Orenus - Orenus

...Fossils have often been found in which the body is curled up, with the ventral side of the head and the ventral side of the tail joined together, which is thought to have been a type of defensive posture.
[Systematics and Classification]
Trilobites reached their peak in the Cambrian to Ordovician periods, and many of them, such as Redolia, Olenus , and Olenellus, are considered to be global index fossils. They also form animal groups that are geographically distinct.

*Some of the terminology explanations that mention "Olenus" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…体を丸めて頭部腹面に尾部腹面を合わせた撓曲（どうきよく）姿勢の化石もしばしば見いだされ，一種の防御体制をとったものと考えられている。
［系統･分類］
　三葉虫類は，カンブリア紀～オルドビス紀に全盛期をもち，レドリキア，オレヌスOlenus，オレネルスOlenellusなどのように世界的な示準化石とされるものも多い。また，地理的に特徴のある動物群をなすこともある。…

※「オレヌス」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報