Plectothyris Plectothyris is a brachiopod from the Jurassic Period.
It is biconvex (both valves bulge outwards) with a non-strophic, or curved, hinge line.
It has no sulcus, or fold.
The line along which the two valves meet, called the commissure, is zigzagged, with
the zigzag becoming more defined towards the midline.
Each valve is ribbed towards the edge.
Also growth lines are visible towards the centre of the valve.
They formed as the valves became bigger, probably due to seasonal growth, similar to the growth rings of a tree trunk.
Details such as these help to distinguish many hundreds of types of brachiopod.
Their sea-bed habitat and their very hard and resistant shells mean that brachiopods were preserved in huge numbers and are very useful for dating rock layers.
Plectothyris Plectothyris is a brachiopod from the Jurassic Period. It is biconvex (both valves bulge outwards) with a non-strophic, or curved, hinge line. It has no sulcus, or fold. The line along which the two valves meet, called the commissure, is zigzagged, with the zigzag becoming more defined towards the midline. Each valve is ribbed towards the edge. Also growth lines are visible towards the centre of the valve. They formed as the valves became bigger, probably due to seasonal growth, similar to the growth rings of a tree trunk. Details such as these help to distinguish many hundreds of types of brachiopod. Their sea-bed habitat and their very hard and resistant shells mean that brachiopods were preserved in huge numbers and are very useful for dating rock layers.
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