Ambonychia

Classification
Phylum: Mollusca
Class: Bivalvia
Order: Pterioida
Family: Ambonychiidae
Genus: Ambonychia Hall, 1847
Cincinnatian Species: Ambonychia alata, Ambonychia radiata, Ambonychia robusta

Taxonomic Details

Synonyms: Byssonychia Ulrich 1893 (Subjectively by Vokes 1980);Eridonychia Ulrich 1895 (by Pojeta 1966)

Geologic Range
Middle Ordovician – Late Ordovician

Common Paleoecology
Ambonychia is an extinct genus of stationary epifaunal suspension feeders

Identification in Hand Sample:

  • Radial ornamentation is narrow plications
  • Prosocline to slightly opisthocline, orbicular to ovoid shells without anterior lobation
  • Valves ventricose, with byssal opening in the upper half of the anterior side, and marked by moderately strong radiating ribs.
  • Two or three slender lateral teeth and several cardinals are present
  • Muscular impressions large: one in each valve

Geographic Occurrences

Published Description

Eagle (1999)

  • Genus described from New Zealand specimens: Shell thin, equivalved, inequilateral, truncated anteriorly, convex; beak subacuminate, terminal or near-terminal, prosogyral; obliquity prosocline, acline, or opisthocline; with or without concentric growth striae, radial costae of varying number; byssal gape generally prominent, bilaterally symmetrical, located a short distance below the beaks, usually elliptical in outline; no anterior or posterior alation; decrease in shell convexity postero-dorsally.

Fossils of Ohio (1996):

  • Radial ornamentation is narrow plications
  • The genus Ambonychia, which ranges from Middle to Upper Ordovician, is represented in the Ordovician of Ohio by A. robusta Hall. This medium-sized species has narrow radial plications.

Pojeta, Jr. (1971):

  • However, the anterior of the shell remains rounded, and a specimen balanced on it is definitely unstable. A byssus would help stabilize the shell, but it seems unlikely that cyrtodontids of the Vanuxemia type were epifaunal after the fashion of Mytilus or Ambonychia.

Treatise on Invertebrate Paleontology, Part N, Mollusca 6 (1 of 3) (1969):

  • Prosocline to slightly opisthocline, orbicular to ovoid shells without anterior lobation; ornamented equally on both valves by simple radial costae; byssal gape generally prominent below beaks; dentition pseudoheterodont, composed of 2 or 3 small radial cardinal teeth in each valve below beaks and few posterior lateral elements located at posterior extremity of hinge margin.

McFarlan (1931):

  • (Under Byssonychia robusta)Equivalve, inequilateral, more or less winged posteriorly with beaks nearly or quite terminal. Valves ventricose, with byssal opening in the upper half of the anterior side, and marked by moderately strong radiating ribs. Two or three slender lateral teeth and several cardinals are present. Ligament external. Area striated.

Hall (1847):

  • Equivalve, inequilateral, compressed, alate or subalate posteriorly, obtuse and abruptly declining or curving downwards on the anterior margin. General form somewhat obliquely ovate, gibbous or inflated towards the umbones and on the center of the shell; cardinal margin very oblique, or approaching a line parallel to the direction of the umbones which are often incurved at the extremity, and equal, or project beyond, the line of the anterior extremity; surface marked by more or less prominent concentric striae, strong undulations, or fine radiating striae. Muscular impressions large: one in each valve.
  • The description includes several species of fossil shells, which, in some respects, vary in character, while, so far as regards general form and other prominent features, the evidently form a natural group.
  • This genus may be again subdivided, when we become better acquainted with the species which are presently arranged under it. Several of these species have heretofore been referred to Inoceramus, and Pterinea, which they bear some resemblances; but have a structure of the hinge different from the former, as well as being equivalve; while they differ from authentic specimens of the latter, in having no interior alation, which renders it desirable to distinguish these early forms by another name. It appears probable that Pterinea carinata of Goldfuss may be referred to the same genus, not being a true Pterinea according to the definition of that author.

A. alata


A. radiata


A. robusta