Structure of the gill during reproduction in the unionids Anodonta grandis, Ligumia subrostrata, and Carunculina parva texasensis

Abstract

This study characterizes the morphological modifications of the gill that establish the functional isolation of the central water channels into brood chambers during reproduction. The anodontids use the entire lateral demibranch for reproduction. The water channels are permanently subdivided by additional septa, resulting in more channels, but they are about one-third the size of those in the medial gill. Immediately before egg deposition, each water channel is subdivided by the formation of two small secondary water channels that receive water from the water canals, and a large brood chamber with no direct exposure to the circulating pond water. The secondary water channels disappear 1 or 2 weeks after release of the larvae. The septal tissue at the suprabranchial chamber becomes enlarged after egg deposition and seals the dorsal opening of the brood chamber from the exhalant water. The lampsilids do not form secondary water channels and the eggs are deposited in the central water channel of the posterior half of the lateral demibranch. The septal tissue enlarges at the suprabranchial chamber after egg deposition. In addition, muscular tissue near the ostial opening of the canal and at the canal – channel junction is able to constrict the canal orifice. In all species studied, the modified gill allows little if any ambient pond water into the brood chamber, and the aqueous environment is under the control of the maternal tissues.