Invertebrates in the Plankton: Chordata

Like vertebrates, larvaceans are members of the phylum Chordata, which all share a dorsal nerve cord, gill slits, and a notochord (stiffening structure in the tail) at some stage of development.  All larvaceans are planktonic.  Oikopleura is a  larvacean that feeds by secreting an elaborate mucous house around itself, which is used to trap small invertebrates.  The house has paired incurrent openings covered with a filter. The filter keeps out unwanted large organisms and lets in smaller invertebrates which are sucked into the pharynx. 

Oikopleura sits inside its house beating its tail to propel itself through the water. The current forces water and food in. The house often becomes clogged with waste and then a new mucous house must be secreted. This same house protects the organism and keeps it from sinking in the water column.

The house is a fragile structure, and it takes a skilled planktonic biologist to collect the animal with its house intact.

Sexual reproduction in Oikopleura occurs by the release of sperm through tiny ducts and the rupture of the body wall to release eggs. All larvaceans are hermaphroditic, but self fertilization does not occurs.  In the photos on this page, gonads are stored in the large globose structure at the end of the body. Oikopluera die soon after reproducing.

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