About the Cover
Cover
The cover shows an anterior frontal view of a
recently hatched, lecithotrophic larva of the aeolid
nudibranch mollusc Berghia verrucicornis. This
species of Berghia lives on shallow reef flats in the
Caribbean in areas where its prey, the sea anemone Aiptasia pallida, is abundant. As is the case with other molluscan species, the larva of Berghia has a central nervous system that includes an apical ganglion. This ganglion contains the primary receptor
(or receptors) for the inductive chemical signal that
initiates settlement and metamorphosis in opisthobranch
larvae.
In the laser scanning, confocal, maximum intensity
projection shown, the larva has been double-labeled
with antibodies that reveal cells or cell parts that contain serotonin or tubulin. This labeling reveals a
number of serotonergic neurons (red) that are located between and below the larva's two black eyespots. Of these, the five largest are parampullary
neurons within the apical ganglion, with the three
closest to the top of the image possessing sensory
dendrites (red), the ends of which are embedded in the larva's pretrochal epidermis. These sensory neurons, as well as the two interneurons of this group of five, extend axons into the central neuropil
(red) of the ganglion. The axons originating from at
least some of these neurons then exit the neuropil
and project into the velum, a larval organ used for
both swimming and feeding. This sensory serotonergic
system is thought to be involved in modulating
activities of the velar musculature and cilia.
In addition to the velar cilia at the top of the image,
the tubulin antibody labels five tubular structures
(bright green, two on the right superimposed) in the
apical ganglion that are dense ciliary bundles. These
are present within a deep invagination of the plasmalemma
of sensory cells called ampullary neurons.
As is apparent, the invaginated ampulla of
each neuron communicates with the external environment via a long narrow canal. The ends of these canals are grouped in the pretrochal epithelium
around and among the ciliary tuft cells, the ciliary
tufts of which can be seen centrally at the top of the
image. It has been suggested that the ampullary
neurons are the actual primary receptors for the metamorphic inducer. Kempf and Page (p. 169 of this issue) use antitubulin labeling to examine the
structure and organization of the ampullary neurons
and of a new, putative apical nerve in larvae of a
number of opisthobranch species.
Credits :Confocal data collected and processed by
Stephen C. Kempf (Auburn University). Cover design:
Beth Liles (Marine Biological Laboratory).
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Copyright © 2005 by the Marine Biological Laboratory.
