Argyrotheca sp.: Hiller (1994).

    Diagnosis from Cooper (1973)


    Small yellow-gray Argyrotheca, with rectangular dorsal valves with about 11 costae.

    Argyrotheca somaliensis   Cooper, 1977

    Type locality: Anton Bruun Cruise 9, station 447, 10°00'N, 51°15'E, 59-61 m.
    Depth range: 55 - 145 m

     

    Diagnosis from Cooper (1977)


    Small coarsely costate Argyrotheca, rectangular in outline with well-formed delthyrium and scalloped anterior margin.

    Argyrotheca cooperi   Bitner et Logan, 2013

    Type locality: Suakin Archipelago, Sudan, 18° 57’N, 38° 15’E, at 90m.
    Depth range: 90 - 669 m

    Diagnosis from Bitner & Logan (2013)


    Small Argyrotheca with a wide hinge line and 4-6 heavy rounded ribs, producing scalloped anterior margin.

    Argyrotheca angulata  Zezina, 1987

    Type locality: St. BENT.06DR, Benthedi cruise, off Glorieuses Is., France (Mozambique Channel), depth 500-460 m.
    Depth range: 90 - 669 m

    Diagnosis from Zezina (1987)

    Shell : small, white, widely transverse (length of pedicle valve 2.1 mm, length of brachial valve 1.6 mm, width of shell 3.3 mm). Shell surface : almost smooth, but faintly faceted with two feeble ridges on each half of the valve ventrally and dorsally, middle ridges beeing moved aside (the middle ridges are stronger than the lateral ones). Tall area : inclined 45° to the plane of the shell, striated transversly. Deltidial plates : narrow, triangular, stretched out along the sides of rectangular hypothyrid open foramen which does not reach the umbo of pedicle valve. Pedicle collar: horizontal, flat and wide, grown together with the septum in its posterior half. Pedicle : short and flat, its attaching surface forming a brush of short filaments. No crura; descending branches of brachial loop attached posteriorly to the front of socket ridges and anteriorly to the back surface of pyramid-shaped septum; posterior part of the septum near the umbo forms a cavity for a brood pouch.
    Lophophore : schizolophous.


    Argyrotheca furtiva   Simon, 2010

    Type locality: shipwreck "Mutiara", Bay of Palu, off Donggala Harbour, Sulawesi, Indonesia, at 30m.
    Depth range: about 30 m

    Diagnosis from Simon (2010)

    Small, thick, ventribiconvex shell, subpentagonal in outline with obtuse wing-like lateral extremities, lenticular in lateral profile. Four radial incipient costae on either valve in opposite folding. Shell surface regularly tuberculate under SEM examination. Rectimarginate anterior commissure and sinuous lateral commissure. Large pedicle collar not buttressed by the low blade-like ventral septum, which extends for two-thirds of the valve length. Obtusely pointed crural processes. Weakly defined descending branches fused up to the mid-valve with valve floor and raised on the lateral slopes and the posterior part ofthe dorsal septum. Dorsal septum rather low, narrowly subtriangular in lateral profile with anterior slope straight, not serrate nor tuberculate. Strong adductor muscles scars developed in the posterior part of the dorsal valve with one large ptmcta present on either internal side of these scars.