Key for the identification of Chthamalus species of the ‘ challengeri subgroup’ of the Northwest Pacific

1. Junction of the scutum and tergum sigmoid shaped........................................................... 3

- Junction of the scutum and tergum straight.................................................................. 5

2. Cirri III antenniform......................................................................... C. antennatus

- Cirri III non- antenniform............................................................................... 4

3. 4–5 depressor muscle crests on tergum.......................................................... C. challengeri

- 2–3 depressor muscle crests on tergum............................................................... C. dalli

4. Shell surface strongly ribbed....................................................................... C. moro

- Shell surface not strongly ribbed.......................................................................... 6

5. Scutum equilateral triangular............................................................ C. williamsi sp. nov.

- Scutum depressed, width greater than height........................................................ C. sinensis