page_title: Agnostus
section_title: Appendages
hierarchical_section_title: Agnostus / Description / Appendages
caption_attribution_description: English: Drawing of the most forward thorax appendix of a late meraspis instar of Agnostus pisiformis, based on Whittington, H. B. et al. (1997). Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida, page 90, figure 79. The coxa is connected to the ventral side of the thorax. The side of the coxa facing the midline (upside in the drawing) carries spines and is called the gnatobasis. A pair of opposing gnatobases probably acted as jaws. The coxa also carries two arms: the ventral endopodite, which consist of 7 sections called podomeres (en1 to en6 and the terminal clawlike podomere) and the lateral exopodite, which consists of two podomeres (ex1 and ex2). The endopodite segments carry spines toward the midline and thumblike extensions laterally. The exopodite terminates with four spines called seta (plural setae). Total length ¼ mm.
context_page_description: Agnostus is a genus of agnostid trilobites that lived during the upper Middle Cambrian–lower Upper Cambrian. It is the type genus of the family Agnostidae. It is subdivided into two subgenera, Agnostus and Homagnostus.
context_section_description: The appendages of meraspid developmental stages of Agnostus pisiformis (½-1 mm total body length) are the best preserved of any trilobite found so far. Agnostus pisiformis has nine pairs of appendages, the antennules, and eight pairs of "legs", that differ in size and composition. Four pairs of appendages originate from the cephalon, two from the thorax, and three from the pygidium. The frontal antennules are short and stout. The most forward pair of "legs" has a small coxa, a seven-podomere exopodite carrying long, bristle-like setae and gill-like extensions, and no endopodite. The second pair has a five-podomere exopodite and a six-podomere endopodite. The third has a three-podomere exopodite and a six-podomere endopodite. The fourth has a two-podomere exopodite and a seven-podomere endopodite. The fifth has a single-podomere exopodite and a six-podomere endopodite. Further appendages are more and more reduced in size and complexity.
caption: Drawing of a biramous leg of Agnostus pisiformis
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