Shell removed. Dorsal view, anterior of animal at right of image, left of animal at top of image. Green pigment scraped off transparent mantle; intact except for accidental slit in roof of nuchal cavity through which distal half of the ctenidium protrudes.
The ctenidium consists of a subtantial axis (1) with many lamellae resembling the teeth of a comb attached to each side; bipectinate arrangement. The lamellae on the right of the axis are large (2), but those on its left are small and restricted to its distal part (3).
The inhalant current of oxygen-bearing seawater enters the nuchal cavity from the left and passes between the lamellae which absorb the oxygen for blood flowing through them. The oxygenated blood flows into the large branchial efferent vessel in the axis (1) and thence to the heart (4 pericardium containing auricle and ventricle) near the base of the ctenidium to be recirculated through the body.
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig