Anatomy of finfish and shellfish

Unit 13 - Mollusca

13.2.5. Mantle or Palliun
Beneath the shell, the soft body of the mussel is enveloped in a thin, semi-transparent and soft covering of skin, called the mantle or pallium, which secretes the shell. It also consists to lateral halves, the mantle lobes or folds, which are continuous dorsally. Each mantle lobe is a thin sheet of tissue, closely applied to the inner surface of the valve. The ventral free border of each mantle lobe is thickened and contains muscles which insert upon the pallial line.

Fig. 5. Unio. Animal with left shell removed

At the posterior end, the mantle lobes are thick¬ened, muscular and form two short tubes or siphons. The current of water enters through the ventral incurrent or inhalent siphon and leaves through the dorsal excurrent or exhalent siphon. The inhalent siphon is wider, with a fimbriated or papillated margin and formed simply by coming together of the two mantle lobes. The exhalent siphon is narrower, with smooth margin, and formed by the fusion of the two mantle lobes. On the postero-dorsal side, the two mantle lobes also form a dorsal mantle pore.
Histologically, the mantle consists of—

• an outer columnar epithelium beset with numerous unicellular glands secreting nacre,
• a middle fibrous connective tissue, and
• an inner ciliated epithelium containing mucus-secreting cells.