The Role of Elytra in the Movement of Water Over the Surface of Halosydna brevisetosa (Polychaeta: Polynoidae)
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In intact worms ciliary tracts on the parapodial lobes and dorsal body surface bring in a flow of water laterally between parapodial lobes and carry it posteriorly along the body dorsolaterally below each row of elytra. The elytrae are not ciliated and exhibit no fanning or pumping motions, but are so shaped as to direct the incoming lateral flow posteriorly, and to contain and direct the posterior flow over the more or less corrugated dorsolateral body surfaces. They also permit the currents to operate effectively when worms are wedged into the secluded crevices and situations which they tend to seek during daylight hours. Thin areas of the body wall are provided with an external flow of water moving in one direction and an internal flow of coelomic fluid moving the opposite direction, and are presumed to function in respiratory gas exchange.