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Abstract:

The data set of chaetotaxy of maxillula in the 17 species of the genus Loxoconchawas compiled.  The information of chaetotaxy in the 12 species was referred from the literatures and in the 5 species is shown here for the first time. The examined species inhabit in the coasts of Japan (13 species), Europe (2 species), Australia (1 species) and Vietnam (1 species). The differences of the chaetotaxy on three endites of maxillula are consistent with the taxonomical divisions which are estimated by the distributional pattern of pore systems, which is regarded as a useful phylogenetic index. On the other hand, the numbers of branchial and proximal setae don’t show any remarkable relationships. Additionally, there is a difference in the number of three endites’ setae between two modes of life, but no differences in the number of the branchial and proximal setae. The tendency between microhabitat and chaetotaxy is independent from the grouping by pore system.The smaller numbers of the setae are distributed in the species of the derived taxonomic group, also apart from the body size.  Since the smaller number is generally shown in the juveniles of this genus, this tendency can be considered as paedomorphism.