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"Four stages in the development of the trilobite Agnostus nudus. A, Youngest stage with no mesosomatic somites; B and C, stages with two mesosomatic somites between the prosomatic and telsonic carapaces; D, adult condition, still with only two free mesosomatic somites." — The Encyclopedia Britannica, 1910

Agnostus Nudus

"Four stages in the development of the trilobite Agnostus nudus. A, Youngest stage with no mesosomatic…

"The trilobite's general form is shown in the annexed figure of the <em>Calymene Blumenbachii</em>; they possessed well-formed, compound, faceted eyes, which are frequently well-preserved in the fossil state. The body is usually divided into three regions, of which the first and last are commonly in the form of the semicircular plates, while the middle portion exhibits distinct segmentation, and by its flexibilty enabled the animal to double itself up in the manner of the common wood-louse." &mdash; Goodrich, 1859

Calymene

"The trilobite's general form is shown in the annexed figure of the Calymene Blumenbachii;…

"So-called "trilobite stage" of Limulus polyphemus. A, Dorsal; B, ventral view." &mdash; The Encyclopedia Britannica, 1910

Limulus Polyphemus

"So-called "trilobite stage" of Limulus polyphemus. A, Dorsal; B, ventral view." — The Encyclopedia…

The trilobite was an early animal on earth during the Primordial Period.

Trilobite

The trilobite was an early animal on earth during the Primordial Period.

"Vertical cross-section of a Trilobite (Calymene). i., Intestine; s., shield; L., endopodite; e., exopodite; b., epipodial parts." -Thomson, 1916

Trilobite

"Vertical cross-section of a Trilobite (Calymene). i., Intestine; s., shield; L., endopodite; e., exopodite;…

A trilobite (Paradoxides Bohemicus) of the Cambrian period.

Trilobite

A trilobite (Paradoxides Bohemicus) of the Cambrian period.

A track of the early life form, the trilobite.

Trilobite Track

A track of the early life form, the trilobite.

Asaphus is a genus containing at least 35 species of Ordovician trilobites found primarily in Europe. All were benthic predators or detritivores. The typical individual was about 2&ndash;7.5 cm in length. The cephalon was smooth, and the glabellum tends not to be distinct from the cephalon. The segments of the pygidium are fused together, though some hint of segmentation may be apparent.

Asaphus Gigas a Trilobite

Asaphus is a genus containing at least 35 species of Ordovician trilobites found primarily in Europe.…

Trilobites ("three-lobes") are extinct marine arthropods that form the class Trilobita. Why the trilobites became extinct is not clear. Their numbers began to decrease with the appearance of the first sharks and other early gnathostomes (jawed vertebrates) in the Silurian and their subsequent rise in diversity during the Devonian period. Trilobites may have provided a rich source of food for these new animals.

Dicellocephalus Minnesotenis a Trilobite

Trilobites ("three-lobes") are extinct marine arthropods that form the class Trilobita. Why the trilobites…

Trilobites ("three-lobes") are extinct marine arthropods that form the class Trilobita. Why the trilobites became extinct is not clear. Their numbers began to decrease with the appearance of the first sharks and other early gnathostomes (jawed vertebrates) in the Silurian and their subsequent rise in diversity during the Devonian period. Trilobites may have provided a rich source of food for these new animals. Fossilised trilobites are often found enrolled (curled up) like modern woodlice for protection; evidence suggests enrollment helped protect against exploitation of arthropod cuticle weakness by Anomalocarid predator attacks.

Dicellocephalus Minnesotenis a Trilobite

Trilobites ("three-lobes") are extinct marine arthropods that form the class Trilobita. Why the trilobites…

Trilobites ("three-lobes") are extinct marine arthropods that form the class Trilobita.The earliest trilobites had complex, compound eyes with lenses made of calcite, a unique characteristic of all trilobite eyes. The trilobite eyes were typically compound, with each lens being an elongated prism. The number of lenses in such an eye varied: some trilobites had only one, while some had thousands of lenses in a single eye. In these compound eyes, the lenses were typically arranged hexagonall (b).

Dicellocephalus Minnesotenis a Trilobite

Trilobites ("three-lobes") are extinct marine arthropods that form the class Trilobita.The earliest…