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Larval Development With Transitory Epidermis in Paranemertes peregrina and Other Hoplonemerteans

¹ Oregon Institute of Marine Biology, University of Oregon, Charleston, Oregon 97420
² Animal Systematics and Evolution, Freie Universität Berlin, Berlin, Germany

^* To whom correspondence should be addressed, at Oregon Institute of Marine Biology, P.O. Box 5389, Charleston, OR 97420. E-mail: svetlana{at}uoregon.edu

We describe development of the hoplonemertean Paranemertes peregrina from fertilization to juvenile, using light, confocal, and electron microscopy. We discovered that the uniformly ciliated lecithotrophic larva of this species has a transitory epidermis, which is gradually replaced by the definitive epidermis during the course of planktonic development. The approximately 90 large multiciliated cleavage-arrested cells of the transitory larval epidermis become separated from each other by intercalating cells of the definitive epidermis, then gradually diminish in size and disappear more or less simultaneously. Rudiments of all major adult structures—the gut, proboscis, cerebral ganglia, lateral nerve cords, and cerebral organs—are already present in 4-day-old larvae. Replacement of the epidermis is the only overt metamorphic transformation of larval tissue; larval structures otherwise prefigure the juvenile body, which is complete in about 10 days at 7–10 °C. Our findings on development of digestive system, nervous system, and proboscis differ in several ways from previous descriptions of hoplonemertean development. We report development with transitory epidermis in two other species, review evidence from the literature, and suggest that this developmental type is the rule for hoplonemerteans. The hoplonemertean planuliform larva is fundamentally different both from the pilidium larva of the sister group to the Hoplonemertea, the Pilidiophora, and from the hidden trochophore of palaeonemerteans. We discuss the possible function and homology of the larval epidermis in development of other nemerteans and spiralians in general.

Abbreviations: Ap, apical organ • Cg and CG, cerebral ganglia • CO, cerebral organ • DC, dorsal brain commissure • EC_D, ciliated cell of definitive epidermis • EC_L, ciliated cell of larval epidermis • Ecm, extracellular matrix • Ep, epidermis • Fgt, foregut • GC, gland cell • Gt, gut • lnc, LNC, lateral nerve cord • Mgt, midgut • Ms, body wall muscles • NM, nerve muscles • Nu_D, nucleus of definitive epidermis cell • Nu_L, nucleus of larval epidermis cell • Oc, ocellus • Pb, proboscis • Pc, posterior cirrus • St, mouth • VC, ventral commissure of cerebral ganglia • Y, yolk

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				R. B. Emlet, S. A. Maslakova, A. L. Shanks, and C. M. Young Biological Bulletin Virtual Symposium: Biology of Marine Invertebrate Larvae Biol. Bull., June 1, 2009; 216(3): 201 - 202. [Full Text] [PDF]