229.
Nudibranchs (Mollusca, Gastropoda) feeding on tentacles and polyps of Cnidaria thereby ingest both latent and discharged nematocysts
(NCs) along with the food mass. In eolid nudibranchs (Opisthobranchia, Aeolidacea), many of the undischarged NCs are transported
to terminal cnidosacs in their body appendages (cerata) and incorporated as kleptocnidae for defense. In the present report,
the occurrence and fate of NCs in the digestive tracts of eolids is compared with hydrozoan-feeding dendronotacean nudibranchs
(Opisthobranchia, Dendronotacea), which may show more basic stages in the evolution of cnidosacs. Tomographic reconstructions
of the distal tips of cerata were composed from series of semithin light microscopic sections, utilizing 3D-surface rendering
software.
Doto acuta (Dendronotacea, Dotidae) does not have cnidosacs; transmission electron micrographs show that the NCs are digested in lysosomes
of digestive gland cells. In contrast, species of the genus
Hancockia (Dendronotacea, Hancockiidae) have several small cnidosacs in each ceras; they accumulate NCs in the digestive cells, as
well as in the cnidosacs. Many of the cnidosacs were found open to the exterior with NCs in the process of expulsion. These
and other structural details suggest assigning a function of expelling the NCs to the
Hancockia spp. cnidosacs. It is proposed that cnidosacs similar to those of
Hancockia spp. provide a clue to understanding how the defensive function of eolid cnidosacs may have evolved.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
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