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Platygena
Classification
Phylum:
Mollusca
Class:
None
Subclass:
Pteriomorphia
Order:
Pterioida
Suborder:
Ostreina (oysters)
Superfamily:
Ostreacea
Family:
Ostreidae
Subfamily:
Ostreinae - Incubatory genera
Formal Genus Name and Reference:
Platygena ROMANOVSKIY, 1882, p. 46-47, 58-60
Type Species:
Ostrea asiatica ROMANOVSKIY, 1879, p. 150, M
Images
(Click to enlarge in a new window)
Fig. J120,1. *P. asiatica (ROMANOVSKIV), USSR; 1a-e, LV ext., int., RV int., part of ext., both valves post. view, XO.48 (Romanovskiy, 1882).
Synonyms
Platigena
Geographic Distribution
C. Asia-USSR-Afr. (Sudan-Libya)
Age Range
Beginning Stage in Treatise Usage:
Up.Eoc.(Rishtan.)
Beginning International Stage:
Priabonian
Fraction Up In Beginning Stage:
0
Beginning Date:
37.71
Ending Stage in Treatise Usage:
Up.Eoc.(Rishtan.)
Ending International Stage:
Priabonian
Fraction Up In Ending Stage:
100
Ending Date:
33.9
Description
Medium-sized to large and f1attish, width about 0.16 to 0.25 of height; outline roughly orbicular; old shells higher than long. LV gently convex, RV even less convex. Outline of valve cavity in LV banjo-shaped (resembling guitar-shaped valve cavity of Sokolowia) , with slender subparallel-sided dorsal neck and suborbicular ventral banjo body. Space on either side of banjo neck filled out with former temporary anterodorsal and posterodorsal valve margins left behind during growth of shell. Later growth restricted to continued gradual shift of shell cavity in ventral direction without increase in size of cavity, which in LV is very shallow, without umbonal cavity or overhang at hinge plate. Adductor muscle imprint reniform, ,its longer axis tilted, nearly central in location. No chomata. Numerous growth squamae, many of which are frilled in harmony with nearly continuous small radial ribs. [Playgena is similar to Deltoideum, from which it differs in central location of the reniform muscle imprint. The genera evidently are only superficially similar. Platygena resembles Sokolowia, but differs in its flatness. lack of shell twists, and in being not at all a Gryphaea homeomorph. Its very shallow shell cavity proves that it never had a large gonad lodged within it. Therefore, it must have been an incubatory oyster that produced few eggs. Closeness to Ostrea is proved by its reniform muscle imprint.]
References
Museum or Author Information
Classification
Phylum:
Mollusca
Class:
None
Subclass:
Pteriomorphia
Order:
Pterioida
Suborder:
Ostreina (oysters)
Superfamily:
Ostreacea
Family:
Ostreidae
Subfamily:
Ostreinae - Incubatory genera
Formal Genus Name and Reference:
Platygena ROMANOVSKIY, 1882, p. 46-47, 58-60
Type Species:
Ostrea asiatica ROMANOVSKIY, 1879, p. 150, M
Images
(Click to enlarge in a new window)
Fig. J120,1. *P. asiatica (ROMANOVSKIV), USSR; 1a-e, LV ext., int., RV int., part of ext., both valves post. view, XO.48 (Romanovskiy, 1882).
Synonyms
Platigena
Geographic Distribution
C. Asia-USSR-Afr. (Sudan-Libya)
Age Range
Beginning Stage in Treatise Usage:
Up.Eoc.(Rishtan.)
Beginning International Stage:
Priabonian
Fraction Up In Beginning Stage:
0
Beginning Date:
37.71
Ending Stage in Treatise Usage:
Up.Eoc.(Rishtan.)
Ending International Stage:
Priabonian
Fraction Up In Ending Stage:
100
Ending Date:
33.9
Description
Medium-sized to large and f1attish, width about 0.16 to 0.25 of height; outline roughly orbicular; old shells higher than long. LV gently convex, RV even less convex. Outline of valve cavity in LV banjo-shaped (resembling guitar-shaped valve cavity of Sokolowia) , with slender subparallel-sided dorsal neck and suborbicular ventral banjo body. Space on either side of banjo neck filled out with former temporary anterodorsal and posterodorsal valve margins left behind during growth of shell. Later growth restricted to continued gradual shift of shell cavity in ventral direction without increase in size of cavity, which in LV is very shallow, without umbonal cavity or overhang at hinge plate. Adductor muscle imprint reniform, ,its longer axis tilted, nearly central in location. No chomata. Numerous growth squamae, many of which are frilled in harmony with nearly continuous small radial ribs. [Playgena is similar to Deltoideum, from which it differs in central location of the reniform muscle imprint. The genera evidently are only superficially similar. Platygena resembles Sokolowia, but differs in its flatness. lack of shell twists, and in being not at all a Gryphaea homeomorph. Its very shallow shell cavity proves that it never had a large gonad lodged within it. Therefore, it must have been an incubatory oyster that produced few eggs. Closeness to Ostrea is proved by its reniform muscle imprint.]