title used in learnabout sections of A SNAIL'S ODYSSEY

There are at least 4 reproductive patterns in tubeworms: 1) brooding outside of tube, 2) brooding inside of tube, 3) broadcasting gametes, and 4) poecilogony (mixed pattern). Most species produce some sort of free-living larva.

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  A general account of larvae begins this section on reproduction, followed by SPECIES THAT BROOD OUTSIDE OF TUBE, SPECIES THAT BROOD INSIDE OF TUBE, SPECIES THAT BROADCAST GAMETES, and SPECIES THAT ARE POECILOGONOUS, considered in other sections.
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Research study 1

drawing showing food-particle capture in a tubeworm larvaphotographs of developmental stages of tubeworm Schizobranchia insignisMany tubeworms produce free-swimming trochophore-type larvae, but whether they feed or not depends upon the taxon.  Larvae of marine invertebrates that have evolutionarily lost the requirement for feeding usually also lose the structures involved in capturing, ingesting, and digesting food.  Studies at Friday Harbor Laboratories, Washington, however, show that at least one species of tubeworm, Schizobranchia insignis, has a functional ciliary system for capturing and concentrating food particles, but that is the end of it. The larvae lack a functional gut and the food particles are rejected.  Note in the drawing on the Left that food particles are able to be captured by the cilia of the prototroch and directed to the food groove. Capture of particles is aided by the metatrochal cilia. Particles rejected at the mouth are moved posteriorly by cilia of the neurotroch. In other tubeworm larvae the edible particles are ingested and soon pack the gut. In S. insignis, however, the mouth has no connection to the midgut which, in any case, is compressed to small size by cells swollen with energy reserves. The author hypothesises that these sabellids may have lost the ability to feed relatively recently, or the ciliary bands may have an alternate function, perhaps swimming.  The prototrochal bands clearly function in swimming in other polychaete larvae, whether the larvae are feeding or nonfeeding.  Other functions considered by the author are tube formation and possible involvement in settlement.  Pernet 2003 Biol Bull 205: 295.

NOTE  in laboratory culture at 8-10oC the embryos become trochophores 2d after fertilisation, and are competent to settle and metamorphose 3-30d after fertilisation