Virtual Museum of Canada

Miguasha : From water to land (The Miguasha National Park)


Nicknamed "clam shrimps", conchostracans are a peculiar group of crustaceans.Asmusia membranaceamagnifying(68 kb) Looking vaguely like tiny shrimp, they have the distinct characteristic of living enclosed between two shells, little chitin valves 2 to 4 mm in diameter.

Described under the genera Estheria and Euestheria, the oldest conchostracan species are found in Lower Devonian rocks in Belgium and Germany. Closer to home, an as yet undescribed species of the same age is present in the Gaspé Sandstone of the Gaspé region.A conchostracanmagnifying(48 kb)

Conchostracans in the Escuminac Formation resemble the Lower Devonian specimens and have been assigned to the genus Asmusia. They are found by the thousands in the Escuminac Formation and it not unusual for their valves to partially cover some rock layers. Living freely in the water column, Asmusia membranacea were very abundant near the banks of the ancient Miguasha estuary. They seem to have been at the bottom of the food chain because they are often found in the abdomen of many fish species, as well as in coprolites of all sizes.

Euestheriamagnifying(88 kb)Conchostracans have survived until today without significant changes to their anatomy, and their little fossilized valves display few distinctive characteristics that distinguish genera. Present day conchostracans live in freshwater habitats and more rarely in brackish water, while those of the Devonian seem restricted to brackish environments in the transitional zone of continental marine environments. Fossilized conchostracans thus offer valuable clues about habitats for paleoenvironmental reconstructions.

Asmusia membranacea

Title: Asmusia membranacea
Author: Not available
Year: 1996

A specimen of the small conchostracan Asmusia membranacea, extracted from a coprolite in the Escuminac Formation.

A conchostracan

Title: A conchostracan
Author: Parc national de Miguasha
Sources: Parc national de Miguasha
Year: 2003

Conchostracans are small crustaceans protected by thin valves of chitin. These tiny creatures were a dietary staple for many fish in the ancient Miguasha estuary.


Title: Euestheria
Author: Parc national de Miguasha
Sources: Parc national de Miguasha
Year: 2005

A small conchostracan was also present during Lower Devonian time in the Gaspé. Assigned to the Eustheria genus, it is found with fish fauna and beds of plant fossils in the Battery Point Formation.