Gryphaea arcuata

Overview

Gryphaea arcuata is a bivalve with a strongly curved left valve and a right valve forming a low lid. Two different valves make up the outline of one body. This Early Jurassic organism has a distinctive side profile.^[1]

Key facts

The large left valve is convex and coiled, while the small right valve is flat or slightly concave. Differences in size and curvature create a clear contrast within one pair.^[1]

Time and place

J.43250, held in Oxford, is registered as Early Jurassic material from the Lower Lias of Gloucester in present-day Britain. The entire Jurassic spanned approximately 200–140 million years ago. The specimen record connects a name, locality, and age.^[2][3]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The umbo of the large left valve is strongly coiled, and the main valve is convex. The smaller right valve forms a low lid that is flat or slightly concave. The relationship between the curved region and low valve can be examined separately.^[1]

The shell of Gryphaea arcuata reveals growth traces as well as a curved form. A 7 cm long specimen at Warwickshire Museum preserves regular growth bands on its upper valve, providing clues to growth during life.^[9]

Habitat and reproduction

How similar are the two valves of a single bivalve? Gryphaea shows a clear difference between its large left valve and low right valve. Comparing them side by side reveals that different forms can join within one organism.^[1]

Fossil discovery

The museum registration of J.43250 connects the name Gryphaea arcuata with its occurrence at Gloucester in the Lower Lias. A 2025 preprint summarized the forms of both valves using earlier literature. Specimen records and morphological research contribute different information.^[2][1]

References

1. Lécuyer et al. (2025) — Pre-review manuscript on Gryphaea arcuata
2. Oxford University Museum of Natural History — Gryphaea specimen J.43250
3. International Commission on Stratigraphy (2024) — Geological time chart
4. Oxford University Museum of Natural History — Gryphaea specimen J.43250
5. International Commission on Stratigraphy (2024) — Geological time chart
6. Lécuyer et al. (2025) — Pre-review manuscript on Gryphaea arcuata
7. Ohmden study — Pentacrinites quenstedti
8. International Commission on Stratigraphy (2024) — Geological time chart
9. Radley (2009) — New information from museum invertebrate fossils

Research questions

How do a coiled umbo and a low lid form a pair? Examining the curvature and relative positions of the valves together helps explain their distinctive overall outline. This reads different left and right valves as one body.^[1]

Observation

Follow the strongly coiled left umbo along the convex valve. Then compare it with the low right lid to reveal the different outlines of the two valves.^[1]