Two recently-distinguished species of Chthamalus (Cirripedia) are found on rocky shores in the north-eastern Atlantic: C. stellatus predominant on islands and headlands and C. montagui more abundant in bays. Larvae of the two species were produced in laboratory cultures to describe and compare the morphology and to allow identification in plankton samples. Nauplius larvae of C. stellatus are up to 30% larger than those of C. montagui. Differences in setation are minor. The two species are easily distinguishable from the size and shape of the cephalic shield. Chthamalus stellatus has a subcircular shield with longer body processes in later stages while C. montagui is more ovoid. The former develop more slowly in culture than the latter. Chthamalus stellatus larvae in a culture at 19 °C reached stage VI in 16 d compared to 11 d for larvae of C. montagui at the same temperature. The morphology and longer development time of C. stellatus larvae suggests adaptation to a more oceanic lifestyle and wider dispersal to reach more fragmented habitats than larvae of C. montagui.
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