spp. nudibranchs have a shape that is quite similar to the shape of Convolutriloba retrogemma. The flatworm and the nudibranch both I \ave "tails ' and the shape of the "head" and overall silhouette is the same. A possible origin of this evolution of similar shape we will discuss shortly. Good candidates to try for flatw orm control include Chelidonura electra, C. inornata, C. amoena, C. castanea, C. flavolohata, C. fuIv¿punctata, C. livida, C. hirun-dinina, Cpunctata, C. sandrana, C. tsurugensis, C. pallida, and the exquisite C. vavians, which is black with electric blue lines. We have not had the opportunity to try all of these species, but are happy to report that one of the most beautiful ones, C. varians, quite readily eats the red flatworm Convolutriloha. It is fascinating to watch this slug eat the flatworms. It appears as if a little "tongue" is quickly everted to snatch the worms as they are sucked in. Upon closer inspection it can be seen that this "tongue" is actually a tube-like proboscis composed of two flaps curled together, and it is used like a straw. A hungry C. varians may slurp up nearly a hundred C. retrogemma per hour before it is satiated. It will later defecate large red fecal pellets.
The flatworms avoid predation by most fishes and other potential predators by accumulating in their tissues nasty pungent and probably toxic substances. They smell like a combination of iodine and putrid vegetables, not unlike Acropora spp. corals, and the red colour can leave stains on ones fingers. We suspect that the nudibranchs that eat these flatworms may further concentrate the chemicals from their prey, thus gaining the benefit of becoming distasteful or inedible. The stunning colour pattern of Chelidonura varians is no doubt aposematic, a warning to potential predators. In this regard, perhaps the shape of the nudibranch has evolved to protect the young of the species from preclation. They may be mimics of the toxic flatworms they eat. Another species in the genus, Chelidonura castanea, is coloured exactly like the red flatworm (see the book Nudibranchs and Sea Snails Indo-Paciftc Field Guide by Helmut Debelius).
Chelidonura varians is an exquisite sea slug that will certainly become popular among reef aquarists as they recognize that it eats the flat-worm Convolutriloba retrogemma that proliferates to plague proportions in well illuminated reef aquaria. The slug is an excellent candidate for aquaculture. J. Sprung
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