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Journal of Marine Biology
Volume 2013 (2013), Article ID 209496, 5 pages
http://dx.doi.org/10.1155/2013/209496
Research Article

Role of the Digestive Gland in Ink Production in Four Species of Sea Hares: An Ultrastructural Comparison

Dauer Electron Microscopy Laboratory, Department of Biology, University of Miami, Coral Gables, FL 33124, USA

Received 25 June 2013; Accepted 20 October 2013

Academic Editor: Nobuyuki Miyazaki

Copyright © 2013 Jeffrey S. Prince and Paul Micah Johnson. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The ultrastructure of the digestive gland of several sea hare species that produce different colored ink (Aplysia californica produces purple ink, A. juliana white ink, A. parvula both white and purple ink, while Dolabrifera dolabrifera produces no ink at all) was compared to determine the digestive gland’s role in the diet-derived ink production process. Rhodoplast digestive cells and their digestive vacuoles, the site of digestion of red algal chloroplast (i.e., rhodoplast) in A. californica, were present and had a similar ultrastructure in all four species. Rhodoplast digestive cell vacuoles either contained a whole rhodoplast or fragments of one or were empty. These results suggest that the inability to produce colored ink in some sea hare species is not due to either an absence of appropriate digestive machinery, that is, rhodoplast digestive cells, or an apparent failure of rhodoplast digestive cells to function. These results also propose that the digestive gland structure described herein occurred early in sea hare evolution, at least in the common ancestor to the genera Aplysia and Dolabrifera. Our data, however, do not support the hypothesis that the loss of purple inking is a synapomorphy of the white-ink-producing subgenus Aplysia.