The cheliped stridulatory structures are described for Trizopagurus strigimanus, T. melitai, T. tenebrarum and T. strigatus.
Sound in T. strigimanus is produced during reciprocal flexion and extension of the carpo-propodite and mero-carpopodite joints of tightly apposed chelae. These underwater sounds occur as syllables, each of which is composed of damped pulses with a repetition rate of 36–303/s and a within-pulse frequency of 6–8 kHz. The maximum sound pressure level (peak to peak) 15 cm from the source was 24 dB re: 1 Pa.
The gastropod shells inhabited by T. strigimanus had a weak effect (5% pressure difference) on directional radiation of sound in the near field (5 cm) and no effect beyond 20 cm from the crabs.
Cavity resonance of the shells was predicted from a mathematical model, but only appeared important at a fundamental frequency of about 4 kHz, when tested in animals partially removed from their shells. A more significant effect was low-frequency vibration (100–300 Hz) imparted to the shells through direct contact by the hermit crab inhabitants.
Behavioural experiments suggested that the function of T. strigimanus stridulation is defensive, particularly against conspecific aggressors. This may reduce intraspecific competition for shells in Trizopagurus.