Monday, May 9, 2011

Coronate larva of Bugula sp.

This is a dark-field photomicrograph of a coronate larva of the gymnolaemate bryozoan Bugula sp. Our instructor, Svetlana Maslakova collected colonies of this species from the docks in the Charleston Boat Basin and kept them in the dark until 11 am of the following day. Exposure to light stimulates release of brooded coronate larvae in many bryozoans, including Bugula. Coronate larvae are lecithotrophic (i.e. non-feeding), and there is no trace of a gut, mouth or anus. These larvae are round and opaque, and covered with ciliated epidermis, called corona ciliata. Cilia of corona ciliata propell coronate larva through the water. The larvae of Bugula sp. have two eye spots, which you can see on this picture, and are able to detect the direction from which the light is coming. These coronate larvae swim toward light, and they swim very fast! Aside from the two eye spots, and some pigment spots in the epidermis, and the ciliated epidermis, larvae of Bugula sp. have few features. The most prominent of them, is perhaps the vibratile plume - the tuft of long cilia on one side, which looks like a little flame (at about 1 o’clock on this picture). Vibratile plume is a part of the pyriform organ, a glandulo-sensory structure which plays a role in selection of substrate for metamorphosis.

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