Calymene Fossil Trilobite Arthropod Prehistoric Devonian Collection (2)

Trilobite Sea Invertebrate Fossil mm 83 x 53 x 25 gr 117 Calymene (Synhomalonotus) tristani Arthropods Trilobitomorphs Phacopids Extinct Prehistoric Paleozoic Devonian Collecting Paleontology Museum.

Pleasant fossil find of Trilobite Phacopida from the Middle Devonian, representative collection specimen of good quality, with clear details of the well-preserved metameric three-lobed structure, and an appreciable visibility of the head or pygidium.
The specimen may present imperfections or signs of restoration.
Only a piece, as in photo.

Trilobites are marine Arthropods exclusive of Paleozoic era, lived by the Lower Cambrian (520-530 moy) to the late Permian (250 moy).
Their name means "three lobed", their most obvious morphological characteristic, the partition of the body into three longitudinal lobes: one axial lobe (center) and two pleural lobes (side). They are forms generally small to medium size from a few millimeters to about ten centimeters long, exceptionally up to some decimetres. Trilobites have an exoskeleton partly organic and partly composed of calcium carbonate. These animals have a head with compound eyes, a metameric segmented and articulated thorax and a rear shield pigidium. They also have a pair of jointed appendages on each segment of the body.
Up to date have been determined about 1,500 genera and 10,000 species of trilobites lived 270 million years in the overall life of this group. The trilobite are good fossil-guide, featuring a wide geographical spread, very important for the dating of the Paleozoic sedimentary rocks.

The gen. Calymene, which means "beautiful crescent moon", in reference to the cephalic glabella, is an extinct genus of Trilobites Arthropods of the order Phacopida, suborder Calymenina, whose remains have been found in North America, South America, Europe, Africa and Australia in terrain ranging from the Lower Silurian to the Middle Devonian (435-365 million years ago).
Calymene had a semicircular head (cephalon), with a high, convex glabella protruding from the anterior margin. As with many representatives of the order Phacopida, there were no spines on the margins of the body and the pleurae were decidedly rounded. The thorax was very elongated and had at least 13 segments, narrowing towards the back, or pygidium. This was short, divided into six very marked rings and a decidedly marked apex. This species reached a length of up to 9 centimeters.
The Calymene was a Trilobite that lived near the seabed and fed on small organisms present in the mud and on organic particles suspended in water. To defend itself from predators, this animal could curl up in a ball: some fossils, in fact, show this animal rolled up into a ball. This ability was even more accentuated in similar forms, such as Flexicalymene. Among the best-known species of Calymene, the type species Calymene blumenbachi is worth mentioning.