Diagram done for a journal publication by Dr. Maria Rosa on bivalve filter feeding. These were initially sketched and inked with traditional media, then scanned and cleaned in Photoshop. The labels, arrows of both figures, and the offset panel of figure1 were added in Illustrator.

Figure 1 shows a generalized bivalve ctenidium (comblike gill structure in bivalves used for respiration and food capture). Water flows through the ctenidium (gills), where food particles are captured and entrained into a mucous string. The mucous and entrained particles are transported to the edge of the ctenidia and into a ventral groove, then along the ventral groove to the labial palps (LP), where the mucous string and food particles are processed and ingested. The offset panel of Fig 1 shows a cross-section of individual filaments of the ctenidia and the location of the different cilia forms. The short frontal cilia (F) primarily transport particles along the filament. The laterofrontal cilia (LF) are responsible for particle capture and helping with particle transport along the filament. The lateral cilia (L) generate the water currents across the ctenidia, bringing in a continuous flow of oxygenated water and food particles. The top pair (B) represents bivalves that have small laterofrontal cilia (such as scallops), which create a much smaller area of hydrodynamic particle entrainment (dashed oval circles). The lower pair (C) represents bivalves with longer laterofrontal cilia (such as mussels) and the resulting larger hydrodynamic entrainment zone, contributing to higher capture efficiency for small particles. The arrows in the offset panel show the flow of water across and between filaments. Open circles represent particles before and after capture. The diagrams were created from video endoscopy observations of feeding bivalves.

Figure 2 is a composite diagram of bivalve ctenidia, observed using video endoscopy. The upper half of this "split personality bivalve" represents bivalves such as oysters, which employ bi-directional transport along filaments. In contrast, the lower half represents bivalves like the mussel, which show no significant bi-directional movement along filaments. In these diagrams, food particles enter the pallial cavity (1) and are captured by the ctenidium. Once captured, particles and mucous are transported to the margins of the ctenidium by frontal cilia. In the oyster (upper half), transport occurs bi-directionally to the ventral groove (VG) and dorsal tract (DT). Particles entrained in the ventral groove (2a) are incorporated into a cohesive mucous string. These ventral groove-transported strings can be rejected directly from the groove, forming pseudofeces (PF). Non-rejected strings from the ventral groove are delivered onto the labial palps (LP) for further processing. Particles transported to the dorsal tract are entrained in a loose mucous slurry and transported to the labial palps or processing. In mussels and bivalves with similar ctenidia structures, the filaments transport almost all particles to the ventral groove. The ventral groove (3) material is incorporated into a cohesive mucous string and transported to the labial palps for processing. In mussels and oysters, particle selection on the labial palps results in rejected particles forming pseudeofeces (4).