Otodistomum plunketi Fyfe 1953, is a relative rare but broadly hosted trematode known from three Orders in Class Chondrichthyes (Gibson, D.I. and Bray, R.A. 1977. Bull. Br. Mus. Nat. Hist. [Zool. Ser.], 32:167-245). In 1978, nine O. plunketi were collected from the Portuguese shark, Centroscymnus coelolepis Bocage and Capello -- a new host captured in the northeast Atlantic. Two of these nine, which were from the coelom of the same host shark, exhibited raised lesions. Closer examination of one of the specimens, a large flounder-shaped fluke measuring 27 mm x 14 mm x 3.1 mm, revealed that multiple, round, dome-shaped protrusions up to 2 mm in diameter occurred on both sides but none extended all the way through the parasite. Hematoxylin and eosin-stained serial sections of one of the excised protrusions revealed a highly cellular, unencapsulated lesion compressing the primitive mesenchyme and distending the overlying tegument. Tumor cells were basophilic and pleomorphic. Nuclei were large, occasionally indented and sometimes vesiculated. Nucleoli were prominent. Cytoplasms were granular, pleomorphic and in some cases drawn out into long, neurofibril-like processes. Both normal and abnormal mitotic figures were seen. Based on the similarity of the cells with normal ganglion cells, the lesion was diagnosed as a ganglioneuroblastoma.

Sections of several of the other protrusions revealed a central area of liquefied necrosis enclosed in compressed mesenchyme. There was no similarity of the ganglioneuroblastoma or to any other neoplasm.

This is the first neoplasm from Phylum Platyhelminthes and phylogenetically this trematode is the most "primitive" animal known with a neoplasm. Neoplasms are well known in mollusks and arthropods and recently Andres (Nat. Cancer Inst. Monogr., in press) reported finding the src gene in a broad spectrum of invertebrates from mollusks to sponges. This suggests that neoplastic transformation is universal in the animal kingdom. The surprising thing is not that this trematode tumor was found, but why the discovery of invertebrate cancers is not a common occurrence.