Transformation of Phytoplanktivorous Larvae into Predatory Carnivores during the Development of Polinices lewisii (Mollusca, Caenogastropoda)

Abstract

We studied morphogenetic events that transform phytoplanktivorous larvae of a naticid gastropod into predatory juveniles that drill and ingest bivalves and ostracods within 3-5 days of metamorphic induction. Larvae of Polinices lewisii were cultured through meta- morphosis and histological sections were prepared of 9 larval and 2 post-metamorphic stages. Rapid, metamorphic transformation of feeding and gut structures is accomplished by destruction of larval tissues (velum, large areas of larval esophagus, and gastric shield of the stomach) and by prior formation during the larval stage of various juvenile/adult structures (accessory boring organ, esophageal gland, and buccal mass with jaws, cartilages, intrinsic musculature, salivary glands, and radula). Advanced differentiation of the post-metamorphic buccal mass during the larval stage is possible because the buccal cavity and radular sac develop from a semi-isolated outpocketing of the larval esophagus that does not interfere with the functioning of the larval esophagus. At metamorphosis, the buccal cavity punches out a new mouth opening in the ventral lip of the larval mouth, the larval mouth is sealed shut, and the distal part of the larval esophagus is destroyed. The epithelia forming the oral tube and buccal cavity in predatory adults of P. lewisii have a different developmental origin than the corresponding epithelia in many other adult gastropods.