Thursday, May 20, 2010

Nechtochaete larva of the polychaete Magelona

On April 5, 2010 my Comparative Embryology and Larval Biology class ventured outside the mouth of Coos Bay, OR in a small boat to do a plankton tow. A plankton tow consists of dragging a net with very small holes, in this case we used a 153 μm mesh, through the water column. The organisms big enough to get caught in the net are collected at the bottom in a small container. Once back in the lab we sorted the plankton, and I came across a polychaete nechtochaete larva with long tentacles on its head, and bundles of long chaetae, chitinous bristles found in annelids, two on each segment of the larva. I identified this polychaete as belonging to the genus Magelona (Fam. Magelonidae), because it has the characteristic pair of long tentacles, which are often coiled.
These large tentacles are thought to function as locomotory suspension organs (Wilson 1982).While observing the larva under a compound microscope I noticed that it would contract and expand the tentacles and move around under the cover slip. The chaetae found on the larva may also aid in defense against predators. The larva’s tentacles have also been hypothesized by Wilson (1982) to assist in the capture of prey. Lebour (1922) and Smidt (1951) observed bivalve veliger larvae in the guts of larval Magelona. During metamorphosis, the larval tentacles are replaced by proportionally smaller adult tentacles.

Lebour MV. 1922. The food of plankton organisms. Journal of the Marine Biological Association of the United Kingdom. 12: 644-677.

Smidt ELB. 1951. Animal production in the Danish Waddensea. Meddelelser Kommission fra Danmarks Fiskeri- og Havundersogelser. 11 (6): 151.

Wilson DP. 1982. The larval development of three species of Magelona (Polychaeta) from localities near Plymouth. Journal of the Marine Biological Association of the United Kingdom. 62: 385-401.

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