The fate of the larval epidermis in the Desorlarv

Authors: Jörn von Döhren

Publish Date: 2011/07/28

Volume: 130, Issue: 3, Pages: 189-

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Abstract

Pilidiophora constitutes a clade of nemerteans characterized by a peculiar larval type the pilidium A characteristic of this larva is the transitory epidermis in which the juvenile develops from imaginal discs The primary function of this larval envelope is assumed to be feeding and dispersal When juvenile development is complete the larval epidermis is ruptured and swallowed by the juvenile According to recent cladistic and molecular analyses of the Nemertea the intracapsular Desorlarva of the sibling species Lineus viridis and L ruber is thought to have evolved from a pelagic pilidium The general course of development has been demonstrated to be similar to that of the pilidium in which the juvenile forms from imaginal discs under the larval epidermis The two Lineus species however differ in their mode of larval feeding L ruber being ootrophic and L viridis being lecithotrophic In order to elucidate the transition from the planktotrophic pilidum to lecithotrophic development I studied the early cleavage and metamorphosis from intracapsular Desorlarva to juvenile stages in L viridis from the island of Sylt using light microscopical electron microscopical and fluorescent staining methods Due to the specific cleavage pattern with equally sized 1st quartet animal blastomeres and vegetal blastomeres in L viridis the larval epidermis later contains a considerable amount of the yolk reserve During metamorphosis the larval epidermis is ingested by the juvenile thus displaying behavior similar to that of the pilidium larva In contrast to the pilidium the function of the larval epidermis of the Desorlarva has shifted from feeding and dispersal to direct food supply Thus the development of L viridis is a perfect example for strong historical constraints that prevent ancestral larval structures from being lostI am grateful to T Bartolomaeus for helpful comments that considerably improved the quality of the manuscript I would also like to thank Lily Wescott for language editing the staff of the Wattenmeerstation List Sylt of the AWI Bremerhaven for providing facilities and accommodation during collection of L viridis and two anonymous reviewers for constructive criticism that helped increasing the quality of the manuscript considerably The study was supported by the German Research Council DFG Ba 1520/111

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