Water entering the siphon passes through the perforated branchial sac, where food filtration occurs.
Stigmata of the delicate branchial sac observed were long and narrow.
The branchial sac has 13 folds in total, consistent with modern descriptions of Pyura discoveryi (Monniot et al.
However, loose sediment is also a threat to filter feeders; clogging of branchial apertures and the stigmata of the branchial sac can be fatal (Segelken-Voigt et al.
The water of Prydz Bay constantly carries large inorganic particles of glacial origin, which must be filtered out before reaching the branchial sac (Kowalke et al.
Excess water is pumped from the pharynx through the gill slits, into the branchial sac, and through the gill pore to the outside (Fig.
planktophilus appears capable of ingesting particles ranging from 0.2 [micro]m to 28.4 [micro]m , and the largest size to pass through the gill slits, branchial sac, and gill pore was 5.8 [micro]m.