New record of underexplored sand dollar <i>Peronella</i> (Echinoidea: Laganidae) from Taiwan

The genus Peronella Gray, 1855 is a widespread group of sand dollars native to the Indo-Pacific region. However, compared to adjacent areas, their presence in Taiwan is extremely limited, with only two recorded species, including one only represented by a single denuded test. Here, we report new Peronella specimens from northern Taiwan. Based on petal outline, lateral outline, apical system, periproct position, and oral plating pattern, these specimens are identified as Peronella pellucida Döderlein, 1885. Their morphological variations during growth as well as individual differences are described. We found notable intraspecific variations in the gonopore size and periproct, suggesting that some previous diagnostic features for this genus may not be reliable. In contrast, hydropore distribution and periproct position emerge as the most reliable diagnosis. Additioanlly, except for the juvenile and deformed specimens, all other specimens exhibit four gonopores, consistent with the previous key diagnosis of Peronella. Our neighbor-joining tree based on mitochondrial COI sequences of four available Peronella species reveals strong monophyletic supports for each species and that P. pellucida is phylogenetically closer to P. rubra Döderlein, 1885. Our morphological measurements, combined with molecular evidence, provide valuable data for a better understanding of this underexplored group.