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.