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Abstract

The ontogenetic changes of the maxillula in Loxoconcha noharai Le and Tsukagoshi, 2014 from the second instar (A-7) through to the adult are described. The general development and number of setae on the maxillula of L. noharai are the same as L. japonica Ishizaki, 1968 from the second (A-7) to the fourth instars (A-5), but differences in these characters are found between the two species in and after the fifth instar (A-4). The number of setae on the endites and endopodite of the maxillula of L. noharai reaches a maximum in the pre-adult stage A-1, whereas in other species, it continuously increases throughout all ontogenetic stages. The maxillula of L. noharai bears fewer setae and claws throughout ontogeny compared with other species in different superfamilies. This tendency reflects possible paedomorphic evolution in L. noharai. In addition, the new species Loxoconcha yoshidai sp. nov., from the Okinawa Islands, southern Japan, is described herein. The distribution pattern of pore systems below the eye tubercle, which is used to divide the genus Loxoconcha into groups, shows that this new species has an unstable intermediate state between Groups B and C.