Superfamily Discinoidea (Early Ordovician-Recent)
The Discinids are a small long-lived group of inarticulate brachiopods with chitinophosphatic shells. Both valves are rounded, with a convex, cap-shaped discoid to conical brachial valve, and a flat pedicle valve. The pedicle opening is a deep narrow notch indenting the posterior margin of the pedicle valve, or an enclosed narrow slit located behind the apex. Although the shell substance is dominantly chitinophosphatic, some genera have external calcareous shell laminae.
Orbiculoidea, showing attachment when alive. The pedicle valve is nearly completely flat, and circular in outline. the pedicle issues from a slit located between the centrally placed apex and margin of the valve.
The Discinida are variously included under the Acrotretida in the Treatise), or with the Lingulida in the Linguliformes (the EuroBrach arrangement), or (as followed here) in both.
|Trematis millipunctata Hall
time: Sandbian, (Late Ordovician-) place: Laurentia (North America) habitat: shallow water benthos
size: shell about 1.2 cm in diameter
note the pedicle slit
In the Treatise these are included under the Acrotretida
page uploaded 7 June 2002
(originally uploaded on Kheper site uploaded 11 May 1999)
page by M. Alan Kazlev (Creative Commons Attribution license) 1999-2002