Early Cambrian – Early Carboniferous (Tournaisian)
Craniopsidae is an extinct family of stationary epifaunal suspension feeders
Description of the Family
- Shell is calcareous in composition, impunctate, biconvex, elliptical to linguloid in outline, with strong concentric ornamentation
- Internal muscle scars situated posterolaterally, strongly developed
- Lacks any indication of a pedicle
- Smooth limbus present in both valves
Treatise on Invertebrate Paleontology, Part H (2) (2000) Same as the order:
- Shell biconvex, elongate oval to subcircular; visceral area of both valves extending anterior to midvalve; scars of dorsal oblique internal muscles situated posterolaterally; cemented at apical region of ventral valve, or free lying; shell calcitic, impunctate.
- Simple morphology and taxa within the order can be defined only on characters such as the presence or absence of pseudointerareas, visceral platforms, median ridges, position of the umbo, and presence of attachement scar (cicatrix). The shell is usually equally biconvex, with the umbo situated marginally or posteriorly. Only some craniopsids have well-developed pseudointerareas.
Harper et al. (1993):
- “Shell biconvex, elongate oval to subcircular; visceral area of both valves extending anterior to midvalve; scars of dorsal oblique internal muscles situated posterolaterally; cemented at apical region of ventral valve, or free lying; shell calcitic, impunctate.”
- “The craniopside muscle system is here modeled after that of the Craniida ; however, alternative reconstructions, based mainly on the pattern of muscles present in lingulides, have also been proposed. MERGL (1986), for example, suggested that the unpaired posteromedian scar might correspond to the lingulide umbonal muscle, but with the view adopted here it corresponds to the unpaired median muscle (levator and protrusor ani) of craniides (Fig. 90). According to MERGL, the remaining three paired dorsal and four ventral muscle scars can be correlated with the lingulide transmedian, anterior lateral, middle lateral, and central muscle scars; but the transmedian and central scars are also comparable with the craniide anterior and posterior adductors; the dorsal middle lateral scars may correspond to the craniide internal oblique muscles that were attached to the anterior part of the ventral median ridge. The ventral anterior lateral scars may have represented the oblique lateral muscles that were attached to the anterior body wall, while the dorsal anterior lateral may be similar to the brachial protractor muscles of craniides.”
- Shell calcareous, impunctate, biconvex, elliptical to linguloid in outline, with strong concentric ornament, which may be lamellose, growth holoperipheral or mixoperipheral. Apparently lacking a pedicle, attached by cementation or free. Central muscle scars strongly developed, usually on low solid platform. Smooth limbus present in both valves.