Jurassic

virgula

Jurassic

Phylum: Mollusca
Class: Bivalvia
Order: Ostreoida
Family: Gryphaeidae

Growth lines
Ribs
Umbo
Two valves

Mineral replacement of shell

A feature characteristic of the Gryphaeidae is two asymmetric valves. The upper valve (the right valve in development) is flat, whilst the lower (left) valve is curved.

Gryphaea dilatata

Jurassic

Phylum: Mollusca
Class: Bivalvia
Order: Ostreoida
Family: Gryphaeidae

Umbo
Growth lines
Two articulated valves

Mineral replacement of shell

Asymmetric valves distinctive for Gryphaeidae - flat upper (right) valve and curved lower (left) valve. With this shape Gryphaea reclined in the sediment, filter feeding.

Repair scars are visible on most Gryphaea specimens. When the animal was attacked unsuccessfully by a predator, a small amount of a growth line at the edge of the shell would have been chipped away. The next growth line would have filled in the missing part of the shell, leaving an uneven growth line pattern, with a 'v' or 'u' shape visible.

Triassic to Cretaceous

Phylum: Mollusca
Class: Bivalvia
Order: Ostreoida
Family: Bakevelliidae
Genus: Gervillella

Umbo
Growth lines
Two articulated valves

Mineral replacement of shell

Judging by the long elongate valves, this bivalve likely lived as a stationary semi-infaunal suspension feeder.

Cretaceous

Triassic to present

Phylum: Mollusca
Class: Bivalvia
Order: Pectinoida
Family: Spondylidae
Genus: Spondylus

Umbo
Ribs
Dorso-ventral symmetry
Two valves

Mineral replacement of shell

Rarely for bivalves Spondylus articulates its valves using a ball and socket hinge, not a toothed hinge. It was spiny when alive (to discourage predators).

Jurassic to Cretaceous

Phylum: Mollusca
Class: Bivalvia
Order: Praecardioida
Family: Inoceramidae
Genus: Inoceramus

Ribs
Umbo
Two valves
Near dorso-ventral symmetry

Internal mould

Eocene

Phylum: Mollusca
Class: Bivalvia
Order: Carditoida
Family: Crassatellidae
Genus: Crassatella

Ribs
Growth lines
Umbo
Dentition
Adductor muscle scars
Palial line

Original shell material

Crassatella lived as a mobile infaunal suspension feeder. It could change location as a response to predators, food supply or other factors.

Lithophaga inclusa

Jurassic

Lithophaga: Triassic to recent

Phylum: Mollusca
Class: Bivalvia
Order: Mytilida
Family: Mytilidae

Dorsoventral symmetry
Two valves
Growth lines
Umbo

Set 1:
Original shell material
Set 2:
Mould of boring in which the shell lived (can see the structure of the Coral Rag)

Lithophaga bore into hard substrates, and often preserve as the specimen from Set 2 has, as moulds of the borings they make. They lived as suspension feeders.

Lithophaga bore into rocks by secreting a weak acid. This dissolves calcareous substances, sometimes including other bivalve shells, into which the animal bores.

Opis virdunensis Buvignier

Jurassic

Phylum: Mollusca
Class: Bivalvia
Order: Carditida
Family: Astartidae

Two valves
Hinge
Adductor muscle scars
Dorso-ventral symmetry

Internal mould

Dimyodon nilssoni

Cretaceous

Phylum: Mollusca
Class: Bivalvia
Order: Ostreoida

Cemented onto fish vertebra

Identification of these as bivalves took a very long time (historically) as few features are preserved. However, knowing that these are bivalves they can be easily spotted throughout much of the Jurassic and Cretaceous, cementing to hard substrates. The shape of the valve (of which only the inner layer remains) gives probably the most distinctive feature for this kind of animal.

Ordovician to recent

Phylum: Mollusca
Class: Bivalvia
Order: Ostreoida
Family: Pectinidae

Ribs
Growth lines
Characteristic 'fan' shape (Pecten only)

Original shell material

Pecten can escape attention predators by swimming away. They can swim in short bursts by clapping their two valves together quickly.

They live a nektobenthic lifestyle: sitting on the seafloor for the majority of the time, swimming to escape danger.

Watch a Pecten maximus swim: Video