Fig. 1. Experimental set-up for in vivo experiments at in situ pressure (26 MPa) (modified from Ravaux et al., 2003). (A) The pressure vessel IPOCAMP (Incubateur Pressurisé pour l'Observation et la Culture d'Animaux Marins Profonds; internal diameter 20 cm, height 60 cm) contains two PVC cages (length 6 cm, width 5 cm, height 6 cm) closed at the top with a transparent polyethylene lid. Three sapphire windows in the pressure vessel lid allow the insertion of an endoscope and two optical-fibre light-guides, for the observation of the inside of the cages. Large arrows indicate the inlet and outlet of circulating seawater, which is forced through the cage ventilation holes via a PVC tube. Two Pt100 probes are positioned in the water flow indicating the upstream (T1) and the downstream (T2) temperature. (B) Temperature profiles for a typical heat shock (HS) experiment (solid line, T1 probe; broken line, T2 probe; bold line, mean temperature obtained from T1 and T2 probes). The animals were maintained at 15°C and subsequently exposed to a sharp heat shock at 30–33°C. After rapid cooling to 15°C, the animals were recovered at different times after the heat shock (see Materials and methods for more details). (C) Video view of a cage containing eight P. grasslei specimens, maintained at a temperature of ca. 30°C during a HS experiment. The approximate length of P. grasslei specimens was 7 cm.