CJpn. J. Parasitol, Vol. 34, No. 2, 93-100, April, 1985] Comments on Some Problems of Taxonomy of Oncomelania Zai-bin KANG (Received for publication ; May 17, 1982) Key words: history, species, chromosome number, hybridization test, morphological characteri stics, integrative characteristics. Oncomelania It is well-known that Oncomelania snails omelanian into three genera, eighteen species are the intermediate host of Schistosoma ja- and two subspecies on the basis of such stru ponicum, which is Asian pandemic. The ctures as shell, operculum, radula, etc., pus geographical distribution of schistosomiasis hed the history of oncomelanian taxonomy cases entirely corresponds to that of Oncome into a period of enormous splitting. Later, lania snails. According to surveys made in Abbott recombined all oriental oncomelanians various endemic foci, wherever cases of sch (Continental parts as well as Taiwan Prov istosomiasis were found Oncomelania snails ince of China, Japan and Philippines) into were invariably present. But the taxonomy one genus, 4 species and one subspecies, and of those snails has been in a chaotic state thus brought about a period of enormous for a long time. In this paper, the writer merging. The result of all these revisions dwells on the following seven points. It is was that some investigators began to be ske hoped that the present work will serve as a ptical about the reliability of the basis of reference to further study on these snails. oncomelanian taxonomy ; some of them even 1. A confused history of oncomelania ta went so far as to negate entirely the taxono- xonomy : It has been 103 years since the mical basis heretofore adopted, yet they did identification of Oncomelania hupensis by Gr- not offer a solution. The taxonomy of On edler in 1881, and in the literature there comelania has been subjected to frequent red- were 7 generic names (Oncomelania, Mela- ivision and recombination resulting in confu nia, Hemibia, Prososthenia, Blanfordia, Ka- sion. tayama and Schistosomophora) and 31 new 2. Oncomelanian taxonomy requires in- species (including subspecies). There is no depth investigation : While there was no co doubt that many of them were synonyms; mpatriot specializing in the classification of nevertheless, the possiblility still exists that Oncomelania, a considerable amount of work new species may remain undiscovered. Dur has been done in China on the embryological ing the past 103 years, there have been three development, morphology, anatomy and esp eminent oncomelanian taxonomists, namely, ecially on the ecology and eradication of Annandale (1924), Bartsch (1925, 1936a, Oncomelania; and in the meantime many 1936b, 1939, 1946), and Abbott (1948). An views on the taxonomy of Oncomelania have nandale was a pioneer in the thorough revi been proposed. The opinions of our scholars sion of oncomelanian taxonomy, combining are quite divergent, but one point in common the Chinese (including Taiwan) and the Jap is that they are aware of possible defects anese taxa into one genus (Oncomelania), and errors present in the work on oncomela two groups and five species in all ; and laid a nian taxonomy done abroad. The problem sound foundation for the taxonomy of this of oncomelanian taxonomy is still open, and snail. Bartsch, in dividing the oriental onc- awaits further investigation. Department of Parasitology, Hubei Medical Co 3. Controversy of mono-species versus mu llege, Wuchang, China. lti-species : Despite the much diversified op- ( 53 ) 94 inions both at home and abroad on the tax to the same species. But whether this idea onomy of Oncomelania, by and large they is correct or not remains to be discussed. can be grouped into one of two schools. In recent more than ten years Davis (1967, One school maintains that Oncomelania of 1968, 1969 a, 1969 b, 1971, 1973) has studied the world consists of more than one species, the oncomelaniid snails of Taiwan, Japan, whereas the other school suggests that Onc Philippines and Indonesia. His work is very omelania consists of one genus and one sin careful and his papers are well worth read gle species only. The argument for the for ing, but his idea of Oncomelania taxonomy mer school is that Oncomelania of the world is not necessarily correct. His idea funda has conspicuous morphological distinctions; mentally but not entirely agree with Burch's they are also different with respect to geog (1966, 1967). Davis recognizes only one gen raphic distribution, ecology, physiology, ont us with two species and six subspecies. Th ogeny, immunology and infectivity ; therefore ese taxa are Oncomelania minima from Japan more than one species is present. Most of and the subspecies of Oncomelania hupensis, the oncomelanian research workers in this i.e., O. h. hupensis from mainland China; country and abroad adhere to this view (He- O. h. chiui and O. h. formosana from Tai ude, 1890; Annandale, 1924; Bartsch, 1925, wan ; O. h. nosophora from Japan ; O. h. 1936 a, 1936 b, 1939, 1946; Germain et Ne- quadrasi from the Philippines ; O. h. lindo- veu-Lemaire, 1926; Baylis, 1931 ; Bequaert, ensis from Sulawesi in Indonesia. It is quite 1928, 1934; Abbott, 1948; Yasuraok, 1969, clear that Davis incorporated all the Chinese 1970 ; Sun, 1964), and the writer also shares oncomelaniid snails into a subspecies Onco- their opinion (Kang et al., 1958; Kang, tmelania hupensis hupensis. We considered 1981). Concerning the oncomelanian taxono it is very incorrect. As is known to all, my we will deal with in another article in mainland China is the most important distr detail. We consider that Oncomelania hup- ibuting centre of Oncomelania, where the ensis, O. formosana, O. nosophora, O. qua- vector snail of Schistosoma japonicum is wi- drasi, O. chiui, O. minima, O. tangi, and despred in 12 provinces and 347 counties. O. robertsoni are all distinct species rather Its natural conditions are very complex, and than the same species. species may be numerous. Regrettably, Da The idea of only one genus and one species vis has not studied the Chinese oncomelaniid is held by Kuo and Mao (1957) who proposed snails. Thus his work of Oncomelania tax that the specific term Oncomelania hupensis onomy should not be considered complete. Gredler should be used for all Oncomelania Liu, Y. Y. (1974) first considered that all snails involved in the transmission of sch- the Chinese oncomelaniid snails are probably istosomiasis japonica in China. But later of only one species {Oncomelania hupensis) Mao et al. (1965) also said : "the views with a number of subspecies, but afterwards of our scholars are still divergent on the tax Liu et al. (1981) said all the oncomelaniid onomy of the genus Oncomelania, in line snails distributed throughout the world sho with the materials now available it could uld be regarded as a single species, and not come to a conclusion, and waits for classified it into 10 subspecies. These subs researches." pecies all were originally distinct species. Burch (1960 b, 1964, 1966, 1967) found that They reduced these species to subspecies and the four species (O. hupensis, O. formosana, changed their scientific names from binomial O. quadrasi and O. nosophora) all have the nomenclature into trinomial nomenclature. same number of chromosomes: n = 17, 2n = We considered their justification for doing 34. This cytological finding, coupled with this is not entirely warranted. This change the readiness of hybridization as well as the could only create taxonomic confusion. hybrids' capability of producing fertile offs 4. The criterion of chromosome number pring, led Burch to refer these four species is not yet up to the level of species identi- ( 54 ) 95 fication : Burch's view may seem justified belonging to the same species, then all the at first glance, but may not be correct. In species of the genus Bulinus and the genus order to elucidate the problem, a considera Biomphalaria should be merged into one tion on the usefulness of chromosome number species. Yet Burch did not say that they are for taxonomical work seems necessary. Acc of the same species; on the contrary he ording to the literature available to us, chro admitted that chromosome numbers, as a ge mosome number is of limited significance neral chracteristic, could not facilitate the in taxonomical work. It cannot serve as the taxonomy of these snails. sole criterion for the classification of mollus- Recently I received a letter from Professor can species. Likewise, it cannot serve as the Tan Jia-zhen, the Chinese geneticist, in wh sole criterion of oncomelanian taxonomy. ich he pointed out : "(1) The number of Early in 1960, Burch himself pointed out chromosomes is not a definite indicator of that the monocentric and elongate features species because different species may have of chromosomes are the same with aquatic the same number of chromosomes. For exa pulmonate snails as with terrestrial ones, and mple Triticum dicoccum and Triticum dico- cannot be used to distinguish the two Order ccoides are different species, but their mor (Basommatophora and Stylommatophora). phology and number of chromosomes are Eight species belonging to five families of the same. (2) The individuals of the species Basommatophora have no pronounced differ may have different number and morphology ence in the configuration of chromosomes. of chromosomes such as the individuals of As to the number of chromosomes, the hap- Catantops brachycerus Will, have different loid number are all 18 except one species chromosome morphology. Such instances are (n = 17); thus, he admitted that chromosome too numerous to mention." Therefore, based number by itself has very limited value. on the data available, chromosome number Patterson (1967), on the basis of published in snails cannot serve as the basis of species literature, tabulated the chromosome numb identification. The identical chromosome ers of streptoneuran snails, most of the species number in the four species of Oncomelania having the same number of chromosomes.