THE RELATIONSHIP BETWEEN THE UNILATERAL SIPHONAL ORGAN AND LABIAL PALPS OF MACOMA CONSTRICTA (BRUGUIÈRE, 1792) (BIVALVIA: TELLINIDAE)

Abstract

Macoma constricta has unequal siphons, the inhalant being longer and larger. Living animals were collected from muddy sand where they laid on the left valve with the long axis of the shell more or less horizontal. In dissected individuals, sand grains and detritus were identified in the ventral pallial channel and the digestive tract, indicating a normal habit of deposit feeding. Where the inflow of water occurs, a siphonal organ is present on the left mantle lobe. The labial palps are well developed and capable of considerable contraction and extension. Four thin plicae occur on the subterminal tip of the left inner labial palp and show slow undulatory movements. Palp plicae are localized near the thin distal wall of the unilateral siphonal organ. Studies of the anatomies of the labial palp and siphonal organ identified ciliary currents on the latter. The functions of the few palp plicae and siphonal organ are associated with the monitoring of water quality incursing the mantle cavity. The siphonal organ may also assist the palps in re-sorting particles in the mantle cavity.