Extinct genus of trilobites From Wikipedia, the free encyclopedia
Trinodus is a very small to small (about 1 centimetre or 0.39 inches) blind trilobite, a well known group of extinct marine arthropods, which lived during the Ordovician (Tremadocian to early Hirnantian),[1] in what are now the Yukon Territories, Virginia, Italy, Czech Republic, Poland, Denmark, Sweden, Svalbard, Ireland, Scotland, Wales, Iran, Kazakhstan and China. It is one of the last of the Agnostida order to survive.
| Trinodus Temporal range: | |
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| A drawing of Trinodus tardus | |
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | †Trilobita (?) |
| Order: | †Agnostida |
| Family: | †Metagnostidae |
| Genus: | †Trinodus M'Coy, 1846 |
| Type species | |
| †Trinodus agnostiformes M'Coy, 1846 | |
| Species | |
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| Synonyms | |
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Trinodus is derived from the Latin tri (three) and nodus (node).
Arthrorhachis is derived from the Greek ἄρθρον (árthron, "joint") and ῥάχις (rháchis, meaning axis, spine, ridge or backbone).[1]
Trinodus, Arthrorhachis and Geragnostus are closely related and it may be appropriate to assign their species to just one genus. All species in these three genera have virtually identical cephalons, but of T. agnostiformes, the type species of Trinodus only one poorly preserved cephalon was known. However, relatively recent, pygidia assignable to T. agnostiformes were found. Although this material is distorted or incompletely preserved, it is very similar to the pygidium of Arthrorhachis tarda. Species with a rear rhachis lobe longer than the postaxial region are henceforth combined in Geragnostus, all others are assigned to Trinodus.[2]
Trinodus elspethi, which - as an agnostoid - only has two thorax segments, has at least nine larval stages (or instars), three meraspid and six holaspid, in its life. So it molted at least eight times.[18]
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