Swimming veliger larvae are often observed in suprabrachial or infrabranchial chambers (Chaparro et al.
Figure 3 shows numerous early veliger larvae in the infrabranchial chamber.
The embryos or larvae are then raised in the mantle cavity, suprabranchial, or infrabranchial chamber of the female (Buroker 1985, Chaparro et al.
Early veliger larvae located in the infrabranchial chamber showed a well developed velum covered with cilia (see Figs.
yessoensis (Kingzett, 1993), separating the infrabranchial
and suprabranchial cavities.
Hemolymph pressure was monitored in the infrabranchial and pericardial sinuses using indwelling catheters (polyethylene, PE 190; OD = 1.7 mm, ID = 1.19 mm) connected to strain gauge pressure transducers (Gould P23ID; Gould-Statham, Oxnard, CA).
For infrabranchial sinus pressures, the catheter tip was inserted to a depth of about 1 mm through the arthrodial membrane at the base of the fifth leg.
Hemolymph pressure in crabs is relatively variable, particularly in the sinuses where we made measurements: the pericardial space (downstream from the gill circulation) and the infrabranchial sinus (upstream from the gill circulation).
Venous hemolymph pools in the infrabranchial sinus (the high-pressure end of the gill circulation), just upstream from the gills, moves through the gill hemolymph channels, and collects in the pericardial sinus (the low-pressure end) in which the ventricle is suspended.
Hemolymph passes through the tissues, where oxygen is consumed, and returns to the infrabranchial
sinus just before it passes through the gills, where it is oxygenated.
All species of the genus Ostrea brood their embryos in the infrabranchial
chamber (Millar and Hollis, 1963; Galtsoff, 1964; Chanley and Dinamani, 1980; Harry, 1985; Cranfield and Michael, 1989).
Blood was taken anaerobically into a hypodermic syringe from the pericardial and infrabranchial
sinuses, and pH and P[O.sub.2] were measured with a Radiometer BMS1 Blood Gas System.