completely, and provided with minimal difficulty and cost to any competent researcher who wishes to study them. After 1999, there must be an explicit fixation of a holotype or syntypes and indication of where these specimens are depositied. The type for the genus is a species, which is often established by original designation, by some indication, or by subsequent designation. Since many ciliate genera were monotypic when first established, there is no ambiguity regarding the type-species. At the family level, the type-genus is usually easily recognized as the family name is typically based on it, although there are exceptions (Corliss, 1962a, 1962b, 1977). 3.3.2 Important Dates As noted above, \u201cyear zero\u201d for the Code is 1st January 1758, dating from the year in which Linnaeus (1758) first published his Systema Naturae (Art. 3.2; Code). Prior to 1900, names published as vernacular names and generally accepted by the specialist community are avail- able (e.g., Bursariens of Dujardin as Bursariidae Dujardin, 1841; see Corliss, 1962a). Beginning 1st January 1931, it was necessary to designate a type species to establish a valid genus name (Art. 13, 68; Code). If this was not done, the name technically becomes a nomen nudum or \u201cnaked name.\u201d Prior to 1931, the name may be acceptable provided it was at least accompanied by a description, definition or other indication. After 1999, there must be an explicit fixation of a holotype and indication of where this specimen is deposited, and the taxon must be explicitly indicated as new by using \u201cn. sp.\u201d, \u201cn. gen.\u201d, and \u201cn. fam.\u201d or equivalent designation. Foissner and Berger (1999) provide an excellent treatment of the problems arising from nomina nuda that arose during molecular biological investigations of the oxytrichid stichotrichs . If a name has not been in practical use for at least 50 years \u2013 the \u201c50-year\u201d rule, it can be considered a nomen oblitum or forgotten name. Thus, an unused senior synonym (i.e., older name) cannot replace a junior synonym (i.e., younger name) that has been in general use. 3.3.3 About Names Once fixed by a nomenclatural author, a name- bearing type cannot be changed. Names are con- sidered available when they are published in a work that is in hard copy, publicly available, and produced in sufficient copies. Names published in theses and abstracts are generally considered not to be available. The principle of homonymy states that no two scientific zoological names can be spelled iden- tically. Thus, all other things being equal, the principle of priority will dictate which name shall remain valid and which name must be replaced. It is recommended that differences in one letter should be avoided. Whether names have been used before can be discovered by consulting indexes in the Zoological Record and of S. A. Neave. Aescht (2001), noting that these are not perfect records, emphasized that there is no substitute for a thorough personal knowledge of the relevant literature. If two different names refer to the same name- bearing type, they are called objective synonyms or nomenclatural synonyms . The nomenclatural decision here is therefore unambiguous based on the rule of priority: the junior objective synonym , that is the more recent name, must be taken out of use. Sometimes, however, there is ambiguity in regard to the name-bearing type, especially in the proto- zoological literature in which written descriptions and/or figures may be the only means of understand- ing the features of the name-bearing type. In this case, a later worker may decide from the evidence that two different names, in their opinion, refer to the same species. These names would be considered subjective synonyms because they are based on the subjective judgement of that particular taxonomist. Subjective decisions are never definitive since they are a matter of opinion. Nevertheless, the reviser may invoke the rules of priority and recommend that the junior subjective synonym be taken out of use. There are numerous rules and recommendations with regard to the technical formation of names. Simply, scientific names of organisms should be Latin or latinized, regardless of their etymologi- cal origin. The genus name begins with a capital letter and is a substantive or noun or adjective of a substantive or noun. When publishing the name, it is advisable to state its derivation or etymology. In addition, the gender of the genus name should be indicated. The gender can be determined by referring to standard Greek and Latin dictionaries. If the genus name is a compound word, it should take its gender from the last component (Art. 30; Code). Refer to Corliss (1962a, 1962b), Aescht (2001), and the Code for more detailed information and advice. 3.3.4 Summary The above discussion is meant to provide a brief introduction to the rules of nomenclature. Nothing substitutes for a reading of the most recent edition 3.3 Taxonomy and Nomenclature 87 88 3. Characters and the Rationale Behind the New Classification of the Code. While the Code was established to promote stability, circumstances arise from time-to- time when the preservation of names that contra- vene the Code is seen to be in the best interests of the scientific community: stability is preserved in these cases even though the rules of the Code would be violated. In this event, a petition may be submit- ted to the International Commission on Zoological Nomenclature , arguing the case for the conservation of a name. For example, an appeal for conservation of the genus Tetrahymena Furgason, 1940 was made by Corliss and Dougherty (1967) while a more recent case, for example, was made by Corliss and Foissner (1997) for conservation of authorship for Trachelocerca Ehrenberg, 1840. Supportive rulings in relation to these petitions were respectively made by the International Commission on Zoological Nomenclature (1970, 1999b).