Particle processing on the labial palps of Mytilus edulis and Placopecten magellanicus (Mollusca:Bivalvia)

Abstract

In order to understand particle processing on the labial palps of suspension-feeding bivalves, mucocyte mapping and visual observations were performed on adult Mytilus edulis (Fam. Mytihdae) and Placopecten magellanjcus (Fam. Pectinidae] Mucocyte contents were divided into categories depending on staining affinity for periodic acid-Schiff and alcian blue. The mucocyte distr~bu-tion was determined by counts at representative sites on the palps, done on stained whole mounts or histological sections. Functional correlates for M. edulis were obtained using video endoscopy; this technique was compared to observations of carmine particle transport on specimens from which 1 valve had been removed. Video endoscopy was precluded in P. magellanicus due to the large and extremely sensitive arborescent lips; the behaviour of carmine particles deposited on the palps was therefore observed for this species. Mucus-particle cords are removed from the gill ventral partlcle groove by the cilia of the dorsal fold of the M. edulis palp at right angles to the current flow; highviscosity acid (AMPS) and acid-dominant (ADMPS)-containing mucocytes probably stabilize the cord at this point. The position of the retractable dorsal fold determines whether the cords are rejected or processed for ingestion. When the specimen's ingestlve capacity is overloaded, the arriving cords are transported parallel to and upon the palp crests to the palp ventral margin, and then to the posteriormost tip of the palp for rejection. This rejection pathway is characterized by transport perpendicular to or counter to current flow and high proportions of AMPS mucocytes. When the ingestive capacity of the specimen is not exceeded, mucus-particle cords are directed into the palp particle groove, where they are transformed into a slurry by the mechanical action of the palp crests and dorsal fold, and probably also the addition of low-viscosity neutral mucopolysacchandes present on the palp crests. The resulting slurry is amenable to both ingestion and particle selection; selected particles continue their anteriorward movement in the palp particle groove, while rejected particles are transported ventrally in the AMPS-rich crest troughs to join the rejection pathway along the palp ventral margin. The palp rejection site for P rnagellanicus is also the AMPS-rich ventro-posterior margin, which terminates in a mixed mucopolysaccharide (MMPS)-rich reflected tip, probably related to the valve-clapping voidance of pseudofeces. Both the oral groove and the crest summits contain almost exclusively MMPS, suggesting that in this species the labial palps are mostly Involved in ingestive particle handling, as opposed to M . edulis. Differences in gill structure and functlon may account for thls putative difference in palp function. The combination of mucocyte mapping and video endoscopy (where possible) significantly enhances our understanding of bivalve feeding mechanisms.

Effects of hydrogen sulfide on the feeding activity of Manila clam Ruditapes philippinarum

“…Mucus plays a key role in all aspects of particle processing on the gill surface (Beninger et al 1991,b, Beninger & Le Pennec 1993, Beninger & Dufour 1996, Beninger & St-Jean 1997a,b, Wotton 2004. Mucus consists of polysaccharide units with associated protein components (mucopoly saccharides; MPS).…”

Selection and processing of large suspended algae in the oyster Crassostrea gigas

“…Atkins 1937, Beninger & St-Jean 1997b, the fundamental anatomical differentiation of the filaments composing the bivalve heterorhabdic gill (principal, PF, and ordinary, OF), together with the oppositely directed particle trajectories on these 2 filament types, would appear to constitute a probable basis for particle selection at the gill in bivalves possessing such a gill type. Using endoscope-directed in vivo sampling, selection at the gill has recently been demonstrated in oysters , which possess the most complex heterorhabdic gill (partial tissue fusion, with both dorsal and ventral particle grooves).…”

Preingestive selection processes in the cockle Cerastoderma edule: mucus production related to rejection of pseudofaeces

“…Utilisation of endoscopes combined with image analysis systems led to the 'in vivo' observation of processes taking place in the gills of bivalves and contributed significantly to the understanding of basic aspects of the functioning of the filtering apparatus of bivalves (Beninger et al 1992, Beninger & St-Jean 1997a,b, Ward et al 1993, Ward 1996. The mechanisms …”

“…Resale or republication not permitted without written consent of the publisher endoscope observations and confirmed by independent histochemical and chemical analysis (Beninger & St-Jean 1997a,b, Beninger et al 1991. However, most of the studies about preingestive selection have assumed that the quantity of mucus which is rejected with the pseudofaeces is negligible .…”

“…Mucus production in bivalves has been studied in depth since the 1990s as an approach to better understand the role of mucus in particle processing, including mucocyte mapping for some species (Beninger & St-Jean 1997a,b, Beninger et al 1997. However, no quantification of this type of secretion or its consequences has been presented.…”