Figure 2. (IMAGE)
Caption
Composite diagram of bivalve ctenidia as observed using video endoscopy (orientation: ventral foreground and dorsal background). Upper ctenidium represents a heterorhabdic condition (e.g., oyster), whereas lower ctenidium represents a homorhabdic condition (e.g., mussel). Suspended particles enter the pallial cavity (1) and are captured by the ctenidium at an efficiency that depends on laterofrontal ciliary structure (see Fig. 1) and particle size. Once captured, particles are transported to the margins of the ctenidium by frontal cilia. In an oyster (top), bidirectional transport and particle selection on the ctenidium is possible. Particles are transported to the VG only on the ordinary filaments, whereas particles are transported to the dorsal tract on the principal filaments or on the ordinary filaments. Material in the VG (2a) is transported in a cohesive mucous string and can be rejected directly from the groove, forming PF or directed onto the LP for further processing. Particles in the dorsal tract are transported in a mucous slurry to the LP for further processing (2b). In a mussel (bottom), almost all particles are transported to the VG by the ordinary filaments (little, if any, bidirectional transport). Material in the VG (3) is transported in a cohesive mucous string to the LP for further processing. In both oysters and mussels, particle selection on the LP results in material either being rejected as PF (4), or ingested. Figure adapted after Ward (1996).
Credit
Maria Rosa, J. Evan Ward, Sandra E. Shumway
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