The morphological differences between adults of Chthamalus challengeri Hoek and of Euraphia pilsbryi (Hiro) were compared to investigate the phylogenetic relationship of subfamilies Chthamalinae and Euraphiinae. The morphological differences between them are lesser, however, the suture of scutum and tergum, adductor muscle pit of the scutum, the number of mandibular teeth, and presence or absence of grapple spine of the second cirri are morphologically distinct between them.
Furthermore, the larval stages of C. challengers and E. pilsbryi were described based on larvae reared in the laboratory. Rounded cephalic shield, absence of posterior shield spine, unilobed labrum, and same ratio between length and width of cephalic shield are identical between two species. However, the appearance time of plumose setae in antenna and mandible of metanauplius of C. challengeri is distinctively different from E. pilsbryi and other Euraphiinae nauplii.
Therefore, the larvae of E. pilsbryi show a closer relationship to those of the subfamily Chthamalinae than the subfamily Euraphiinae in the larval ontogeny. However, the adults of E. pilsbryi closely resemble to those of the subfamily Euraphiinae in the external morphology.

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