Horseshoe Worm Larva

Horseshoe worms, phylum Phoronida, are worm-shaped, solitary, tube-dwelling lophophorates. The lophophore is a specialised feeding structure (common also to brachiopods and bryozoans) that takes the form of a ciliated tentacular crown surrounding the mouth and aids with filter-feeding, respiration and protection. These exclusively marine organisms, when adult, live on the sea floor in chitinous tubes which they secrete, two to three mm in diameter and greater than 10 cm in length. However, the preceeding developmental stage is a free-swimming larva, an actinotroch, that has a pelagic life of approximately 10-20 days before it settles out and undergoes metamorphosis.

The actinotroch larvae (see above) are thought to be some of the most beautiful members of the marine plankton. They swim gracefully with a hood upright and their ciliated tentacles spread out like a canopy. The ciliary band at the rear end acts as a rear propeller for locomotion.

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