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text and figures from: Zeng, H., Zhao, F., Yin, Z., & Zhu, M. (2017) Appendages of an early Cambrian metadoxidid trilobite from Yunnan, SW China support mandibulate affinities of trilobites and artiopods. Geological Magazine, (ahead-of-print publication) 23 pp. Ontogeny of trilobite antennae is studied for the first time and shows a growth model of lengthening each podomere. Ontogeny of antennae in Hongshiyanaspis yiliangensis The variations in the trilobite exoskeletons during ontogeny have been studied for a long time and in many taxa. However, little is known about the ontogenetic pattern of trilobite appendages (see Hughes, 2003, 2007 and references therein). The growth of antennae during the ontogeny of trilobites can be performed via two theoretical models: (1) by addition of podomeres; or (2) by stretching of individual podomeres. In order to test these growth models, the number of podomeres, total lengths of the antennae and the average lengths of the podomeres were measured and analysed statistically from our new Hongshiyanaspis yiliangensis material, as well as the lengths of the cephalon as quantification of ontogenetic stage (Table 2). A significantly positive correlation (R2 = 0.9369) is found between the average length of the podomeres and the length of the cephalon (Fig. 15). Combined with the similar number of podomeres in nearly complete antennae in normal-sized and fully grown holaspids (Table 2; Figs 1a, b, 2a, b), the growth of antennae is interpreted to occur predominantly by the lengthening of individual podomeres. This may suggest that the number of podomeres increases during the meraspid stages but remains constant during the holaspid period, which is similar to the growth of thoracic segments.