''Ogygiocarella'' Brongniart, 1822, is a genus of asaphid

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s. It occurred during the Middle

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

Etymology

The generic name, ''Ogygiocarella'', refers to "Ogygia", the seventh daughter of

Amphion There are several characters named Amphion in Greek mythology: * Amphion, son of Zeus and Antiope, and twin brother of Zethus (see Amphion and Zethus). Together, they are famous for building Thebes. Pausanias recounts an Egyptian legend accor ...

and

Niobe In Greek mythology, Niobe (; grc-gre, Νιόβη ) was a daughter of Tantalus and of either Dione, the most frequently cited, or of Eurythemista or Euryanassa, the wife of Amphion and the sister of Pelops and Broteas. Her father was the r ...

, which name is combined with "-care-", from the Greek "akares", meaning short, and finally "-ella", the diminutive form.

History

''Ogygiocarella'' is arguably the first trilobite that was scientifically described. Rev. Edward Lhwyd published in 1698 in The

Philosophical Transactions of the Royal Society ''Philosophical Transactions of the Royal Society'' is a scientific journal published by the Royal Society. In its earliest days, it was a private venture of the Royal Society's secretary. It was established in 1665, making it the first journa ...

, the oldest scientific journal in the English language, part of his letter “Concerning Several Regularly Figured Stones Lately Found by Him", that was accompanied by a page of etchings of fossils. One of his etchings figured a trilobite he found near

Llandeilo Llandeilo () is a town and community in Carmarthenshire, Wales, situated at the crossing of the River Towy by the A483 on a 19th-century stone bridge. Its population was 1,795 at the 2011 Census. It is adjacent to the westernmost point of the ...

, probably on the grounds of Lord Dynefor's castle, he described as “… the skeleton of some flat Fish …".

Distribution

* ''O. debuchii'' occurs in the Middle Ordovician of Wales (late Llanvirn, Lampeter Velfrey, Abereiddi Bay). * undetermined ''Ogygiocarella'' specimens have been found in the Middle Ordovician of Wales (early to late Llandeilo, Llandeilo Sandstone-siltstone facies, Llandeilo; Pencerrig Lake, near Builth Wells, Powys).

Description

''Ogygiocarella'' has a very flat calcified dorsal exoskeleton, with an oval outline (about 1½× longer than wide). The headshield (or cephalon) is 2½× wider than long, and of equal size as the tailshield (or

pygidium The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compo ...

), a state called isopygeous. Both are semicircular. The backcorners of the cephalon end in so-called genal spines that stick backwards approximately to the 6th thorax segment. The central raised area of the cephalon (or

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior to ...

) has 4 pairs of furrows and expands in front of the eyes. The eyes are small, close to the glabella and in the rear half of the cephalon. The dorsal facial sutures, that split when moulding, arch from the front of the eye and pass in front of the glabella. The suture follows the top of the visual surface, as in all trilobites, and from there cut backwards and outwards at approximately 45° to reach the posterior margin of the cephalon approximately halfway between the glabella and the lateral border. As usual for members of the family Asaphidae, it has 8 articulating segments in the middle part of the body (or

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

). The axis is about half as wide as the ribs (or pleurae) to each of the sides. In the thorax the axis tapers slightly towards the back. In the pygidium the axis tapers stronger and terminates a short distance from the margin in a roundish endpiece. It has 10-14 ribs on each side of the axis, which fade-out in the border that is as wide as the axis.

References

External links

* {{Taxonbar, from=Q7080316 Asaphidae Asaphida genera Fossils of Wales Ordovician trilobites