Meeting Abstract

91.7  Thursday, Jan. 7  Axes and organs in nemertean larvae: Development of a hoplonemertean HIEBERT, Laurel/S*; MASLAKOVA, Svetlana/A; Oregon Institute of Marine Biology; Oregon Institute of Marine Biology lhiebert@uoregon.edu

Nemerteans display two major modes of larval development: via a juvenile-like planuliform larva, found in the paleonemerteans and hoplonemerteans, and via the unique planktotrophic pilidium larva, which is restricted to the pilidiophoran clade. Planuliform larval development is relatively poorly understood. Here, we describe the larval development of the hoplonemertean Pantinonemertes californiensis using confocal fluorescence microscopy, providing the foundation for future studies of developmental gene expression patterns. We discover that by 48 hours after fertilization, the planuliform larva develops two pairs of epidermal invaginations that disappear by day four. The anterior pair resembles the cerebral organ rudiments of other planuliform nemertean larvae, while the homology of the posterior pair is uncertain. Similar to several other hoplonemerteans, P. californiensis posesses a transitory larval epidermis. We observed shedding of the cells of the larval epidermis on day five of development. All major organ rudiments are present in the five-day-old larva, including the gut, the cerebral ganglia, the lateral nerve cords and the proboscis. Finally, we present preliminary data on the expression of Hox genes in development of P. californiensis and the pilidiophoran Micrura alaskensis, which may help illuminate how the pilidium evolved from the planuliform larva found in basal nemerteans.